Weaning The Pig: Concepts and Consequences

Weaning the pig Concepts and consequences Edited by: J.R. Pluske J. Le Dividich M.W.A. Verstegen Weaning the pig – co...

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Weaning the pig Concepts and consequences

Edited by: J.R. Pluske J. Le Dividich M.W.A. Verstegen

Weaning the pig – concepts and consequences

Weaning the pig concepts and consequences

Edited by: J.R. Pluske J. Le Dividich M.W.A. Verstegen

Wageningen Academic P u b l i s h e r s

ISBN: 978-90-76998-17-6 e-ISBN: 978-90-8686-513-0 DOI: 10.3920/978-90-8686-513-0

Subject headings: Growth Digestive physiology Fertility

First published, 2003

Photo cover: J. Chevalier (INRA)

© Wageningen Academic Publishers The Netherlands, 2003

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned. Nothing from this publication may be translated, reproduced, stored in a computerised system or published in any form or in any manner, including electronic, mechanical, reprographic or photographic, without prior written permission from the publisher, Wageningen Academic Publishers, P.O. Box 220, 6700 AE Wageningen, the Netherlands, www.WageningenAcademic.com The individual contributions in this publication and any liabilities arising from them remain the responsibility of the authors. The publisher is not responsible for possible damages, which could be a result of content derived from this publication.

Contents 1

Introduction J.R. Pluske, J. Le Dividich and M.W.A. Verstegen

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2

Growth of the weaned pig I.H. Williams 2.1 Introduction 2.2 The potential growth of weaned pigs 2.3 Description of growth 2.4 The growth check at weaning 2.5 Bodyweight at weaning - its importance for post-weaning growth 2.6 Can weaning weight be increased by supplementary feeding? 2.7 Do pigs stimulated to reach higher weaning weights grow faster to slaughter? 2.8 Do pigs exhibit compensatory growth? 2.9 The importance of weight gain in the first week after weaning 2.10 Minimising the growth check at weaning 2.11 Does minimising the growth check have long-term benefits? 2.12 Conclusions References

17

3

4

Nutritional management of the pig in preparation for weaning R.H. King and J.R. Pluske 3.1 Introduction 3.2 The importance of weaning weight to subsequent growth 3.3 Nutrient intake before weaning 3.3.1 Supplying creep food in lactation 3.3.2 Dry creep feed intake 3.3.3 Liquid diets to enhance feed intake 3.3.4 The effects of gender on nutrient intake of neonatal pigs 3.4 The composition of diets offered during lactation 3.4.1 Dietary formulation of creep diets 3.4.2 Use of flavours in creep/starter diets 3.4.3 Presentation of the creep diet 3.5 Water for suckling pigs 3.6 Conclusions References Behavioural changes and adaptations associated with weaning P. Mormède and M. Hay Summary 4.1 Introduction

Concepts and consequences

17 17 18 19 20 21 23 25 26 27 29 31 31 37 37 38 39 39 40 41 43 43 44 45 45 47 47 48 53 53 53

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6

7

8

4.2 Neuroendocrine consequences of weaning 4.3 The critical role of food 4.4 Behaviour 4.5 Conclusion References

54 54 57 57 58

Metabolic and endocrine changes around weaning F.R. Dunshea 5.1 Introduction 5.2 The post-weaning check 5.3 Effect of weaning on metabolism 5.3.1 Lipid and carbohydrate metabolism 5.3.2 Protein metabolism 5.4 Hormonal status 5.4.1 Somatotropin and insulin-like growth factor-I 5.4.2 Insulin 5.4.3 Hypothalamic-pituitary axis 5.5 Conclusions References

61 61 61 65 65 67 68 68 72 72 74 74

Factors affecting the voluntary feed intake of the weaned pig P.H. Brooks and C.A. Tsourgiannis 6.1 Introduction 6.2 Feeding behaviour of piglets kept under ‘natural’ or ‘semi-natural’ conditions 6.3 Commercial weaning practice - an event rather than a process 6.4 Pre-weaning feed and water intake 6.5 Relationship between pre-weaning food consumption and post-weaning growth 6.6 Feeding behaviour of the post-weaned pig 6.7 Feed and water intake of weaned pigs 6.8 The significance of maintaining continuity of food intake after weaning 6.9 The interaction between water and feed intake post weaning 6.10 Liquid feeding post-weaning 6.11 Conclusions References Digestive physiology of the weaned pig H.M. Miller and R.D. Slade Summary 7.1 Introduction 7.2 Strategies for adaptation to enteral nutrition in the neonatal pig

81 81 81 86 87 91 94 96 99 102 106 108 109 117 117 117 118

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Contents

7.2.1 Preparation 7.2.2 Implementation I 7.2.3 Perspective 1 7.3 The weaned pig 7.3.1 Commercial weaning 7.3.2 Gastrointestinal, pancreatic and hepatic response 7.3.3 Small intestine morphological response 7.3.4 Small intestine carbohydrase and transporter response 7.3.5 Amino acid transport 7.3.6 Perspective 2 7.4 Regulation of post-weaning adaptation 7.4.1 Milk withdrawal 7.4.2 Weaning stress 7.4.3 Direct dietary effects 7.4.4 Indirect dietary effects 7.4.5 Perspective 3 References 8

9

Diet-mediated modulation of small intestinal integrity in weaned piglets M.A.M. Vente-Spreeuwenberg and A.C. Beynen Summary 8.1 Introduction 8.2 Small intestinal integrity 8.2.1 Small intestinal morphology 8.2.2 Mucus production 8.2.3 Transepithelial permeability 8.2.4 Inflammation 8.2.5 Brush border enzyme activity 8.2.6 Animal performance 8.3 Modulation of small intestinal integrity by luminal nutrition 8.3.1 Modulation by route of administration 8.3.2 Modulation by level of energy intake 8.3.3 Modulation by dietary components 8.4 Concluding remarks References Interactions between the intestinal microflora, diet and diarrhoea, and their influences on piglet health in the immediate post-weaning period D.E. Hopwood and D.J. Hampson Summary 9.1 Changes in intestinal microflora at weaning


118 120 122 122 123 123 124 127 128 129 130 130 131 132 134 138 139

145 145 145 147 148 149 149 150 150 151 151 152 155 159 185 186

199 199 199

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Contents

9.2 Major enteric diseases at weaning 9.3 Post-weaning colibacillosis (PWC) 9.4 Factors predisposing to post-weaning colibacillosis at weaning 9.4.1 The role of the small intestine 9.4.2 The role of the large intestine 9.4.3 The specific role of diet 9.4.4 The specific role of dietary non-starch polysaccharides in PWC 9.5 Conclusions Acknowledgements References 10 Aspects of intestinal immunity in the pig around weaning M.R. King, D. Kelly, P.C.H. Morel and J.R. Pluske 10.1 Introduction 10.2 Overview of immune systems 10.2.1 Active immunity 10.2.2 Passive immunity 10.3 The intestinal immune system 10.3.1 Intestinal inflammation 10.3.2 Oral tolerance 10.3.3 Development of intestinal immunity 10.4 The effect of weaning on the intestinal immune system 10.4.1 Overview of the weaning process 10.4.2 Alteration of intestinal morphology 10.4.3 Activation of the intestinal immune system 10.5 Conclusion References 11 Nutritional requirements of the weaned pig M.D. Tokach, S.S. Dritz, R.D. Goodband and J.L. Nelssen Summary 11.1 Introduction 11.2 Importance of pig weight and age 11.3 Basis of nutrient specifications for weaner pigs 11.3.1 Ingredient selection based on digestive capacity 11.4 Nutrient requirements of the weaned pig 11.4.1 Energy 11.4.2 Amino acids 11.4.3 Other approaches to determining a requirement estimate 11.4.4 Vitamins 11.4.5 Minerals 11.4.6 Post-weaning diarrhea and zinc oxide. 11.4.7 Organic trace minerals

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201 202 204 204 205 205 206 211 212 212 219 219 220 220 223 224 227 228 231 233 233 234 236 244 244 259 259 259 259 262 263 264 264 264 265 268 269 270 271

Weaning the pig

Contents

11.5 11.5.1 11.5.2 11.5.3

Selection of ingredients for the weaned pig Energy sources Protein sources Non-nutritive Feed additives (eg., antibiotics, enzymes, organic acids, etc.) 11.6 Example of phase feeding program for early weaned pigs 11.6.1 SEW diet - weaning to 5 kg 11.6.2 Transition diet - 5 to 7 kg 11.6.3 Phase 2 - 7 to 11 kg 11.6.4 Phase 3 - 11.5 to 23 kg 11.7 Importance of management in the success of the nutritional program 11.7.1 Management to encourage feed intake 11.7.2 Adjust feeders frequently to minimize feed wastage References 12 Intestinal nutrient requirements in weanling pigs D. Burrin and B. Stoll 12.1 Introduction 12.2 Changes in gut physiology during weaning 12.2.1 Acute phase 12.2.2 Adaptive phase 12.3 Intestinal nutrient utilization in young pigs 12.3.1 Physiological and cellular basis of gut metabolism 12.3.2 Major oxidative fuels 12.3.3 Essential amino acid utilization 12.3.4 Interactions between nutrition and enteric health and function 12.4 Summary and perspectives Acknowledgments References 13 Environmental requirements and housing of the weaned pig F. Madec, J. Le Dividich, J.R. Pluske and M.W.A. Verstegen 13.1 Introduction 13.2 Environmental requirements of the weaned pig 13.2.1 Events related to weaning that affect thermal requirements 13.2.2 Ambient temperature 13.2.3 Relative humidity and ventilation 13.2.4 Lighting 13.2.5 Effects of non-optimal climate on performance 13.3 Pen structure 13.3.1 Flooring materials 13.3.2 Feeders and waterers


272 272 275 282 283 283 285 286 287 288 289 289 290 301 301 301 302 304 306 307 311 314 320 324 324 325 337 337 338 338 339 343 344 344 346 346 346

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13.3.3 13.3.4 13.4 13.4.1

Stocking densities Group size Housing as a cause of poor health of weaned pigs Evidence that housing conditions predispose pigs to digestive disorders 13.4.2 Impact of non-optimal indoor climate on the pig’s health status 13.4.3 Multifactorial nature of post-weaning disorders: risk factors associated with housing and management 13.4.4 Integrating the risk factors to improve health 13.5 Conclusion References 14 Saving and rearing underprivileged and supernumerary piglets, and improving their health at weaning J. Le Dividich, G.P. Martineau, F. Madec and P. Orgeur 14.1 Introduction 14.2 What are underprivileged and supernumeraries? 14.3 Reasons accounting for variation in birthweight and weaning weight 14.3.1 Variation in birth weight 14.3.2 Variation in weaning weight 14.4 Differences between underprivileged and “normal” piglets 14.4.1 Body composition 14.4.2 Performance of underprivileged pigs 14.5 Management practices to improve survival and growth of the underprivileged pigs 14.5.1 Providing assistance to the underprivileged piglets at birth 14.5.2 Cross fostering 14.5.3 Split weaning 14.5.4 Feeding strategy 14.6 Growth potential of underprivileged piglets 14.7 Supernumerary piglets 14.7.1 Weaning at day 1-3 14.7.2 Fostering onto a nurse sow 14.7.3 Weaning at one week of age 14.8 Management to improve the health of piglets 14.8.1 All-in / All-out management system 14.8.2 Segregation 14.9 Conclusion: the need for research References

12

347 348 349 349 350 351 353 353 355

361 361 362 363 363 364 365 365 366 367 368 369 370 370 371 371 372 372 372 373 373 374 376 377

Weaning the pig

Contents

15 Productivity and longevity of weaned sows A. Prunier, N. Soede, H. Quesnel and B. Kemp 15.1 Introduction 15.2 Reproductive causes of culling 15.3 Consequences of lactation and weaning on the reproductive axis 15.3.1 Postpartum inhibition 15.3.2 Removal of the inhibition of the hypothalamic-pituitaryovarian axis at weaning 15.4 Variation in reproductive performance: extent and sources of variation 15.4.1 Components of fertility and prolificacy 15.4.2 Influence of nutritional factors 15.4.3 Influence of lactational characteristics 15.4.4 Influence of the physical and social environment 15.4.5 Relationships between WEI, litter size and farrowing rate 15.5 Conclusion References

385 385 385 388 388 392 394 394 394 402 404 406 408 409

Conclusions

421

List of authors

422

Index

425


13

1

Introduction

The weaning age of pigs has been reduced from about 8 weeks of age in the 1950s and 1960s down to a current average weaning age of 22-26 days of age that is practiced in many pig-producing countries, although even earlier weaning ages (< 21 days) are adopted with some systems. The reduction in weaning age occurred largely because of the productivity increases, both in the growing and breeding herds, which were achievable. However, the inevitable shift to earlier weaning ages presented many problems concerning the nutrition, housing, health, behavioural and environmental requirements of the young pig, as well as having consequences for the fertility of the sow. These are especially pertinent in systems where pigs are weaned at less than 21 days of age, such as segregated early weaning practices. Much research, combined with field experience, has minimized the stressors encountered at weaning so that good levels of production can be achieved after weaning. Nevertheless, changes in the global business of pig production continue to occur and must be dealt with. Of recent interest, particularly in Europe, has been the increasing awareness in society with respect to animal welfare, food safety, the environment, and the ‘quality’ of production, especially with respect to antibiotics as growth promoters. These (relatively) recent events have instigated a flood of new research into fields concerning, for example, optimum gut ‘health’ and immune function that, until recently, have largely been ignored in weaner pig production. Consequently, issues such as enteric diseases, welfare and the intestinal nutritional requirements of the weaned pig are under increased scrutiny and attention as producers, feed manufacturers, scientists and managers attempt to resolve these new issues. It is also increasingly evident that the events surrounding weaning can have profound and life-long consequences in both the growing and breeding herds. Collectively, the process of ‘weaning’ has never been considered as more important as it is nowadays. In light of these changes and developments, “Weaning the Pig: Concepts and Consequences” is timely and has been compiled to provide the reader with an up to date account of all facets related to the weaning process, including the fate of the weaned sow. The material in the book covers the following areas associated with the weaning process: growth of the weaned pig, nutritional management in preparation for weaning, behavioural changes and adaptations around weaning, voluntary feed intake, digestive physiology, modulation of small intestinal integrity, the intestinal microflora and diarrhoeal diseases after weaning, intestinal immunity, nutritional requirements and intestinal requirements of the weaned pig, environmental and housing issues after weaning, saving and rearing supernumery and underprivileged piglets, and productivity and longevity of the weaned sow.


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Pluske, Le Dividich and Verstegen

World-renowned experts and specialists from numerous countries have written the chapters, and are applicable to all people involved in pig production, health and disease, research, management and extension throughout the world. The information contained can be used to modify and (or) develop nutritional, environmental, housing, disease, welfare and management strategies to best handle the weaning process. Developments in our knowledge may also help to update courses in the field of pig science and to interest those who teach animal production principles. John Pluske Jean Le Dividich Martin Verstegen

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2

Growth of the weaned pig I.H. Williams

2.1

Introduction

Pigs are capable of extremely rapid growth after weaning but there are a host of factors that limit the extent to which this potential is expressed. The weight of the pig at weaning, its nutrition and growth rate in the immediate post-weaning period, and the physical, microbiological and psychological environment are all factors that interact to determine food intake and subsequent growth. The age at weaning is variable and so weight at weaning can vary two or three fold. In most countries it is common practice to wean at 3 to 4 weeks when pigs weigh in excess of 6 kg but, in other countries, particularly North America, weaning pigs before three weeks of age of age is common. The main reason for early weaning is to reduce the transfer of disease from the sow but younger, lighter piglets require a higher standard of management and require better nutrition and more stringent environmental conditions. This chapter begins by outlining the young pig’s potential for growth followed by a simple description of growth and its principles. This is followed by a consideration of how bodyweight and nutrition impinge on growth. Other factors that limit growth will be considered in subsequent chapters.

2.2

The potential growth of weaned pigs

Growth rates of 100, 200 and 400 g/d in the first, second and third weeks after weaning at 21 days have been suggested by Whittemore and Green (2001) as commercially acceptable targets in the absence of observed clinical disease and overt stress. However, these growth rates represent substantial underperformance. The same authors suggest that a healthy pig at 3 weeks of age weighing 5 kg and given unrestricted food intake in the experimental facility at Edinburgh will grow at 500 g/d, twice the commercial performance. Yet even this rapid growth may not represent the true growth potential of the young pig. If piglets are weaned very early in life (1 to 2 days) and given liquid diets based on cow’s milk, growth rates in excess of 500 g/d can be achieved. For example, Hodge (1974) removed piglets from the sow when they were 2 days old and fed them ad libitum on reconstituted cow’s whole milk. Between 10 and 30 days of age his pigs grew at 571 g/d and between 30 and 50 days of age they grew at 832 g/d. Similar growth rates for piglets removed from sow at 2 days of age and fed milk have been demonstrated by Williams (1976) and by Harrell et al. (1993). If similar


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experiments to those of Hodge (1974) were conducted with modern-day genotypes, piglets might grow even faster on milk and demonstrate a higher potential. There can be no doubt that the potential for growth of the young pig is extremely high and is between two and three times that which is commonly observed under the best commercial conditions. The question is, why is this potential rarely if ever reached and what can be done to lift performance closer to potential?

2.3

Description of growth

There has been much debate in recent years about the best way to describe growth because of the interest in modelling growth (Black, 1995). Most models are based on a prediction of the protein mass and its incrementation, and some defined relationship between the gain in protein and lipid. Gains in protein and lipid are summed to give gain in liveweight. If the liveweights of animals that have been fed ad libitum on high-quality diets throughout life are plotted against time they produce an “S-shaped” curve, termed a sigmoidal growth curve (Lawrence and Fowler, 1997). Whittemore and Green (2001) have put forward a compelling argument that the sigmoid growth in pigs from birth to maturity can best be described by a Gompertz function: Daily gain = liveweight * B * ln(weight at maturity/liveweight), where B is a growth coefficient. Sigmoidal growth has two main phases. The first is early in life where growth increases. The second is where growth decreases and finally ceases when animals reach maturity. These phases are linked at the point of inflection where growth is linear and this generally occurs at approximately one third of mature body size (Lawrence and Fowler, 1997). The weaned pig fits into phase one, that of increasing or accelerating growth. The Gompertz function requires two parameters, an asymptote or description of maturity and a growth coefficient, which are not independent of each other. An increase in one will be accompanied by an increase in the other. This has some important ramifications for the growth of animals. It means that animals have predetermined growth paths and that there are large, fast growing animals and smaller, slower growing animals. It means that a larger genotype or a pig with a greater propensity for growth will, at any age, be bigger and grow faster than a smaller genotype.

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Weaning the pig

Growth of the weaned pig

What the Gompertz function does not describe is the growth check that usually occurs at weaning and the recovery phase that follows. At weaning it is common for piglets to lose weight and display negative growth for several days and not recover their pre-weaning weight for perhaps 7 or even 10 days (Pluske et al., 1995). When they do begin their recovery phase, do they exhibit any signs of compensation? That is, do they grow faster than their contemporaries at the same weight who have not experienced the same check in growth or do they grow at the same rate and simply take longer to market weight. This will be addressed later in this chapter.

2.4

The growth check at weaning

At weaning the piglet faces three challenges. First, there are major changes to its food supply. Not only does the piglet have to find its own food from a creep feeder but the new food is more bulky, is often composed of ingredients that the piglet has not previously encountered, and it is 88% dry. By contrast, sow’s milk is 80% water and the dry matter (20%) is composed of protein (30%), fat (40%) and lactose (25%), but no starch. True digestibilities of fat and lactose are close to 100% and ileal digestibilities of amino acids are also very high at 92% (Mavromichalis et al., 2001). Creep feed is less digestible (80 to 90%), often contains a mixture of plant and animal proteins, contains mostly starch instead of lactose, and has very little fat relative to sow’s milk. As a consequence the digestive tract of the piglet has to make a major shift away from digesting fat towards digesting complex carbohydrates. In addition, it has to cope with a very large increase in dry matter intake if the growth of the newly-weaned piglet is to be maintained. For example, a piglet growing at 250 g/d would need to eat about 200 g of dry matter per day from sow’s milk while consumption of a high-density creep would need to reach at least 300 g/d, a 50% increase, and even more if lower-quality creep diets are used. Associated with these changes in the supply of food are alterations of the digestive tract that may have long-term (one or more weeks) ramifications. When the milk supply ceases abruptly the structure and function of the digestive tract begins to change immediately within hours. Villous height reduces, crypt depth increases, and there is a reduction in the absorptive capacity because the specific activity of the digestive enzymes, lactase and sucrase, decreases. Poor absorption of nutrients in the small intestine is often associated with proliferation of enterotoxigenic bacteria (mainly Escherichia coli) and/or fermentation of less digestible nutrients in the large intestine (McCracken and Kelly, 1993). Either way, this may lead to diarrhoea. The second major challenge at weaning for the piglet is to cope with the change in the physical environment. At weaning litters are generally mixed together into weaner pools. Having learnt to live in the farrowing pen with its mother and littermates it now has to learn to live without its mother and face competition with many more pigs, up to 250. The problem is to design a weaner pen that allows


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individual piglets to find their own comfort zone. Because of the great variation in food intake it is almost impossible to design an environment where all piglets will be within their thermoneutral zone. For example, when a piglet increases its food intake from maintenance to twice maintenance its lower critical temperature is reduced by 3°C (Close and Stanier, 1984). So there could be a difference of 12°C in lower critical temperature between a piglet that is not eating compared with one that is eating at maximum, say 4 times maintenance. If room temperatures are set to keep the pigs that are eating within their thermoneutral zone then the piglets not eating will be severely cold stressed. If room temperatures are raised so that piglets not eating are within their comfort zone, other piglets that are eating are likely to be heat stressed. The third challenge at weaning is the psychological stress that accompanies moving and mixing. Although many workers believe that this depresses growth the extent of this influence is unknown, but will be considered in a subsequent chapter. When all these changes are taken into account it is little wonder that the rate of growth of the piglet falls after weaning, and the extent of the depression in growth depends on how rapidly the piglet can adjust to its new circumstances and regain homeostasis.

2.5

Bodyweight at weaning - its importance for post-weaning growth

The Gompertz description of growth predicts that a pig of large mature body size will be larger and grow faster at any given age than a pig of smaller size. Producers have always known that heavier pigs at birth are heavier at weaning and that heavier pigs at weaning grow faster after weaning than smaller pigs and, in most instances, are also heavier at slaughter. So the difference in weight at weaning is not just maintained but it is magnified as the pig grows because the heavier pigs grow faster than their lighter counterparts at all ages. There are several studies that substantiate this view. Birth weight is positively correlated with weight at weaning (McBride et al., 1965; McConnell et al., 1987; Cranwell et al., 1995; Dunshea et al., 2003), weight at one week of age is highly correlated with weaning weight (Miller et al., 1999) and weight at weaning is highly correlated with post-weaning performance (Miller et al., 1999; Lawler et al., 2002). There are also several studies where bodyweights at various ages have been quantified for their influence on subsequent growth to slaughter. Campbell (1989) analysed the weaning records from a large piggery in Australia and found that a difference of 1.8 kg between pigs weaned at 25 to 29 days of age (6.14 verses 7.95 kg) increased to 5 kg at 78 days and 10 kg at 150 days. Mahan and Lepine

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(1991) found that pigs with weaning weights of 4.1 to 5.0 kg required 11 to 20 days longer to reach slaughter at 105 kg than piglets with weaning weights of 7.3 to 8.6 kg. More recently, Wolter and Ellis (2001) reached a similar conclusion after they found that a difference of 1.5 kg (3.9 versus 5.4 kg) in pigs weaned at 3 weeks of age was translated into a growth difference of 8.6 days at slaughter. In a most comprehensive study on lifetime and post-weaning determinants of performance indices of pigs Dunshea et al. (2003) found that a difference in birthweight of 0.37 kg (1.86 vs 1.39 kg) had increased to 1.9 kg (5.22 vs 3.21 kg) by two weeks of age and 13 kg (107.1 vs 94.3 kg) by 23 weeks of age. Because of the great importance of bodyweight at weaning, research has focused on two questions. Can the growth of piglets during lactation be stimulated so that they are heavier at weaning and, if so, will this larger pig at weaning outperform a lighter counterpart in growth after weaning?

2.6

Can weaning weight be increased by supplementary feeding?

The main argument for offering sucking piglets supplementary food from a creep feeder is that it can satisfy the ever-widening energy gap between the piglet’s energy requirements and the dwindling supply of milk. Since Harrell et al. (1993) have calculated that the supply of sows’s milk probably begins to limit growth at about 10 days of age, piglets offered creep should be heavier at weaning and be better able to withstand the stresses at weaning. In the 1950s and 1960s when it was common to wean piglets at 8 weeks of age, Lucas and Lodge (1961) demonstrated the importance of offering creep feed before weaning. They raised weaning weight from 12 to 20 kg but found that significant consumption of creep did not begin until the piglets were four weeks or older. As the age of weaning was reduced to as little as two or three weeks it was thought that creep feeding might become even more important because of the susceptibility of smaller pigs to adverse environmental conditions. However, despite a large number of studies conducted in many parts of the world the magic formula that encourages creep consumption before the piglets were 3 weeks of age has eluded research workers and producers. Pluske et al. (1995) analysed the results of several experiments and reached two conclusions. First, that consumption of creep feed before weaning is highly variable and at best might contribute approximately 17% of energy intake and, at worst, zero. Perhaps more baffling is the relatively poor relationship between the amount of creep consumed and the weight at weaning suggesting that creep feed might be a substitute for rather than a supplement to sow’s milk. This is exemplified by the work of Toplis et al. (1999) who introduced creep at 14 days and then weaned the piglets at 24 days. Piglets receiving no creep weighed 6.9 kg at weaning, those that were offered creep


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in dry form consumed 91 g over the 10 days and were 6.5 kg at weaning, and piglets offered creep as a gruel (1:2 meal to water) ate 374 g/piglet over the 10 days and weighed 6.7 kg. So despite consuming sufficient gruel that should have, by calculation, increased weaning weight by about 5%, no increase could be measured. A similar example comes from the work of Brown et al. (1999). They coaxed sucking piglets to drink cow’s whole milk at 12 days of age and measured a mean dry matter intake of 332 g dry matter/week between 12 and 19 days, an intake that should have been sufficient to stimulate growth by about 0.4 kg. Yet they found that the piglets that drank milk were the same bodyweight as the controls at weaning at 19 days. Growth of piglets during lactation can be stimulated if food is offered in a liquid form early enough in life, and Reale (1987) was one of the first to demonstrate this. He offered milk to piglets when they were a week old and, by the time they had reached a weaning age of four weeks, they weighed 9.6 kg and had grown an extra 1.8 kg (24% increase in weight) over piglets not receiving supplementary milk. Similar results have been obtained by Dunshea et al. (1997b), who offered supplemental milk to piglets at 10 days of age and measured a 10% stimulation in growth by the time the pigs were 20 days old. As suggested above, the success of stimulating growth by offering supplementary milk during lactation probably depends on the age that piglets are offered the milk. For example, Armstrong and Clawson (1980) offered milk to piglets at three weeks of age but failed to stimulate growth suggesting perhaps that piglets were too settled in suckling behaviour to take in extra milk. Another way to increase weight at weaning is to split wean the litter, a practice where half the litter is weaned at say 20 days (generally the heavier pigs) leaving the lighter pigs to remain suckling for an extra week to obtain more milk per piglet. Several workers have shown that the light piglets that remain with the sow grow faster than their counterparts that have to compete with their larger littermates (Cox et al., 1983; Edwards et al., 1985; English et al., 1987; Pluske and Williams, 1996). For example, Pluske and Williams (1996) split weaned litters at 22 days of age and demonstrated that the growth rate of light pigs could be increased by 60% in the following week. When the light piglets in the split-weaned litters were weaned at 29 days they weighed 15% more than their counterparts in the full litters. This stimulation of growth was brought about by a 50% increase in milk consumption because the piglets learned to suck multiple teats and there was a longer duration of sucking during letdown. More milk per piglet and better growth of piglets might also be achieved by increasing the milk output of the sow through better nutrition (see a later chapter by R.H. King and J.R. Pluske) or by infusing sows with insulin (see McCauley et al., 1999).

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The conclusion is that supplementary feeding during lactation can increase weaning weight if the food is offered early in life in a liquid form. If the supply of sow’s milk can be increased then weaning weights are likely to be greater. However dry diets are unlikely to be effective if offered early in life and are only likely to be of value in situations where piglets are weaned late, for example, at four or five weeks of age. Supplementary or creep feeding has been practised for reasons other than simply increasing the weight at weaning. It has been suggested that exposure to dry food would allow piglets to learn how to source dry food from a feeder, drink water, accustom the digestive tract to dry food, induce the necessary enzymes for its digestion and help prepare the piglet to cope better with many of the potential allergens contained in plant foods. Evidence that any of these benefits might accrue if creep feed is offered is also scarce. Pluske et al. (1995) concluded that there was a modest but non-significant relationship between gain after weaning and creep intake during suckling. They questioned the value of creep feeding particularly for early-weaned pigs but suggested that creep feed may still be of some value for pigs weaned after 3 weeks of age. However, if piglets can be stimulated to eat a reasonable quantity of creep feed in lactation it may pay dividends after weaning. By feeding gruel, Toplis et al. (1999) stimulated piglets to eat 374g of creep over 10 days and, although this did not increase weaning weight, it did stimulate performance after weaning. Piglets fed gruel grew 150% faster (49 vs 125 g/d) than piglets that ate no creep in the first week after weaning and 30% faster (317 vs 416 g/d) for 5 weeks after weaning.

2.7

Do pigs stimulated to reach higher weaning weights grow faster to slaughter?

The philosophy for stimulating piglets to reach a higher weaning weight is that they will behave in a similar way to piglets that are naturally heavier at weaning and grow faster than piglets not stimulated during lactation. Put another way, can supplementary nutrition during lactation be used to raise a piglet from a lower to a higher growth curve? If food intake is genetically determined to drive growth that is also genetically programmed, as it must be, it is most unlikely that a transient period of higher-than-normal nutrition will alter a long-term food setting in the hypothalamus. If this is correct the expectation would be that any increase in weight brought about an increase in growth would, at best, be maintained and, at worst, disappear with time. There have been many attempts to increase weaning weight but relatively few attempts to measure the long-term benefits. Offering piglets dry food from a creep has mostly been unsuccessful in stimulating growth during lactation but increasing


23

Williams

the milk available to each piglet by split weaning or offering it as a supplement has consistently stimulated growth. Pluske and Williams (1996) increased the growth of light piglets by split weaning litters at 3 weeks of age. These piglets grew faster than their contemporaries left as whole litters and weighed 1 kg more at full weaning at 4 weeks (7.7 vs 6.7 kg). However by nine weeks of age the difference in weight had vanished (19.3 vs 19.3 kg). Edwards et al. (1985) achieved a weight difference of 0.4 kg by split weaning and noted that post-weaning growth rate was no different between the heavy and light pigs. Wolter et al. (2002) stimulated the growth of piglets by offering supplementary milk at 3 days of age. By 3 weeks the supplemented piglets weighed 0.9 kg more (6.6 vs 5.7 kg) than the unsupplemented piglets. This increase in weight was not translated into a significant increase in post-weaning growth and overall growth from weaning to 110 kg was almost identical for the supplemented versus the unsupplemented pigs (827 vs 820 g/d). By contrast Dunshea et al. (1997a) found that increasing growth rate during suckling had longer-term benefits. They found that skim milk fed to piglets at 10 days of age increased weaning weight by 0.7 kg of (7.3 vs 6.6 kg) and that this extra growth was still evident at 42 days (14.7 vs 12.2 kg) and 120 days (64.5 vs 60.6 kg). Do the data of Dunshea et al. (1997a) suggest that supplementary feeding has stimulated piglets to a higher growth path? The answer is uncertain but recent data from Wolter et al. (2002) are helpful in addressing this question. In an elegant experiment and, to my knowledge the only one of its kind, Wolter et al. (2002) investigated how weaning weight affected growth to slaughter. They attempted to measure the importance of weaning weight as a measure of the growth curve versus weaning weight as consequence of previous nutrition. They separated piglets into light and heavy at birth and supplemented half the piglets with a milk replacer beginning at three days of age (Table 2.1). By separating pigs at birth into light

Table 2.1. How birth weight (Heavy vs Light), weaning weight and supplementary milk in lactation (Milk vs No milk) influence food intake and growth to slaughter (from Wolter et al., 2002).

Weight (kg) Birth Weaning (20d) Weaning to 110 kg liveweight Food intake (g/d) Growth rate (g/d)

24

Heavy

Light

Milk

No milk

1.83 6.6

1.38 5.7

1.58 6.6

1.58 5.7

1866 851

1783 796

1841 827

1808 820

Weaning the pig


and heavy they achieved a weight difference at weaning of 0.9 kg. The same difference in weight was induced at 20 days by feeding half the piglets supplementary milk. The pigs that were heavier at weaning because of their birth-weight advantage ate more food and grew faster (7%) after weaning than their lighter counterparts. By contrast, the pigs that were heavier at weaning because they were offered supplementary milk during lactation failed to maintain the advantage and consumed similar amounts of food as their lighter counterparts. Wolter et al. (2002) concluded that supplemental milk replacer is unlikely to be an effective strategy for increasing post-weaning performance. However, the work of Dunshea et al. (1997a) cannot be ignored and a possible explanation of their results is that they provided a supplement that allowed pigs to exhibit compensation, a topic discussed in the next section.

2.8

Do pigs exhibit compensatory growth?

Compensatory or catch-up growth is the growth of an animal fed ad libitum after a period of nutritional stress, and it is higher than the growth of a genetically-identical animal in the same environment at the same body weight during normal growth (Hogg, 1991). Interest in compensatory growth began initially with grazing animals because in most temperate parts of the world there is an abundance of food at one time of the year and a scarcity at another. This leads to rapid growth at one time of the year followed by weight loss at another. Whether animals exhibit compensatory gain after a period of restriction depends on several factors including the severity of restriction, the duration of the restriction and the stage of maturity when the restriction is applied; the younger the animal, the less likely it is to exhibit compensatory growth. For example, sheep less than 3 months old (Ryan, 1990) and cattle below 4 months old (Morgan, 1972) do not show compensatory growth. Pigs might be different. McCance (1960) weaned piglets at 10 days of age and severely restricted their food intake so that they gained only 2 kg in a year. When allowed to rehabilitate with food offered ad libitum they grew at high rates and, according to Widdowson and Lister (1991), showed some signs of compensatory growth despite the young age at which their gross nutritional insult was imposed. Despite an exhaustive literature on compensatory growth (see reviews by O’Donovan, 1984; Ryan, 1990; Hogg, 1991; Lawrence and Fowler, 1997) the underlying mechanisms remain elusive. The most consistent observations in compensating animals are that they are more efficient in the initial stages of rehabilitation and that this may be followed by a higher-than-normal food intake. The common explanation for increased efficiency involves changes in size and possibly metabolic activity of the internal organs such as the liver, kidney, and gastro-


25

Williams

intestinal tract. In a well-nourished animal these organs make up 10 to 15% of the liveweight and make a disproportionately high contribution to the fasting heat of production, about 40% (Koong et al., 1983). When nutrition is restricted these organs reduce in size and possibly metabolic rate and this allows the animal to conserve energy and function on less. When rehabilitation begins and food becomes available, these organs take time to build up their size and metabolic rate and, in the meantime, there is extra energy available for the animal to deposit in body tissues. Pigs reared under intensive conditions are in a very different situation from grazing animals and are rarely short of food or specific nutrients except in the early stages of their growth, that is, before weaning and just after. At weaning the stresses are often sufficient to reduce food intake to very low levels and growth is often zero or negative, a situation where compensatory growth might apply. Sow’s milk has low protein relative to its energy content and is deficient in protein for maximum lean gain (Campbell and Dunkin, 1982; Williams, 1995). After about 10 days of lactation the potential intake of milk by the piglets begins to exceed the production from the sow so growth of the piglets starts to fall below their potential (Harrell et al., 1993). So the relative deficiency of protein plus the restriction in quantity of milk that together limit growth represent another situation that might invoke compensation. Several workers have demonstrated compensatory growth in young pigs but the most comprehensive experiments are those of Campbell and Dunkin (1983a, b and c) who have clearly demonstrated that very young pigs will compensate when deprived of protein or energy or both, and will do so even when given fixed intakes of food. In the previous section reference was made to work of Dunshea et al. (1997a) who supplemented piglets at 10 days of age with skim milk and measured a 0.7 kg increase in weaning weight which was still evident at 60 kg liveweight. Could it be that the skim milk allowed the piglets to compensate and return to their preprogrammed growth curve? Since sow’s milk is known to be deficient in protein for maximum lean gain, skim milk with its high protein content would make an excellent supplement to sow’s milk.

2.9

The importance of weight gain in the first week after weaning

The aim of producers is to encourage piglets to make a smooth transition between drinking milk from the sow and eating solid feed after weaning with minimal interruption to growth. The importance of the rate of growth in the first week after weaning in determining growth to slaughter is shown in calculations made by Pluske et al. (1995). They analysed data from Pollman (1993) showing that if pigs maintained weight during the first week after weaning they reached slaughter weight in 178 days but, if pigs grew at 115 g/d or better in the first week, age at slaughter

26

Weaning the pig


was reduced by 15 days to 163 days. This means that a 0.9 kg weight difference one week after weaning becomes a 12 kg difference in weight at slaughter. Similarly, Tokach et al. (1992) showed that pigs gaining 225 g/d were 1.6 kg heavier at the end of the first week after weaning than pigs that maintained weight and were 8 kg heavier at slaughter at 156 days.

2.10

Minimising the growth check at weaning

The extent and duration of the interruption or growth check is highly variable. Pluske et al. (1995) concluded that it often takes pigs two or even three weeks to recover their energy intake and grow at the same rate as they did before weaning, let alone grow faster to begin to reach their potential. Minimising the growth check at weaning depends on the amount of food the piglet can eat. Fowler and Gill (1989) calculated that if a weaned pig at 21 days of age was to grow at 280 g/d, a growth akin to growth on the sow, it would need to eat 7.8 MJ of DE. Hence, it would need to eat 500 g of a starter diet containing 15.5 MJ of DE, an intake that is never seen under experimental conditions let alone in commercial practice. Campbell (1989) believes that practical nutrition of the young pig at weaning is more of an art than a science and has suggested that a dietary regime that is highly successful and repeatable at a research station may not stand up to the rigours of commercial practice. Such a comment simply reflects the number of factors that impinge and interact on the animal at weaning. However there are some general nutritional principles that have been established as far as nutrition of the young pig is concerned. High food intake and hence high growth rates with minimal digestive disturbances can only be achieved consistently when high-density, highly-digestible diets are used. Starter diets are generally required to ease the transition from milk (high fat, high lactose) to plant based diets that are much lower in fat, and contain high non-starch polysaccharides. Such diets generally need to contain high-quality animal products of milk origin and/or products derived from blood. The younger the pig is at weaning the more important this becomes and this is nicely demonstrated in recent data from Dunshea et al. (2002a). They offered piglets a traditional weaner diet containing wheat (55%), lupins (5%), soybean meal (5%) meatmeal (6.6%), fish meal (8.3%) skim milk (2%) and blood meal (2.6%) and whey powder (10%) and weaned them at either 14 or 24 days of age. The older pigs at weaning coped much better than the younger pigs (Table 2.2) with this sort of diet and gained weight during the first week after weaning while the younger pigs lost weight. In the 1970s it was generally regarded that the most profitable time to wean pigs was between 3 and 5 weeks. During the 1980s this changed and interest was rekindled in weaning pigs earlier largely because of two findings. The first was the realisation that sow’s milk begins to impose a limit on the growth of piglets at about


27

Williams

Table 2.2. Age at weaning and its effect on growth (g/d) after weaning (from Dunshea et al., 2002a). Age at weaning (d) Days after weaning

14

24

0-7 7 - 14 14 - 21

-16 187 333

162 340 460

day 10 of age and, by 3 weeks, the limitation becomes severe enough to reduce piglet growth. Second, piglets at two weeks of age are relatively free of disease and, the longer they stay with the sow, the more disease organisms they are likely to acquire. So early weaning was thought to be a way of reducing and controlling disease and overcoming the limitation of milk imposed by the sow. Successful early weaning requires specialised diets if the growth check at weaning is to be minimised. In the early 1990s, nutritionists at Kansas State University began to develop a dietary program for early weaning to ease the transition from sow’s milk to solid food (see chapter by M. Tokach et al.). The program was based on feeding piglets as soon as they were weaned with milk products and animal plasma proteins. Products from porcine blood, particularly porcine plasma, have now been tested in many studies and seem to be mandatory for diets in North America. It seems that an inclusion rate of 6% is likely to stimulate food intake of young pigs, particularly in situations where enteric disease is more prevalent (Coffey and Cromwell, 2001). The most favoured explanation of the stimulation of food intake is that it is due to the presence of immunoglobulins and presumably immunoglobulins of pig origin might be more effective than those derived from cow’s milk. But, because of the concern about feeding animal proteins to the same species, there is now interest in looking at other sources of immunoglobulins. Products from cows are also effective in stimulating food intake and growth. Pluske et al. (1999) weaned pigs at 4 weeks and found that 5% spray-dried colostrum stimulated food intake by 12% in the first week after weaning. They increased the amount to 10% and stimulated food intake by 25%. This extra food intake boosted growth by 40% and 80% respectively so that pigs on the highest level of colostrum grew in excess of 200 g/d in the first week after weaning, a very acceptable rate of growth. King et al. (2001) have also found a 25% stimulation to food intake in the first week after weaning by adding 6% bovine colostrum. They found a lesser,

28

Weaning the pig


non-significant stimulation with spray-dried bovine plasma. Dunshea et al. (2002b) have recently compared a number of animal products containing immunoglobulins and, rather than using spray-dried products from commercial sources, they freeze-dried their own products to preserve the potency of the immunoglobulins. They compared porcine and bovine plasma, bovine colostrum and commercially produced skim milk and found relatively little difference between the protein sources in the performance of pigs weaned at 14 days. However, they did point out that their studies were conducted in a ‘clean’ research environment. There is little doubt that high-quality animal proteins are far superior at stimulating growth in early-weaned pigs and even small amounts of plant protein will depress performance (see Dunshea et al., 2002b; Liu et al., 2001). Advances in technology have allowed liquid feeding systems to be a viable commercial option and, as a consequence, there is now interest in using liquid milk to stimulate food intake and growth. Pluske et al. (1996a) demonstrated that, given a similar intake, fresh milk obtained from sheep maintained villous height better than a dry diet based on skim milk powder and fish meal. They found that villous height could also be maintained with fresh cow’s milk and the more milk consumed the greater the height of the villi or, alternatively, less villous atrophy (Pluske et al., 1996b). Maintenance of gut architecture after weaning seems a prerequisite for high food intake and good growth, particularly for pigs weaned early in life at two to three weeks of age. So feeding liquid milk or milk replacer at weaning is perhaps the best way of minimising the growth check. Heo et al. (1999) almost eliminated the growth check by feeding a liquid milk replacer at weaning, and they achieved a growth rate of 470 g/d for the first 7 days after weaning pigs at 14. The pigs were held at 24°C in this experiment. When pigs were kept at 17°C, and presumably cold stressed, growth was reduced to 340 g/d and, when kept at 32°C and possibly heat stressed, growth was also reduced to 360 g/d. Kim et al. (2001) have also recorded extremely high growth rates with very young pigs weaned at 11 days of age and fed diets based on whey proteins (70%), lard (12%) and plasma proteins (5%) fed either in liquid form or as a dry pellet. Pigs fed the liquid grew at 380g/d while those fed the pellets grew at 260 g/d for the first 14 days after weaning.

2.11

Does minimising the growth check have longterm benefits?

Minimising the growth check at weaning has obvious short-term benefits of faster turnover in the weaner rooms and reductions in mortality and morbidity but there are very few studies where long-term benefits for growth have been quantified. Dunshea et al. (1997a) found that skim milk fed to pigs for one week after weaning


29

Williams

at 20 days of age increased liveweight by 0.6 kg compared with control animals offered a dry, conventional starter diet. By the time the pigs had reached 120 days of age the difference in weight had increased to 3 kg (59 vs 62 kg). Pluske et al. (1999) fed spray-dried bovine colostrum to pigs and, 14 days after weaning at 4 weeks of age, the weight advantage of the pigs fed colostrum was 1.1 kg. This growth difference was still evident at slaughter at 83 kg. Kim et al. (2001) induced a difference in weight of 1.6 kg 14 days after weaning by feeding pigs a milk replacer diet in a liquid rather than a dry pellet. This difference doubled to 3.3 kg by the time the pigs reached 150 days of age and about 110 kg. So it seems from the few reports available that stimulation of growth in the immediate post-weaning period by highquality animal proteins has a small but beneficial effect on long-term growth. There has been some suggestion that stimulating post-weaning growth and minimising the check is unnecessary because pigs will display compensatory growth and catch up to their contemporaries who have suffered less of a check. Whang et al. (2000) addressed this by comparing a 3-phase starter regimen containing highquality animal products (skim milk, whey, and plasma protein) with a traditional starter diet based on corn and soybean with minimal fish meal. Pigs fed animal protein gained liveweight at 175 g/d while the pigs fed the corn/soybean diet lost 38 g/d, and this gave a difference in liveweight of 1.5 kg at the end of the first week after weaning. Animal protein allowed the pigs to gain substantial amounts of body protein and keep fat losses to a minimum, while the pigs fed plant proteins could only maintain their body protein and they lost substantial amounts of fat (Table 2.3).

Table 2.3. Change in liveweight, body protein and body fat (g/d) in the first 7 days after weaning (from Whang et al., 2000). Diet

Liveweight

Protein

Fat

Animal protein Corn/soybean

175 -38

30 5

-7 -30

Despite these differences created in the first week after weaning the pigs fed the traditional starter diet compensated and reached the same mass of body protein (15.4 vs 15.1 kg) as the pigs fed animal protein at 152 days of age although they did not compensate completely in body fat (25.5 vs 28.1 kg) and were leaner. If body protein had been lost in the first week after weaning rather than just maintained it would be interesting to know whether there would have been complete compensation. Young pigs, particularly after weaning, protect their body protein and appear to preferentially metabolise fat in times of nutritional shortage. Whittemore et al. (1978) showed that for the first week after weaning piglets lost

30

Weaning the pig


a modest 6 g/d of bodyweight and this consisted of a large loss of fat (46 g/d) and gains in both protein (4 g/d) and water (36 g/d). They suggested that young pigs probably needed to grow at rates of about 200 g/d before they started to accumulate body fat. Allowing pigs to exhibit compensatory growth might be one way reducing the cost of starter diets and increasing the efficiency of growth.

2.12

Conclusions

It is suggested that growth and its driver, food intake, are pre-programmed and that bigger animals at birth are bigger at weaning and bigger at maturity. The consequence of this is that a larger animal will grow faster than a smaller animal at any stage of its life. Hence pigs that are heavier at weaning will grow faster than lighter ones and any weight differences at weaning will be magnified during postweaning growth. It seems from most of the evidence that stimulating growth of piglets during lactation to reach a greater weaning weight is rarely rewarded by a higher post-weaning growth. Simple observations on growth rate in the first week after weaning, like the genetically programmed weight at weaning, suggest that this is also an important determinant of post-weaning growth, that is, the more rapid the growth the faster the pig reaches market weight. The normal check in growth that follows weaning can be minimised and reduced to only a few days by feeding high-quality diets based on animal proteins. This circumvents the need for the normal mechanisms of compensatory growth that would otherwise operate and allow animals to catch up to their normal growth path.

References Armstrong, W.D. and A.J. Clawson, 1980. Nutrition and management of early weaned pigs: effects of increased nutrient concentrations and/or supplemental liquid feeding. Journal of Animal Science 50, 377-384. Black, J.L., 1995. Modelling energy metabolism in the pig - critical evaluation of a simple reference model. In: P.J. Moughan, M.W.A. Verstegen, and M.I. Visser-Reneveld (editors), Modelling Growth in the Pig. EAAP Publication No. 78. Wageningen Pers, Wageningen, The Netherlands, pp. 87102. Brown, L.J., G.L. Krebs and B.P. Mullan, 1999. Feeding of liquid milk supplements to pigs preand post-weaning improves live weight gain. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association, Werribee, Victoria, pp. 273. Campbell, R.G., 1989. The nutritional management of weaner pigs. In: J.L. Barnett and D.P. Hennesy (editors), Manipulating Pig Production II. Australasian Pig Science Association: Werribee, pp. 170-175. Campbell, R.G. and A.C. Dunkin, 1982. The effect of birth weight on the estimated milk intake, growth and body composition of sow-reared piglets. Animal Production 335, 193-197.


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McConnell, J.C., J.C. Eargle and R.C. Waldorf, 1987. Effects of weaning weight, co-mingling, group size and room temperature on pig performance. Journal of Animal Science 65, 1202-1206. McCracken, K.J. and D. Kelly, 1993. Development of digestive function and nutrition/disease interactions in the weaned pig. In: D. J. Farrell (editor), Recent Advances in Animal Nutrition in Australia 1993. Department of Biochemistry, Microbiology and nutrition, University of New England, Armidale, Australia, pp. 182-192. Miller, H.M., P. Toplis and R.D. Slade, 1999. Weaning weight and daily live weight gain in the week after weaning predict piglet performance. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association: Werribee, pp. 130. Morgan, J.H.L., 1972. Effect of plane of nutrition in early life on subsequent live-weight gain, carcass and muscle characteristics, and eating quality of meat in cattle. Journal of Agricultural Science 78, 417-423. O’Donovan, P.B., 1984. Compensatory growth in cattle and sheep. Nutrition Abstracts and Reviews (Series B) Livestock Feeds and Feeding 54, 389-410. Pluske, J.R., G. Pearson, P.C.H. Morel, M.R. King, G. Skilton and R. Skilton, 1999. A bovine colostrum product in a weaner diet increases growth and reduces days to slaughter. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association: Werribee, pp. 256. Pluske, J.R., I.H. Williams and F.X. Aherne, 1995. Nutrition of the neonatal pig. In: M.A. Varley (editor), The Neonatal Pig Development and Survival. CAB International, Wallingford, Oxon., pp. 187-235. Pluske, J.R. and I.H. Williams, 1996. Split weaning increases the growth of light piglets during lactation. Australian Journal of Agricultural Research 47, 513-523. Pluske, J.R., I.H. Williams and F.X. Aherne, 1996a. Maintenance of villous height and crypt depth in piglets by providing continuous nutrition after weaning. Animal Science 62, 131-144. Pluske, J.R., I.H. Williams and F.X. Aherne, 1996b. Villous height and crypt depth in piglets in response to increases in the intake of cow’s milk after weaning. Animal Science 62, 145-158. Pollmann, D.S., 1993. Effects of nursery feeding programs on subsequent grower-finisher pig performance. In: J. Martin (editor), Proceedings of the Fourteenth Western Nutrition Conference. University of Alberta, Edmonton, pp. 243-254. Reale, T.A., 1987. Supplemental liquid diets and feed flavours for young pigs. Master of Agricultural Science thesis: University of Melbourne. Ryan, W.J., 1990. Compensatory growth in cattle and sheep. Nutrition Abstracts and Reviews (Series B) Livestock Feeds and Feeding 60, 653-664. Tokach, M.D., R.D. Goodband, J.L. Nelssen and D.R. Keesecker, 1992. Influence of weaning weight and growth during the first week postweaning on subsequent pig performance. In: Proceedings of the American Association of Swine Practitioners University of Minnesota, pp. 409. Toplis, P., P.J. Blanchard and H.M. Miller, 1999. Creep feed offered as a gruel prior to weaning enhances performance of weaned piglets. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association: Werribee, pp. 129. Whang, K.Y., F.K. McKeith, S.W. Kim and R.A. Easter, 2000. Effect of starter feeding program on growth performance and gains of body components from weaning to market weight in swine. Journal of Animal Science 78, 2885-2895.

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Whittemore, C.T. and D.M. Green, 2001. Growth of the young weaned pig. In: M.A. Varley and J. Wiseman (editors), The weaner pig: Nutrition and Management. CAB International, pp. 115. Whittemore, C.T., A. Aumaitre and I.H. Williams, 1978. Growth and body composition in young weaned pigs. Journal of Agricultural Science (Cambridge) 91, 681-692. Widdowson, E.M., and D. Lister, 1991. Nutritional control of growth. In: A.M. Pearson and T.D. Dutson (editors), Growth Regulation in Farm Animals. Advances in Meat Research 7. Elsevier Applied Science, London and New York, pp. 67-101. Williams, I.H., 1976. Nutrition of the young pig in relation to body composition. PhD thesis, University of Melbourne. Williams, I.H., 1995. Sow’s milk as a major nutrient source before weaning. In: D.P. Hennessy and P.D. Cranwell (editors), Manipulating Pig production V. Australasian Pig Science Association: Werribee, pp. 107-113. Wolter, B.F. and M. Ellis, 2001. The effects of weaning weight and rate of growth immediately after weaning on subsequent pig growth performance and carcass characteristics. Canadian Journal of Animal Science 81, 361-369. Wolter, B.F., M. Ellis, B.P. Corrigan and J.M. DeBecker, 2002. The effect of birth weight and feeding of supplemental milk replacer to piglets during lactation on preweaning and postweaning growth performance and carcass characteristics. Journal of Animal Science 80, 301-308.


35

3

Nutritional management of the pig in preparation for weaning R.H. King and J.R. Pluske

3.1

Introduction

The average weaning age in many of the major pork-producing countries in the world has declined progressively over the last 20 years owing to the continued pressure on the pig industry to improve the efficiency of pork production. Reducing the age at weaning to 18 to 24 days of age, which is the average weaning age in many countries, has the potential of improving efficiency. This is because the farrowing interval of sows is reduced (thereby increasing the number of pigs produced per sow per year) and the risk of disease transfer between sows and piglets (segregated early weaning systems) is reduced, thereby increasing growth rate and efficiency in subsequent growth phases. Removing piglets from the sow at an earlier age also provides opportunities to exploit the enormous growth potential of the young pig, because it is well established that the sucking piglet, because of limitations on sow milk yield and milk composition, does not grow to its full genetic potential. Weaning can be regarded as one of the most critical periods in the modern-day pork production cycle because it represents a period of adaptation and stress in response to the simultaneous stressors imposed on pigs at weaning. Pigs are removed from their mothers, usually mixed with others and moved to a different environment, and are fed an alien diet that is presented and offered very differently to sows’ milk that was received during lactation. Consequently, pigs usually suffer a post-weaning “growth check” for 7-14 days following weaning that is characterised by low and variable feed intake, poor and variable growth rate, increased maintenance requirements and increased susceptibility to enteric pathogens to cause diseases such as post-weaning colibacillosis. There is now realisation that the weight of the pig at weaning, and indeed at birth, bears a strong, positive relationship to subsequent growth and weight at some point in the future. A key performance target in pork production should be maximisation of weaning weight, because this will have an overall influence on subsequent growth in the growing and finishing stages. Also of importance is the variation in weaning weight, and weight in the nursery, grower and finisher phases. Increases in litter size cause an increase in variation in piglet size, and this includes more piglets in the less viable category. Limiting weight variation is important for improving a facility’s utilisation of all-in, all-out systems, and this needs to be balanced against management strategies aimed at improving piglet growth rate during lactation.


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The influences of sow-and piglet-related characteristics to milk production by the sow have been the subject of many reviews (eg, Hartmann and Holmes, 1989; Pettigrew, 1995; Williams, 1995; Le Dividich, 1999), and will not be discussed in this chapter. To help satisfy the requirements of the piglet to achieve maximum growth potential and maximum weaning weight, nutrients additional to those supplied by sow’s milk are often provided to the sucking pig. In addition, the supply of additional nutrients may also prepare the digestive system of the sucking pigs to cereal-based solid diets after weaning. The purpose of this chapter is to discuss some of the management options available before weaning to ensure that the liveweight of the pig, and perhaps the efficiency of the gastrointestinal tract, is maximised/optimised at weaning so that the stressors imposed around weaning will have less impact upon overall efficiency in the production system.

3.2

The importance of weaning weight to subsequent growth

The weight of piglets at weaning is one of the most critical factors determining the subsequent growth performance of pigs, and has been reviewed in chapter 14 (Le Dividich et al., 2003). Research by Campbell (1990), for example, showed a strong inverse relationship between weight of pigs at weaning at 28 days of age (W) and the length of time taken to grow to 20 kg live weight (T), as follows: T = 52.1 (± 1.69) - 3.39 (± 0.224) W (R2 = 0.85, P < 0.001). Based upon this equation, pigs that are 1 kg heavier at weaning reach 20 kg over 3 days earlier. Other research using younger pigs (eg, Dritz et al. 1996; Miller et al. 1999) confirms this general relationship. Heavier pigs at weaning seem to continue their weaning weight advantage to slaughter weight (Mahan and Lepine, 1991; Le Dividich et al. 2003), and the age at slaughter could be reduced even further by at least 10 days for a pig that is 1 kg heavier at weaning (Cole and Close, 2001). Because of the positive relationship between weaning weight and post-weaning growth performance, any factor that increases piglet weight at weaning should reduce slaughter age. Interestingly, data from both commercial and research trials shows consistently that there is a highly significant (30 to 60% of the total variance) effect of litter from which the piglet is derived on weaning weight and subsequent post-weaning performance (Slade and Miller, 1999). This indicates that one or more factors that occurs prior to weaning is/are having a major influence on both weaning weight and subsequent growth rate, with both pre-natal and post-natal components having an effect. Rooke et al. (1998) reported that the relative importance of these events

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Weaning the pig

Nutritional management of the pig in preparation for weaning

was 3:1 in favour of the pre-natal effects, begging the question of just where exactly does one begin to investigate the phenomenon of variation in pig weights. Some authors (Bate, 1991; Braastad, 1998) have presented evidence of in utero effects on subsequent post-natal behaviour. Nevertheless, maximisation of weaning weight should remain a goal in pig production because of its relationship to the number of days it takes a given pig to reach slaughter weight.

3.3

Nutrient intake before weaning

The piglet places an enormous reliance on the sow for its nutritional needs before weaning, first consuming colostrum in the first 24-36 hours after parturition and then consuming milk at regular intervals during the day and night until weaning (Pluske and Dong, 1998). The intake of an ‘adequate’ amount of colostrum before closure of the small intestine to immunoglobulins is of crucial importance to both the subsequent survival and performance of the young pig (Le Dividich and Noblet, 1981; Varley, 1992). Coalson and Lecce (1971) considered an intake of 40-60 g colostrum was necessary for piglets to have normal serum immunoglobulin concentrations. The provision of colostrum to weaker piglets, or to litters where the sow is suffering agalactia, is generally used as a key management technique to increase survival rates, increase weaning weight, and possibly reduce the variation in weaning weight. Alternatively, practices such as split weaning immediately after farrowing offer potential to allow a more equitable transfer of colostral immunoglobulins across the spectrum of weights within a litter (Donovan and Dritz, 1997). Many studies espouse the benefits of colostrum for gut development, as an energy source for thermoregulation of the newborn piglet, a substrate for protein synthesis, and as a passive supply of protection against enteric pathogens. Collectively, these functions are important in establishing the pig during lactation and, ultimately, after weaning. 3.3.1

Supplying creep food in lactation

Amongst the many pre-weaning influences that can affect the growth and survival of pigs after weaning, most attention has been directed towards the nutrition of the young pig. A plethora of studies have examined, and reviewed, the effects of creep feeding (ie, offering a solid diet) during lactation on weaning weight and performance thereafter (eg, Pluske et al., 1995). This is based largely on the premise that offering solid feed before weaning will familiarise, both behaviourally and physiologically, the young pig to the changes imposed on it simultaneously at weaning. Traditionally, the sucking piglet has been supplied with creep food for two main reasons. First, creep food supplies supplemental nutrients that are required to maintain satisfactory growth rates and achieve heavier weaning weights. Second, the consumption of creep food is believed to prepare the digestive system of the


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piglet for digestion of complex carbohydrates and protein that will be supplied as the sole source of nutrients after weaning. However, some research, such as that of Chapple et al. (1989), found that the variation in amylolytic activity in the pancreas of piglets was more a function of sow (litter of origin) than of the intake of solid feed during lactation and immediately after weaning. Similarly, it has been reported that pepsin and maltase activities could not be related to weaning weight or creep feeding time (Lindemann et al. 1986; de Passille et al. 1989). 3.3.2

Dry creep feed intake

Evidence to support the notion that supplying pigs with dry creep food during lactation will improve pre-weaning growth performance is equivocal. Pluske et al. (1995) reviewed a large number of studies presented in the literature and found an enormous variation in feed intake of creep-fed piglets, with the contribution of creep feed to daily energy intake prior to weaning at 21-35 days of age ranging from 1.2 to 17.4%. Thus the data from the literature demonstrate that intake of dry creep food during lactation is generally small and variable and unlikely to significantly influence weaning weight, particularly in piglets weaned at 3 weeks of age or younger. Furthermore, growth rate in the immediate period following weaning is often poorly related to pre-weaning creep food intake (Barnett et al. 1989, Pajor et al. 1991; Fraser et al. 1994), suggesting that causal links between creep feeding and weight gain after weaning remain to be demonstrated. Two of the reasons for this are because creep feed consumption varies so much within litters and between litters. Fraser et al. (1994), for example, estimated that creep feed intake (associated with creep feeding behaviour) accounted for only 1-4% of the variation in liveweight gain in piglets in their first 14 days following a 28-day weaning, even though there were significant litter effects on the intake of dry feed during lactation. Nevertheless, some pork producers, especially those weaning later than 21 days of age, often offer high-quality expensive creep diets to sucking pigs, despite minimal responses in pre-weaning growth rate, to assist the adaptation to starter diets as the sole source of nutrients immediately after weaning. In some European countries such as Sweden and Denmark where weaning age is now 28 days of age or greater, and the use of growth-promoting antibiotics and antimicrobial agents such as zinc oxide are banned or strictly regulated, the importance of enhancing the intake of solid feed before weaning is receiving renewed attention. This is to take advantage of both a heavier weaning weight and to modulate the gastrointestinal tract, especially the microflora, to the dietary challenges after weaning. Numerous recent studies, such as those reported by Toplis et al. (1999) and Blanchard et al. (2000), show that offering creep feed as a gruel/slurry (1:2 meal to water) may enhance the consumption of dry matter before weaning.

40

Weaning the pig


3.3.3

Liquid diets to enhance feed intake

In contrast to the equivocal results reported with dry creep feed supplementation (Pluske et al. 1995), providing sucking piglets with liquid diets would appear to offer more potential to provide a significant boost to pre-weaning growth rate and weaning weight (Reale, 1987; Azain et al. 1996), and also performance after weaning (see Odle and Harrell, 1998, for review). Reale (1987) offered cows’ whole milk to piglets from 10.00 h each day, adding fresh milk every two hours until 23.00 h, from day 7 to day 28 of lactation. Growth was stimulated by 151 g/day (71%) in the fourth week of lactation and, from days 7 to 28, by 87 g/day, an amount that increased weaning weight by 1.8 kg in comparison to controls that were offered a dry creep feed. Similarly, King et al. (1998) found that piglets offered cows’ liquid milk from day five of lactation were 1.6 kg heavier at weaning at 28 days of age than piglets which received no supplemental nutrients. In addition, piglets appeared to still prefer milk from the sow, as the supply of supplemental milk did not reduce the amount of milk that the piglet obtained directly from the sow. The results of a number of studies where sucking piglets were offered milk liquid diets are shown in Table 3.1. Significant increases in the intakes of nutrients have been observed when sucking pigs have been offered liquid milk diets compared to dry creep intakes (Table 3.1). As a result, pre-weaning growth rates are increased by 11 to 35% (Table 3.1). These results demonstrate the potential benefit of additional nutrients on weaning weight and a clear benefit of supplemental milk replacer to increase weaning weight. Although pre-weaning growth rates were increased to almost 300 g/day, there is still enormous potential for these piglets to grow faster up until weaning at 21-28 days of age (Hodge, 1974) if further nutrients are consumed. The use of a liquid milk replacer not only before weaning, but the supply of liquid diets during the immediate period after weaning, can further reduce the growth check and improve the subsequent growth performance of pigs. Kim et a1. (2001) showed that feeding a starter diet as a liquid rather than in the dry form for the first 14 days after weaning significantly increased weight at 28 days of age by 1.62 kg. In this study, pigs were weaned at 14 days of age. This growth advantage was maintained to market weight with no evidence of compensatory gain in the dryfed control pigs. However, and in contrast, Lawlor et al. (2002) showed no positive effects whatsoever on post-weaning gain when a number of dietary interventions based on liquid feeding were implemented after weaning. Dunshea et al. (1997) attempted to alleviate the post-weaning growth check by providing extra milk around the time of weaning. Pigs provided with liquid milk replacer, in addition to access to dry starter feed, gained 1.2 kg during the first week after weaning whereas pigs that received only dry starter feed gained 0.4 kg in the


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Table 3.1. Consumption of liquid milk replacer by piglets during lactation and consequent growth response. Reference

Treatment duration of feeding (days)

Azain et al. (1996) Cool season No replacer 21 Replacer 21 Warm season No replacer 21 Replacer 21 King et al. (1998) No replacer 24 Replacer 24 Dunshea et al. (1997b) No replacer 10 Replacer 10 Campbell (1990) No replacer 10 Replacer 10 Pluske et al. (1995)1 15.3 1Means

Lactation length (days)

Average Pre-weaning Increase in supplemental growth rate growth rate intake over (g/day) (%) lactation (g DM/pig/day)

21 21

20.9

222 247

11

21 21

66.2

166 224

35

28 28

58.5

238 297

25

20 20

48.5

223 291

30

28 28 28.1

29.3 11.8

214 264 213.6

23

figures for dry creep intake in studies reviewed by Pluske et al. (1995).

first week after weaning (Dunshea et al. 1997). Supply of a liquid milk replacer to piglets both prior to weaning and in the first week after weaning had an additive effect; pigs that received liquid milk replacer before and after weaning were 10% heavier at 120 days of age than pigs that were suckled by the sow only and weaned onto dry starter feed (Dunshea et al. 1997). Much of this improvement was due to the extra nutrient intake from supplemental milk replacer prior to and immediately after weaning. The development of liquid feeds and feeding systems offers the potential to markedly improve the growth performance of piglets both before weaning and during the immediate period after weaning.

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3.3.4

The effects of gender on nutrient intake of neonatal pigs

An interesting observation by King et al. (1998) was that female piglets grew faster than their male counterparts prior to weaning when litters were offered supplemental milk. This was most likely related to greater nutrient intake in the female pigs. Similar observations of greater growth rates amongst female piglets have been made in the immediate post-weaning period when pigs were offered either liquid diets (Dunshea et al. 1997) or dry diets (Bruininx et al. 2001; Dunshea et al. 2001). In a retrospective analysis of 58 studies conducted at the University of Kentucky, Cromwell et al. (1996) showed that gilts grew more rapidly over the first few weeks after weaning. Thus, there does appear to be more sexual dimorphism in young pigs, and this is often manifested in the immediate post-weaning period if nutrient intake is high or when supplemental nutrients are provided before weaning.

3.4

The composition of diets offered during lactation

During the first two or three weeks of life, the piglet’s digestive tract is best suited to digest lactose, fat and the milk proteins, casein and whey (Pluske and Dong, 1998). The digestive enzymes necessary for the digestion of starch, sugar and nonmilk proteins are present at relatively low levels. Therefore, dry and liquid creep feeds must be palatable, concentrated and contain ingredients compatible with the digestive system of the young sucking pig. Complete creep diets containing cooked or flaked cereals, oils, various milk products and other highly digestible feedstuffs are often used to stimulate food intake of piglets prior to weaning to achieve heavier weaning weights and to prepare the piglet for weaning. Fraser et al. (1994) compared a standard creep diet based primarily on corn and soybean meal with a complex commercial creep diet containing no soybean meal, and found that piglets consumed more of the complex creep diet and were 0.3 kg heavier at weaning at four weeks of age. However, Fraser et al. (1994) found that these piglets only tended to gain more weight in the week before, and the two weeks following, weaning. In other studies with 4- or 5-week weaning, performance of pigs after weaning that have been raised with or without creep feeding has generally shown small or negligible effects (Okai et al. 1976; Barnett et al. 1989; Tokach et al. 1990), although English et al. (1980) showed large effects of pre-weaning creep feed intake on post-weaning performance. One of the contentious issues associated with creep feeding is to do with the inclusion of antigenic compounds, such as glycinin and β-conglycinin from soybean products, in the diet. It has been hypothesised by some researchers that a short-term exposure to creep feed and low feed consumption may sensitise the


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pig to antigens in certain feed ingredients, eg, soybean meal, beans, such that exposure of the sensitised pigs to an increased intake of the same dietary antigens after weaning gives rise to a hypersensitivity response. This, in turn, is believed to cause post-weaning diarrhoea (eg, Miller et al. 1984; Newby et al. 1985). It is outside the scope of this chapter to discuss this issue in detail, however numerous authors have subsequently failed to endorse this hypothesis. For example, Barnett et al. (1989) examined the effects of feeding a common corn-soybean meal-whey creepdiet on the immune response and post-weaning performance of pigs weaned at 4 weeks of age. Although creep-fed pigs tended to have higher immune responses and slightly more severe scouring, both pre-weaning and post-weaning growth performance of piglets were unaffected by the provision of the creep diet containing soybean meal. Similarly, Kelly et al. (1990) found that offering creep feed before weaning failed to affect the prevalence or severity of diarrhoea induced experimentally by exposure to an enteropathogenic strain of Escherichia coli, and Sarimento et al. (1990) reported that restricted feeding of a creep diet failed to affect the incidence of induced diarrhoea and did not induce any morphological changes characteristic of an allergic reaction in the small intestine. McCracken et al. (1999) postulated that any effects of soybean antigens on the structure and function of the small intestine might occur secondarily to the period of starvation that occurs after weaning. The reader is directed towards reviews by Dreaù and Lallès (1999) and Bailey et al. (2001) for further information on this topic. Nevertheless, withholding soybean meal from the diet of a young pig after weaning, to allow for the negative effects on gut structure and function that occur post-weaning, and then re-including it two weeks after weaning, causes the same histological and performance setback as if the antigens were present in the diet all along (Dritz et al., 1996). In this regard, commercial practice dictates that soybean meal is included in diets for young pigs despite the documented physiological, immunological and morphological changes that occur. 3.4.1

Dietary formulation of creep diets

There is a dearth of data relating to the protein and amino acid requirements of pigs before 3-4 weeks of age (ARC, 1981). Data from milk-fed pigs have provided estimates of 0.87 to 0.95 g lysine/MJ gross energy as the nutrient requirements for pigs averaging 4 kg live weight (Williams, 1976, Auldist et al. 1997). There is little data on which to base nutrient requirements for solid diets for weaned pigs. NRC (1998) estimated the minimum dietary requirements of weaned pigs from 3 to 5 kg were 14.2 MJ DE/kg, 18.3g CP/MJ DE and 1.06 g lysine/MJ DE. Similarly, ARC (1981) provided tentative recommendations of 16 g CP/MJ DE and 1.12 g lysine/MJ DE for the nutrient requirements of weaned pigs between birth and three weeks of age.

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Weaning the pig


These dietary requirements are often used as a guide to develop diet specifications for supplemental creep diets. However, the emphasis on dietary formulation of creep diets is more specifically on the choice of palatable and highly digestible protein and energy sources that promote high feed intake rather than meeting the nutrient specifications on a least cost basis. Examples of the composition of creep diets suitable for suckling pigs up until 3-4 weeks of age are shown in Table 3.2 (A.C. Edwards, personal communication). 3.4.2

Use of flavours in creep/starter diets

Attempts have been made to increase weaning weight and reduce the growth check of pigs after weaning by using various sweeteners and aromatic compounds to increase feed consumption, particularly during the first week or two after weaning (Campbell, 1976; Kornegay, 1977). Gatel and Guion (1990) found that diets containing monosodium glutamate significantly increased creep food intake, although the increase was not sufficient to improve weaning weight. However, Clarke and Batterham (1989) found that creep food intake was low and unaffected by the supplementation of a creep diet with monosodium glutamate. Campbell (1976) found that incorporation of a feed flavour into a creep diet failed to increase creep food consumption or weaning weight. However, Campbell (1976) also found that pigs that had been weaned from sows given a flavoured diet and had also been given a flavoured diet after weaning consumed more feed, particularly in the first two weeks after weaning. King (1979) later confirmed this interaction for feed intake after weaning, and also demonstrated that when the flavour was added to the sow diet, it was detected in milk samples collected from those sows. Madsen (1977) indicated that feed preferences could be transferred from lactating sows to their litter by incorporating a non-metabolisable substance into both the lactating sow diet and the diet offered to piglets after weaning. Any positive effects of feed flavours observed in young pigs are more likely to be due to this transference of feed preferences via flavours incorporated in sows milk or masking unacceptable tastes to improve the palatability in the creep diet. 3.4.3

Presentation of the creep diet

One of the most important factors stimulating piglets to eat creep feed is the freshness of the feed. Piglets should be offered small amounts of feed, at least on a daily basis, as not only does this ensure that the feed is fresh, but the frequent arrival of fresh feed stimulates the inherent curiosity of the piglets, thereby encouraging consumption of creep feed (Pajor et al. 1991). Creep feed is usually offered to pigs when they are at least one week of age because they usually show no interest in supplemental dry feed during the first week of


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Table 3.2. Composition of creep diets (g/ kg air dry diet)1. Weaning age

2 weeks

3-4 weeks

Duration of Feeding

2-4 weeks of age

3-6 weeks of age

Diet

1

2

3

4

5

6

Wheat Dehulled oats Extruded corn Soyabean meal Sugar Full fat soyabean meal Meat and bone meal Fish Meal Blood Meal Skim milk powder Whey powder

390 30 30 60 30 50 15 200 150

464 30 40 25 50 20 200 150

352 35 30 119 30 60 200 150

592 80 20 45 55 70 20 100

616 80 20 45 50 60 20 100

579 80 20 79 42 50 20 100

Vegetable oil Dicalcium phosphate Limestone Lysine -HCL D, L-methionine Threonine Tryptophan Mineral/ vitamin premix Salt Digestible energy (MJ/ kg) Crude protein Lysine Methionine Threonine Calcium Phosphorus

38 2 0.5 1.0 0.7 0.2 2.0 -

15 2 0.6 0.6 0.8 0.2 2.0 -

20 0.2 1.0 0.4 0.2 2.0 -

10 2.6 0.8 1.0 0.2 2.0 1.0

2 2 0.6 0.9 0.1 2.0 1.0

5 1.9 1.0 0.4 0.1 2.0 2.0

16.0 233 15.9 5.5 10.1 9.4 7.9

16.1 225 16.1 5.1 10.2 9.1 7.8

16.1 236 16.2 5.8 10.2 9.1 7.6

15.3 229 15.0 4.8 9.5 9.2 7.7

15.6 228 15.3 4.6 9.7 9.4 7.6

15.6 230 15.3 4.9 9.7 9.1 7.3

1Use

of cooked cereals and extruded feed ingredients may improve digestibility. In addition, use of supplements such as organic acids, enzymes and flavours might also improve digestibility, feed intake and (or) piglet health.

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Weaning the pig


life. Initially, feed should be offered on the floor of the farrowing crate or in shallow trays (English et al. 1977). When the litter is obviously consuming the feed, a small feeder allowing room for several piglets to feed at the same time can be used to supply the creep diet to the suckling pigs. Appleby et al. (1991) observed that although provision of fresh food daily compared to three times per day had no effect on creep food consumption, increasing the number of feeding spaces enhanced overall creep intake in both the third and fourth week of lactation. It seems that provision of sufficient feeder space to allow several pigs to feed at once may assist imitation of feeding behaviour, which is an important factor in the establishment of feeding behaviour in pigs (Appleby et al. 1991).

3.5

Water for suckling pigs

Water intake by pigs is often taken for granted but is one of the more critical nutrients, particularly for the sucking pig. Apart from water required to support the growth of muscle tissue and to clear wastes from the body, young pigs require water to replace that lost by evaporation and respiration. Under most circumstances the amount of water consumed via sows’ milk would be more than enough to satisfy the requirements for tissue deposition and evaporative moisture loss (Fraser et al. 1993). Supplemental water is often available to piglets in farrowing crates, but B. Jennings (personal communication) showed that deprivation of supplemental water to suckling piglets had no significant effect on their growth performance to weaning or in the immediate post-weaning period. Water availability is likely to be only important for an underfed piglet in a very warm environment or in a piglet suffering diarrhoea (Fraser et al. 1993).

3.6

Conclusions

The first weeks after weaning are regarded as some of the most crucial in the pork production cycle because they represent a period of adaptation and stress on the young pig. There are nutritional strategies that can be implemented before, and around, weaning to reduce the amount of stress and severity of the growth check in the immediate post-weaning period. Adequate intake of supplemental nutrients before weaning can assist in preparing the digestive system of the pig for the digestion of complex carbohydrates and proteins, and promote greater weight gain and weaning weight. Responses to this strategy, however, tend to be variable and depend to a degree on the weaning age. Supplementation of piglets before and around weaning with liquid milk diets offers the greatest potential to stimulate pre-weaning growth rate and to eliminate the post-weaning check than usually occurs in commercial pork production. The development of liquid feeds and feeding systems offers the potential to prepare the piglet for the weaning process and markedly improve the performance of the young pig.


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References Agricultural Research Council, 1981. The Nutrient Requirements of Pigs. Commonwealth Agricultural Bureau, Slough, UK. Appleby M.C., E.A. Pajor and D. Fraser, 1991. Effects of management options on creep feeding by piglets. Animal Production 53, 361-366. Auldist, D.E., F.L. Stevenson, M.G. Kerr, P. Eason and R.H. King, 1997. Lysine requirements of pigs from 2 to 7kg live weight. Animal Science 65, 501-507. Azain, M.J., T. Tomkins, J.S. Sowinski, R.A. Arentson and D.E. Jewell, 1996. Effect of supplemental pig milk replacer on litter performance: Seasonal variation in response. Journal of Animal Science 74, 2195-2202. Bailey, M., M.A. Vega-Lopez, H.-J. Rothkötter, K. Haverson, P.W. Bland, B.G. Miller and C.R. Stokes, 2001. Enteric immunity and gut health. In: M.A. Varley and J. Wiseman (editors), The Weaner Pig Nutrition and Management. CABBI Publishing, Wallingford, UK, pp. 207-222. Barnett, K.L., E.T. Kornegay, C.R. Risley, M.D. Lindemann and C.R. Schurig, 1989. Characterisation of creep feed consumption and its subsequent effects on immune response, scouring index and performance of weaning pigs. Journal of Animal Science 67, 2698-2708. Bate, L.A., 1991. Modifications in the aggressive and ingestive behaviour of the neonatal piglet as a result of prenatal elevation of cortisol in the dam. Applied Animal Behavioural Science 30, 299-306. Blanchard, P.J., P. Toplis, L. Taylor and H.M. Miller, 2000. Liquid diets fed prior to weaning enhance performance of weaned piglets. In: Proceedings of the British Society of Animal Science, p. 119. Braastad, B.O., 1998. Effects of prenatal stress on behaviour of offspring of laboratory and farmed mammals. Applied Animal Behavioural Science 61, 159-180. Bruininx, E.M.A.M., C.M.C. van der Peet-Schwering, J.W. Schrama, P.F.G. Vereijken, P.C. Vesseur, H. Everts, L.A. den Hartog and A.C. Beynen, 2001. Individually measured feed intake characteristics and growth performance of group-housed weanling pigs. Effects of sex, initial body weight and body weight distribution within groups. Journal of Animal Science 79, 301308. Campbell, R.G. 1976. A note on the use of a feed flavour to stimulate feed intake of weaner pigs. Animal Production 23, 417-419. Campbell, R.G., 1990. The nutrition and management of pigs to 20 kg liveweight. In: Pig Rations: Assessment and Formulation, Proceedings of the Refresher Course for Veterinarians. 132. Post Graduate Committee in Veterinary Science, University of Sydney, pp 123-126. Chapple, R.P., J.A. Cuaron and R.A. Easter, 1989. Effect of glucocorticoids and limited nursing on the carbohydrate digestive capacity and growth rate of piglets. Journal of Animal Science 67, 2956-2973. Clarke, W.A. and E.S. Batterham, 1989. Monosodium glutamate as a flavour enhancer in creepweaner diets for piglets. In: J.L. Barnett and D.P. Hennsessy (editors), Manipulating Pig Production. Australasian Pig Science Association: Werribee, p.184. Coalson, J.A. and J.G. Lecce, 1973. Influence of nursing intervals on changes in serum protein (immunoglobulin) in neonatal pigs. Journal of Animal Science 36, 381-385.

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Cole, D.J.A. and W.H. Close W.H., 2001. The modern pig setting performance targets. Animal Talk 8, 3. Cromwell, G.J., R.D. Coffey, D.K. Aaron, M.D. Lindemann, J.L. Pierce, H.J. Monegue, V.M. Rupard, D.E. Cowen, M.B. Parido and T.M. Clayton, 1996. Differences in growth rate of weaning barrows and gilts. Journal of Animal Science 74 (Suppl. 1), 320. de Passille, A.M.B., G. Pelletier, J. Menard and J. Morrisset, 1989. Relationships of weight gain and behavior to digestive organ weight and enzyme activities in piglets. Journal of Animal Science 67, 2921-2929. Donovan, T.S. and S.S. Dritz, 1997. Effects of split nursing management on growth performance in nursing pigs. American Association of Swine Practitioners, 255-259. Dréau, D. and J.P. Lallès, 1999. Contribution to the study of gut hypersensitivity reactions to soybean proteins in preruminant calves and early-weaned piglets. Livestock Production Science 60, 209218. Dritz, S.S., R.D. Goodband, M.D. Tokach and J.L. Nelssen, 19996. Nutrition programs for segregated early-weaned pigs. Compendium on Continuing Education for the Practicing Veterinarian 18 (Suppl.), S222-S234. Dunshea, F.R., 2001. Sexual dimorphism in growth of sucking and growing pigs. Asian-Australasian Journal of Animal Science 14, 1610-1615. Dunshea, F.R., P.J. Eason, D.J. Kerton, L. Morrish, M.L. Cox and R.H. King, 1997. Supplemental milk around weaning can increase live weight at 120 days of age. In: P.D. Cranwell (editor), Manipulating Pig Production VI. Australasian Pig Science Association: Werribee, p.68. English, P.R., C.M. Robb and M.F.M. Dias, 1980. Evaluation of creep feeding using a highly-digestible diet for litters weaned at 4 weeks of age. Animal Production 30, 496 (Abstr.). English, P.R., W.J. Smith and A. MacLean, 1977. The sow: improving her efficiency. Farming Press, Ipswich. Fraser, D., J.F.Patience, P.A. Phillips and J.M. McLeese, 1993. Water for piglets and lactating sows: Quantity, quality and quandaries. In: D.J.A. Cole, W. Haresign and P.C. Gainsworthy (editors), Recent Developments in Pig Nutrition 2. Nottingham University Press, Loughborough, UK, pp.201-224. Fraser, D., J.J.R. Feddes and E.A. Pajor, 1994. The relationship between creep feeding behaviour of piglets and adaptation to weaning. Effect of diet quality. Canadian Journal of Animal Science 74, 1-6. Gatel, F. and P. Guion, 1990. Effect of monosodium L glutamate on diet palatability and piglet performance during suckling and weaning periods. Animal Production 50, 365-372. Hartmann, P.E. and M.A. Holmes, 1989. Sow lactation. In: J.L. Barnett and D.P. Hennessy (editors), Manipulating Pig Production VI. Australasian Pig Science Association, Werribee, Victoria, pp. 72-97. Hodge, R.W., 1974. Efficiency of food conversion and body composition of the pre-ruminant lamb and young pig. British Journal of Nutrition 32, 113-126. Kim, J.H., K.N. Heo, J. Odle, I.K. Han and R.J. Harrell, 2001. Liquid diets accelerate the growth of easily weaned pigs and the effects are maintained to market weight. Journal of Animal Science 79, 427-434.


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King, R.H., 1979. The effect of adding a feed flavour to diets of young pigs before and after weaning. Australian Journal of Experimental Agriculture and Husbandry 19, 695-697. King, R.H., J.M. Boyce and F.R. Dunshea, 1998. The effect of supplemental nutrients on the growth performance of suckling pigs. Australian Journal of Agricultural Science. 49, 1-5. Kornegay, E.T., 1977. Artificial sugar replacers whey intensifier, aromatic attractants for swine starter rations. Feedstuffs 49 (48), 24. Kelly, D., J.J. O’Brien and K.J. McCracken, 1990. Effect of creep feeding on the incidence, duration and severity of post-weaning diarrhoea in pigs. Research in Veterinary Science 49, 223-228. Lawlor, P.G., Lynch, P.B., Gardiner, G.E., Caffrey, P.J., O’Doherty, J.V., 2002. Effect of liquid feeding weaned pigs on growth performance to harvest. Journal of Animal Science 80, 1725-1735. Le Dividich, J., 1999. Neonatal and weaner pig: Management to reduce variation. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association, Werribee, Victoria, pp. 135-156. Le Dividich, J. and J. Noblet, 1981. Colostrum intake and thermoregulation in the neonatal pig in relation to environmental temperature. Biology of the Neonate 40, 167-174. Lindemann, M.D., S.G. Cornelius, S.M. El Kandelgy, R.L. Moser and J.E. Pettigrew, 1986. Effect of age, weaning and diet on digestive enzyme levels in the piglet. Journal of Animal Science 62, 1298-1307. Madsen, F.C., 1977. Development of feed preference in young swine. Feedstuffs 49 (5), 25. Mahan, D.C. and A.J. Lepine, 1991. Effect of pig weaning weight and associated nursery feeding programs on subsequent performance to 105 kilograms body weight. Journal of Animal Science 69, 1370-1378. McCracken, B.A., M.E. Spurlock, M.A. Roos, F.A. Zuckerman and H.R. Gaskins, 1999. Weaning anorexia may contribute to local inflammation in the piglet small intestine. Journal of Nutrition 129, 613-619. Miller, B.G., A.D. Phillips, T.J. Newby, C.R. Stokes and F.J. Bourne, 1984. Immune hypersensitivity and post-weaning diarrhoea in the pig. Proceedings of the Nutrition Society 43, 116A. Miller, H.M., P. Toplis and R.D. Slade, 1999. Weaning weight and daily live weight gain in the week after weaning predict piglet performance. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association, Werribee, Victoria, p. 130. National Research Council. 1998. Nutrient Requirements of Swine. 10th Edition. National Academy Press, Washington, DC. Newby, T.J., B.G. Miller, D,J. Hampson and F.J. Bourke, 1985. Local hypersensitivity response to dietary antigens in early weaned pigs. In: D.J.A. Cole and W. Haresign (editors), Recent Developments in Pig Nutrition. Butterworths, London. Odle, J. and R.J. Harrell, 1998. Nutritional approaches for improving neonatal piglet performance: Is there a place for liquid diets in commercial production? A review. Asian-Australasian Journal of Animal Science 11, 774-780. Okai, D.B., F.X. Aherne and R.T. Hardin, 1976. Effects of creep and starter composition on feed intake and performance of young pigs. Canadian Journal of Animal Science 56, 573-586. Pajor, E.A., D. Fraser and D.L. Kramer, 1991. Individual variation in the consumption of solid food by suckling pigs and its relationship to post-weaning performance. Applied Animal Behaviour Science 32, 139-155.

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Pettigrew, J.E., 1995. The influence of substrate supply on milk production in the sow. In: D.P. Hennessy and P.D. Cranwell (editors), Manipulating Pig Production V. Australasian Pig Science Association, Werribee, Victoria, pp. 101-106. Pluske, J.R. and G.Z. Dong, 1998. Factors influencing the utilisation of colostrum and milk. In: M.W.A. Verstegen, P.J. Moughan and J.W. Schrama (editors), The Lactating Sow. Wageningen Pers, Wageningen, pp. 45-70. Pluske, J.R., I.H. Williams and F.X. Aherne (1995). Nutrition of the neonatal pig. In: M.A.Varley (editor), The Neonatal pig - Development and Survival. CAB International, Wallingford, UK, pp. 187-235. Reale, J.A., 1987. Supplemental liquid diets and feed flavours for young pigs. M. Agr. Sc. Thesis, University of Melbourne. Rooke, J.A., M. Shanks and S.A. Edwards, 1998. Maternal and dietary influences on post-weaning piglet growth. In: Proceedings of the British Society of Animal Science, p. 156. Sarimento, J.I., P.L. Reinnels and H.W. Moon, 1990. Effects of pre-weaning exposure to a starter diet on enterotoxigenic Escherichia coli - induced post weaning diarrhoea in swine. American Journal of Veterinary Research 51, 1180-1183. Slade, R.D. and H.M. Miller, 1999. Influences of litter origin and weaning weight on post-weaning piglet growth. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association, Werribee, Victoria, p. 131. Tokach, M.D., J.E. Pettigrew, L.J. Johnston and S.G. Cornelius, 1990. Overall performance to market weight is improved by adding milk products, but not fat to the starter diet. Journal of Animal Science 68 (Suppl. 1), 377. Toplis, P., P.J. Blanchard and H.M. Miller, 1999. Creep feed offered as a gruel prior to weaning enhances performance of weaned piglets. In: P.D. Cranwell (editor), Manipulating Pig Production VII. Australasian Pig Science Association, Werribee, Victoria, p. 129. Varley, M.A., 1992. Neonatal survival: an overview. In: Proceedings of the British Society of Animal Science, Occasional Publication No. 15, pp. 1-7. Williams, I.H., 1976. Nutrition of the young sow in relation to body composition. PhD thesis, The University of Melbourne. Williams, I.H., 1995. Sow milk as a major nutrient source before weaning. In: D.P. Hennessy and P.D. Cranwell (editors), Manipulating Pig Production V. Australasian Pig Science Association, Werribee, Victoria, pp. 107-113.


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4

Behavioural changes and adaptations associated with weaning P. Mormède and M. Hay

Summary In modern husbandry, weaning is an abrupt transition between two extremely different conditions and imposes numerous challenges to piglets: nutritional (from milk diet to solid food), environmental (temperature, characteristics of the lodging system), social (separation from the dam, interactions with unknown mates), and physical (transportation). Therefore, weaning leads to intense taxation of adaptive processes, both at the behavioural and at the neuroendocrine level. The consequences of weaning are more intense with earlier ages, although detailed biological data are still scarce. Several behavioural and biological indices indicate that the welfare of the piglets may be compromised during this period of intense adaptation. Experimental data clearly show that the anorexia or, at least, the nutritional deficit due to the abrupt transition from milk to solid food plays a major role in these alterations. New experimental approaches have been developed, allowing a detailed investigation of neuroendocrine changes in urinary excretion of stress hormones (cortisol and catecholamines), together with the monitoring of behavioural changes and production traits. Those new approaches should allow more comprehensive studies of the different factors impinging upon piglets at weaning when nutritional needs are covered, as well as a better appraisal of the influence of age at weaning. This knowledge is necessary to adjust weaning procedures to ensure an optimal production rate without compromising the welfare of the animals.

4.1

Introduction

In natural or seminatural conditions, weaning in the pig is a progressive process taking place around 12 to 17 weeks (Jensen, 1986; Newberry and Wood-Gush, 1988; Stolba and Wood-Gush, 1989; Boe, 1991). In modern husbandry, piglets are usually weaned abruptly at the age of 3-4 weeks. It can occur even earlier with the practice of segregated early weaning, which allows a better control of some diseases, and with the use of hyperprolific sows, which leads to an excessive number of piglets to be raised by the sows (Worobec and Duncan, 1997). Weaning is a period of important and numerous changes for the young piglets, including: separation from the dam, reallocation involving mixing with strangers, introduction in a novel environment and eventually transportation to a distant place in the case of segregated weaning, the radical change from a milk diet to solid food, and various other changes in the physical environment (e.g. ambient temperature, nature of the floor, air quality). Therefore, weaning leads to intense taxation of adaptive processes, both


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at the level of behavioural adjustments and neuroendocrine and other biological systems (Dantzer and Mormède, 1983).

4.2

Neuroendocrine consequences of weaning

Most available neuroendocrine data concern the variation of cortisol in plasma. Cortisol is a secretion product of the adrenal gland released under stimulation by the anterior pituitary hormone ACTH that, itself, is under hypothalamic control (Mormède, 1995). Circulating cortisol levels are very high at delivery, and decrease sharply immediately after birth and then more slowly during the first weeks of life, to increase thereafter (Kattesh et al., 1990; Carroll et al., 1998). Adrenal reactivity to ACTH also decreases during the first post natal weeks (Kanitz et al., 1999). A transient increase of cortisol levels at weaning has been described in a number of studies, whatever the age of the piglets, although the change tends to be higher when the animals are weaned at a younger age (Worsaae and Schmidt, 1980; Dantzer and Mormède, 1981; Rantzer et al., 1995, 1997; Carroll et al., 1998). Glucocorticoid receptor levels in the hippocampus were also reduced after weaning, alike after snaring stress in adults (Kanitz et al., 1998). Although the changes of cortisol level are widely used as an index of stress, they are not stimulus-specific. It is thus difficult to dissociate the respective contribution of the various changes associated with weaning in the activation of the hypothalamic-pituitary-adrenal (HPA) axis. A number of single factors like fasting (Farmer et al., 1992), maternal deprivation (Klemcke and Pond, 1991), exposure to novel environments (Mormède and Dantzer, 1978; Désautés et al., 1999), simulated or real transportation (Mormède and Dantzer, 1978; Lamboij and Van Putten, 1993, Perremans et al., 2001), and mixing of animals (Bradshaw et al., 1996) can all activate the HPA axis and may therefore play a role in the increase of cortisol levels measured at weaning.

4.3

The critical role of food

One critical change associated with weaning is the shift from sow’s milk to a dry feed, which induces a period of fasting during the first few days following weaning. This weaning anorexia has a negative impact on growth and leads to mobilisation of fat stores, as shown by the sharp increase of circulating free fatty acid levels (Bark et al., 1996). It may also be involved in the digestive problems that are frequently encountered after weaning (McCracken et al., 1999). Experimental data indicate that this period of under-nutrition markedly alters the functioning of several neuroendocrine systems during the post-weaning period. For instance, the changes measured in the somatotrophic axis (increased GH and reduced IGF levels) and in the autonomic nervous system (reduced catecholamine excretion in urine) are similar to those measured in fasting animals (Carroll et al., 1998; Hay et al., 2001). These changes may be long lasting, as in the case of weaning at 6 days of age for instance (Hay et al., 2001) (figure 4.1). Some of the metabolic responses

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Behavioural changes and adaptations associated with weaning

b

10

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Figure 4.1. Consequences of early weaning (EW) on post-natal day 6 (C = control piglets raised by their dam). EW induced an early and persistent reduction in growth rate, that did not reach control values until the fourth post-natal week (panel a). EW transiently increased cortisol excretion in urine (panel c). EW induced an early and profound reduction in urinary levels of noradrenaline (panel b), that may be a consequence of starvation, in order to save calories via a reduction of heat production. This interpretation is supported by the change in thermoregulatory behavior of EW piglets that spend more time under the infrared lamp (panel e shows the proportion of piglets located under the infrared lamp, as recorded by scan sampling for 4 h/day). The reduction of adrenaline excretion in urine was postponed by a few days after EW, but was longlasting, as compared to noradrenaline (d), since adrenaline has a major role in the mobilisation of energy stores. The differential influence of EW on adrenaline and noradrenaline excretion is better illustrated by the ratio of the urinary content in both catecholamines (panel f). From Hay et al. (2001), with permission of Elsevier Science.


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to weaning can be corrected by milk feeding, which improves the growth rate of the animals as compared to dry feed (McCracken et al., 1995; Kim et al., 2001). Indeed, piglets weaned at 2-3 days of age and subsequently fed with a milk replacer display greater growth rates by day 7-8 of lactation than piglets raised by their dam, showing that sow milk yield is a limiting factor to piglet growth (Harrell et al., 1993). The increase of voluntary food intake after weaning by using whole cow’s milk also improves the mucosal architecture of the small intestine (Pluske et al., 1996). However, in commercial settings, weanling piglets are usually offered dry food, for economical reasons. Such a food is not accepted as well as a liquid milk replacer, and weaning alters average daily feed intake and average daily weight gain, the magnitude of which is larger with earlier weaning ages. As an example, Leibbrandt and collaborators showed that increasing weaning age (2, 3 and 4 weeks) resulted in reduced weight gain depression. All the animals nevertheless reached the same body weight at 6 weeks of age (Leibbrandt et al., 1975). Consumption of solid food by suckling piglets increases slowly and becomes significant only during the fourth week of age. Moreover, large differences among animals have been reported, and many piglets show no evidence of eating creep feed at the weaning age of 4 weeks (Barnett et al., 1989; Pajor et al., 1991; Fraser et al., 1994; Bruininx et al., 2002a). For instance, Bruininx and collaborators (2001) observed in 4-week piglets that the mean time to initiate feeding after weaning was 15.4 hours, with very large variation among individual piglets, ranging from a very short time up to four days after weaning. The initial feed intake was only slightly affected by sex or initial body weight, but occured sooner in animals eating significant amount of creep feed before weaning. Additionally, the daily weight gain was improved in those animals during the first weeks after weaning as compared to their littermates (Bruininx et al., 2002a). Much effort has been devoted to the development of highly palatable and easily digestible diet for nursing and weanling piglets, with mixed success. For instance, in an experiment with piglets weaned at 14-18 days of age, Gardner and collaborators (2001) compared the efficiency of two diets (a low-quality diet with a relatively high content of soybean meal and a high-quality diet enriched with blood plasma and fish meal) with and without addition of milk products. The low quality - no milk diet was slightly less consumed, but only during the first week after weaning, and the difference between diets disappeared thereafter. In accordance with the latter experiment, Lawlor et al. (2002) did not find any significant difference of feeding postweaning diets as dry pelleted feed, fresh liquid feed, acidified liquid feed and fermented liquid feed on pig performance from weaning (26 days) to harvest. Another attempt to increase food intake was made by increasing day length to 23 h (instead of 8 h). Although this lighting regimen was efficient to increase

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food intake and weight gain during the second week after weaning, no change could be observed during the first week (Bruininx et al., 2002b).

4.4

Behaviour

The behaviour of early weaned (6-day) piglets, as compared to animals raised by the dam, is characterised by an increase of vocalisations emitted during the first few days after weaning, increased restlessness, more aggressive behaviours and bellynosing, increased litter cohesion and increased time spent under the heating lamp (Orgeur et al., 2001). Most of these changes are still visible on day 20, i.e. 2 weeks after weaning, like some of the neuroendocrine changes (Hay et al., 2001). They have also been observed at various intensities in piglets weaned at older ages. For instance, belly-nosing, which consists of reciprocal massages, butting and sucking bouts, has been repeatedly described in weaned piglets, and its frequency increases when the age at weaning decreases (Boe, 1993; Worobec et al., 1999). Belly-nosing has been suggested to be a form of massaging that piglets would normally direct toward the udder both before and after a bout of suckling (Worobec and Duncan, 1997). However, the fact that it develops progressively over days after weaning and remains stable thereafter suggests that it may have its own psychobiological mechanisms and several authors have suggested that it reflects reduced welfare. As with belly-nosing, the increase of aggressive behaviours after weaning was found to be more intense when weaning occurred at a younger age (Worsaae and Schmidt, 1980; Orgeur et al., 2001). Aggressive behaviours are normal components of the behaviour of weaned pigs, but their high level of expression after early weaning may be part of the same general psychobiological syndrome indicative of altered welfare, together with belly-nosing and other behavioural changes.

4.5

Conclusion

There is no doubt that weaning is a period of intense stress for piglets, with profound consequences on growth, physiology, and disease outbursts, which reveal severe welfare problems. Experimental data clearly show that the anorexia or, at least, the nutritional deficit due to the abrupt transition between milk and solid food, induces severe taxation of the adaptive mechanisms of piglets and may be of special relevance from a welfare point of view. Most of the problem comes from the fact that during lactation spontaneous intake of dry food remains very low up to 3 weeks of age and does not become significant until the 4th week, indicating that the appetite for dry food is very low in younger piglets. The large individual variation suggests that this trait may be influenced by genetic factors and could therefore respond to genetic selection. It would be valuable to gain more information on the physiological changes induced by weaning at different ages. Indeed, most studies have focused solely on growth performance and behaviour up to now. Recent experiments showed however that measures of physiological stress, like urinary levels of catecholamines


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provide sensitive indications on the adaptation processes occurring at weaning and on the nature of the constraints imposed to piglets (Hay et al., 2001). Additionally, it would be interesting to design experiments where nutritional needs are covered, in order to assess the respective contribution of the other components involved in the stress of weaning (e.g. separation from the dam, transportation to remote places, change of the environment, mixing with unknown congeners).

References Bark, L.J., T.D. Crenshaw and V.D. Leibbrandt, 1986. The effect of meal intervals and weaning on free intake of early weaned pigs. Journal of Animal Science 62, 1233-1239. Barnett, K.L., E.T. Kornegay, C.R. Risley, M.D. Lindemann and G.G. Schurig, 1989. Characterization of creep feed consumption and its subsequent effects on immune response, scouring index and performance of weanling pigs. Journal of Animal Science 67, 2698-2708. Boe, K. 1991, The process of weaning in pigs: when the sow decides. Applied Animal Behavioural Science 30, 47-59. Boe, K. 1993. The effect of age at weaning and post-weaning environment on the behaviour of pigs. Acta Agriculturae Scandanavica 43, 173-180. Bradshaw, R.H., R.F. Parrott, J.A. Goode, D.M .Lloyd, R.G. Rodway and D.M. Broom, 1996. Behavioural and hormonal responses of pigs during transport: effect of mixing and duration of the journey. Animal Science 62, 547-554. Bruininx, E.M.A.M., C.M.C. Peet-Schwering, J.W. Schrama, P.F.G. Vereijken, P.C. Vesseur, H. Everts, L.A. Den Hartog and Beynen, A.C., 2001. Individually measured feed intake characteristics and growth performance of group-housed weanling pigs: effects of sex, initial body weight, and body weight distribution within groups. Journal of Animal Science 79, 301-308. Bruininx, E.M.A.M., G.P. Binnendijk, C.M.C. Peet-Schwering, J.W. Schrama, L.A. Den Hartog, H. Everts and A.C. Beynen, 2002a. Effect of creep feed consumption on individual feed intake characteristics and performance of group-housed weanling pigs. Journal of Animal Science 80, 1413-1418. Bruininx, E.M.A.M., M. J. W. Heetkamp, D. van der Bogaart, C. M. C. Peet-Schwering, A.C. Beynen, H. Everts, L. A. Den Hartog and J.W Schrama, 2002b. A prolonged photoperiod improves feed intake and energy metabolism of weanling pigs. Journal of Animal Science 80, 1736-1745. Carroll, J.A., T.L. Veum and R.L. Matteri, 1998. Endocrine responses to weaning and changes in post-weaning diet in the young pig. Domestic Animal Endocrinology 15, 183-198. Dantzer, R. and P. Mormède, 1981. Influence du mode d’élevage sur le comportement et l’activité hypophyso-corticosurrénalienne du porcelet. Reproduction, Nutrition, Development 21, 661670. Dantzer, R. and P. Mormède, 1983. Stress in farm animals: a need for reevaluation. Journal of Animal Science 57, 6-18. Désautés, C., A. Sarrieau, J.C. Caritez and P Mormède, 1999. Behaviour and pituitary-adrenal function in Large White and Meishan pigs. Domestic Animal Endocrinology 16, 193-205.

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Farmer, C., D. Petitclerc, G. Pelletier, P. Gaudreau and P. Brazeau, 1992. Carcass composition and resistance to fasting in neonatal piglets born of sows immunized against somatostatin and/or receiving growth hormone-releasing factor injections during gestation. Biology of the Neonate 61, 110-117. Fraser, D., J.J.R. Feddes, and E.A. Pajor, 1994. The relationship between creep feeding behavior of piglets and adaptation to weaning: effect of diet quality. Canadian Journal of Animal Science 74, 1-6. Gardner, J.M., C.F.M. de Lange and T.M. Widowski, 2001. Belly-nosing in early-weaned piglets is not influenced by diet quality or the presence of milk in the diet. Journal of Animal Science 79, 73-80. Harrell, R. J., M. J. Thomas and R. D Boyd, 1993. Limitations of sow milk yield on baby pig growth. Proc. Cornell Nutr. Conf., Ithaca, NY, 156-164. Hay, M., P. Orgeur, F. Lévy, J. Le Dividich, D. Condorcet, R. Nowak, B. Schaal and P. Mormède, 2001. Neuroendocrine consequences of very early weaning in swine. Physiology and Behaviour 72, 263-269. Jensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Applied Animal Behavioural Science 16, 131-142. Kanitz, E., G. Manteuffel and W. Otten, 1998. Effects of weaning and restraint stress on glucocorticoid receptor binding capacity in limbic areas of domestic pigs. Brain Research 804, 311-315. Kanitz, E., W. Otten, G. Nürnberg and K.P. Brüssow, 1999. Effects of age and maternal reactivity on the stress response of the pituitary-adrenocortical axis and the sympathetic nervous system in neonatal pigs. Animal Science 68, 519-526. Kattesh, H.G., S.F. Charles, G.A. Baumbach and B.E. Gillespie, 1990. Plasma cortisol distribution in the pig from birth to six weeks of age. Biology of the Neonate 58, 220-226. Kim, J.H., K.N. Heo, J. Odle, I.K. Han and R.J Harrell, 2001. Liquid diets accelerate the growth of early-weaned pigs and the effects are maintained to market weight. Journal of Animal Science 79, 427-434. Klemcke, H.G. and W.G. Pond, 1991. Porcine adrenal adrenocorticotropic hormone receptors; characterization, changes during neonatal development, and response to a stressor. Endocrinology 128, 2476-2488. Lambooij, E. and G. Van Putten, 1993. Transport of pigs. In: T. Grandin (editor), Livestock Handling and Transport. CAB International, Wallingford, UK, pp. 213-231. Lawlor, P.G., P.P. Lynch, G.E. Gardiner, P.J. Caffrey and J.V. O’Doherty, 2002. Effect of liquid feeding weaning pigs on growth performance to harvest. Journal of Animal Science 80, 1725-1735. Leibbrandt, V.D., R.C. Ewan, V.C. Speer and D.R. Zimmerman, 1975. Effect of weaning and age at weaning on baby pigs performance. Journal of Animal Science 40, 1077-1080. McCracken, B.A., H.R. Gaskins, P.J. Ruwe-Kaiser, K.C. Klasing and D.E. Jewell, 1995. Dietdependent and diet independent metabolic responses underlie growth stasis of pigs at weaning. Journal of Nutrition 125, 2838-2845. McCracken, B.A., M.E. Spurlock, M.A. Roos, F.A. Zuckermann and H. R. Gaskins, 1999. Weaning anorexia may contribute to local inflammation in the piglet small intestine. Journal of Nutrition 129, 613-619.


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Mormède, P. 1995. Le stress : interaction animal-homme-environnement, Cahiers Agricultures 4, 275-286. Mormède, P. and R. Dantzer, 1978. Behavioural and pituitary-adrenal characteristics of pigs differing by their susceptibility to the malignant hyperthermia syndrome induced by halothane anesthesia. 2 - Pituitary-adrenal function. Annales Recherches Veterinaires 9, 569-576. Newberry, R C. and D.G.M. Wood-Gush, 1988. Development of some behaviour pattern in piglets under semi-natural conditions. Animal Production 46, 103-109. Orgeur, P., M. Hay, P. Mormède, H. Salmon, J. Le Dividich, R. Nowak, B. Schaal and F Lévy, 2001. Behavioural, growth and immune consequences of early weaning in one-week-old Large White piglets. Reproduction, Nutrition, Development 41, 321-332. Pajor, E.A., D. Fraser and D.L. Kramer, 1991. Consumption of solid food by suckling pigs: individual variation and relation to weight gain. Applied Animal Behavioural Science 32, 139-155. Perremans, S., J.M. Randall, G. Rombouts, E. Decuypere and R. Geers, 2001. Effect of whole-body vibration in the vertical axis on cortisol and adrenocorticotropic hormone levels in piglets. Journal of Animal Science 79, 975-981. Pluske, J. R., I.H. Williams and F.X. Aherne, 1996. Villous height and crypt depth in piglets in response to increases in the intake of cow’s milk after weaning. Animal Science 62, 145-158. Rantzer, D., J. Svendsen and B. Weström, 1995. Weaning of pigs raised in sow-controlled and in conventional housing systems. 2. Behaviour studies and cortisol levels. Swedish Journal of Agricultural Research 25, 61-71. Rantzer, D., J. Svendsen and B. Weström, 1997. Weaning of pigs in group housing and in conventional housing systems for lactating sows. Swedish Journal of Agricultural Research 27, 23-31. Stolba, A. and D.G.M. Wood-Gush, 1989. The behaviour of pigs in a semi-natural environment. Animal Production 48, 419-425. Worobec, E. and I.J.H. Duncan, 1997. Early weaning in swine: a behavioural review. Compendium of Continueng Education for the Practising Veterinariun 9, S271-S277. Worobec, E., I.J.H. Duncan and T.M. Widowski, 1999. The effect of weaning at 7,14 and 28 days on piglet behaviour. Applied Animal Behavioural Science 62, 173-182. Worsaae, H. and M. Schmidt, 1980. Plasma cortisol and behaviour in early weaned piglets, Acta Veterinaria Scandanavica 21, 640-657.

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5

Metabolic and endocrine changes around weaning F.R. Dunshea

5.1

Introduction

One of the major stressors for the weaning pig is the rapid change from a liquid milk based diet to a solid pelleted cereal-based diet. All this occurs at the same time as the pigs are introduced into a new environment, mixed with other pigs and removed from the sow. The combined effect of this transition and these stressors is that newly weaned pigs often lose considerable weight (up to 10% of live weight) over the first 2 days post-weaning and may not regain this weight for up to 7 days post-weaning. These effects are more pronounced in young and small-for-age pigs (Power et al. 1996). The metabolic and endocrine changes that occur at this time are equally profound. In this chapter I will discuss the metabolic and endocrine events that occur after weaning and some of the interventions that have been tried to reduce this growth check.

5.2

The post-weaning check

Between birth and weaning, sucking pigs grow at approximately 220 g/day (King et al. 1993), but this growth rate is far below the biological potential of the artificiallyreared pig (Hodge, 1974). For example, pigs weaned at 2-3 days of age and fed cow’s milk or milk replacer alone until 21 days of age, can achieve growth rates in excess of 400 g/day (Harrell et al. 1993; Dunshea et al. 2002a). Since the sow increases milk production over the first two weeks of lactation before reaching a plateau (Toner et al. 1995), the extent to which milk yield limits piglet growth rate is exacerbated as lactation advances. For example, from d 21 of lactation, suckling piglet growth rate decreases, particularly in large litters (Cranwell et al. 1995a; Dunshea and Walton, 1995). That milk yield constrains piglet growth was demonstrated by Cranwell et al. (1995). Except for the period immediately after weaning (27-35 days) pigs exhibited considerably faster growth rate in all postweaning periods than they did while on the sow. To accommodate this decline in nutrient supply, suckling piglets may commence to eat creep feed, or sows feed, from about three weeks of age. However, the intakes of dry creep feeds are generally low and unlikely to significantly increase pre-weaning growth rate of pigs (Pluske et al. 1995). Also, given that in many parts of the world weaning typically occurs now at 21 d or younger, most piglets have had little opportunity to consume solid feed. It is little wonder then, that newly-weaned piglets consume very little feed over the first few days post weaning. The post-weaning check in body weight occurs in pigs that are heavy- or light-for-age (Figure 5.1; Dunshea et al. 2000a, 2002a,b)


61

Change from weaning weight (g)

Dunshea

a

6000 5000 4000 3000 2000 1000 0 -1000

Change from weaning weight (g)

0

2

4

6 8 10 Days post-weaning

12

14

16

12

14

16

b

6000 5000 4000 3000 2000 1000 0 -1000 0

2

4

6

8

10

Days post-weaning

Figure 5.1. Effect of sex, weaning age and weaning weight on growth in pigs weaned onto solid diets. Animals were either weaned at between 12 and 17 days (Figure 5.1a) or 20 and 28 days (Figure 5.1b). Boars are depicted as open symbols and gilts as closed symbols. Light-, average- and heavy-for age pigs are depicted as triangles, squares or circles, respectively. Data are collated from a number of studies conducted by the author (Power et al. 1996; Dunshea, 2001; Dunshea et al 1.999a;2000a,b;2002b,c).

and is greater and lasts longer in early-weaned pigs (Power et al. 1996; Dunshea et al. 2002b). Collation of data from a number of studies conducted by the author demonstrate that pigs weaned at greater than 20 days of age take approximately 4 days to return to weaning weight, whereas pigs weaned at less than 17 days of age may not return to weaning weight until after 7 days post-weaning (Figure 5.1). The post-weaning check is also greater in boars and barrows than in gilt piglets (Power et al. 1996; Dunshea et al. 1999a; Dunshea, 2001; Bruininx et al. 2002) although this difference is only transient in nature. The reason for the reduction in live weight is the failure of weaned pigs to consume dry feed. Le Dividich and Seve (2000) collated data from 7 studies on feed intake

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Metabolic and endocrine changes around weaning

immediately before and after weaning. Average milk energy intake prior to weaning was approximately 1250 kJ/kg0.75/day. On the day after weaning, solid feed intake was approximately 25% that achieved before weaning. By 1 week postweaning solid feed intake had increased but was still only 60-70% of that consumed prior to weaning. In a very comprehensive study, Bruininx et al. (2001) investigated the effect of weaning weight on time taken to first consume feed and found that on average it took approximately 15 h until pigs first consumed dry food. However, over half (53%) of the pigs had consumed food in the first 4 h after weaning when the lights were turned off for 12 h. Over the next 12 h of darkness only a further 3% of pigs commenced feeding. During the following 12 of light a further 32% of the pigs commenced feeding. These data suggest that although it can take some considerable time before weaned pigs consume feed there may be some potential to influence this by changing light patterns (Bruininx et al. 2002). The low feed intake and growth check immediately after weaning are consistent with a large number of observations in our laboratory (Power et al. 1996; Dunshea, 2001; Dunshea et al. 1999a,b; 2000a, b;2002a,b,c). The low feed intake, and poor or even negative growth rates, can be largely overcome by feeding the weaned pigs liquid instead of dry diets (Lecce et al. 1979; Odle and Harrell, 1998). Liquid diets (skim milk) have also been used to supplement dry post-weaning diets with considerable success especially if the pigs received the same liquid diet as a supplement prior to weaning (Dunshea et al. 1999a). Growth rates and DM intakes of up to 240 g/day and 260 g/day respectively, in the 7 days after weaning, were recorded in pigs supplemented with a liquid diet before and after weaning compared with growth rates of 0.05)

6.10

Liquid feeding post-weaning

The case for liquid feeding young pigs has been reviewed recently (Brooks et al., 2001) so only a brief summary is included here, focussing on the behavioural aspects of this method of feeding.

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Factors affecting the voluntary feed intake of the weaned pig

In view of the problems that the piglet has in discriminating hunger and thirst it might be anticipated that post-weaning performance would be improved by offering a liquid diet. Liquid feeding has potential advantages because: -

• It provides a diet with a dry matter concentration more like that of sow milk and more like the solid food that the pig would encounter in the wild. This might encourage intake and maintain continuity of nutrient supply. • It provides a diet that more closely meets the piglet’s need for both nutrients and water. • It overcomes some of the problems posed by the piglets having to learn to satisfy their drives of hunger and thirst separately. Until relatively recently, liquid feeding was confined to the use of milk replacer for the artificial rearing of pigs or for pigs weaned at very young ages. In this context, and with good hygiene, it has been demonstrated that pigs will grow faster on liquid diets than they will on the sow (Odle and Harrell, 1998) Liquid feeding has been limited in application because of the problems in maintaining the feed in a wholesome and palatable form. However, developments in delivery systems had resulted in renewed interest in the approach. If feed hygiene can be maintained, feed intake and growth of weaners is increased by feeding liquid diets and further improved by feeding fermented liquid diets (Table 6.11). The greatest benefits were obtained in the week immediately following weaning where dry matter intake and growth rate are improved by 20-30% (Kim et al., 2001; Russell et al., 1996). Importantly, the acceleration of early growth is maintained to market weight (Kim et al., 2001). Pig producers have been encouraged to offer pigs a liquid ‘porridge’ or ‘gruel’ in addition to dry feed in the immediate post weaning period. Experimental data on this is sparse and contradictory. In one study (Beattie et al., 1999), feed intake in

Table 6.11. Improvement (%) in growth rate and food conversion ratio in experiments in which the performance of pigs fed dry feed (DF), liquid feed (LF) or fermented liquid feed (FLF) was compared (From the review of Jensen and Mikkelsen, 1998). No. of trials

LF v. DF 10 FLF v. DF 4 FLF v. LF 3

Improved daily weight gain

Improved food conversion ratio

Mean ± SD

Range

Mean ± SD

Range

12.3 ± 9.4 22.3 ± 13.2 13.4 ± 7.1

-7.5 - 34.2 9.2 - 43.8 5.7 - 22.9

-4.1 ± 11.8 -10.9 ± 19.7 -1.4 ± 2.4

-32.6 - 10.1 -44.3 - 5.8 -4.8 - 0.6


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Brooks and Tsourgiannis

the 2 days following weaning was improved by offering additional wet feed in an easily accessible trough increased, but growth performance was not improved over the 3 week post-weaning period. In another study, Dunshea et al. (2000) provided weaned pigs with supplemental fermented milk for 8 days after weaning and reported significantly increased growth rates and pigs that were 20% heavier at 42 days of age. In our own studies, the growth rate of pigs offered fermented liquid feed in addition to dry feed was intermediate between that of pigs offered either a dry or a liquid diets (Brooks et al., 2001). An important observation in this study was that, compared with the pigs offered liquid or dry diets, more of the pigs offered a choice of diets engaged in antisocial behaviours such as belly-nosing. Given the previous discussion it is clear that it may not be a sensible approach to offer both dry and liquid diets. The weaned pig already has the challenge of learning to differentiate between hunger and thirst and recognising that food and water will satisfy these needs. Providing it with water, food and a third option of wet feed is likely to hamper this learning process not accelerate it.

6.11

Conclusions

From the discussion above, it is clear that a wide range of different factors affect the behaviour of the newly weaned pig and many of these impact directly or indirectly on its ability to find feed and water (see summary Table 6.12). In addition, either through lack of experience, or because its homeostatic control mechanisms have not matured, the piglet can fail to satisfy its physiological requirements for water and/or nutrients. Thus, the theoretical models of voluntary food intake that we would employ to describe the control of intake of food and water in pigs with mature homeostatic mechanisms have no value when trying to explain the phenomena observed in the period immediately post-weaning when pigs are weaning at 5 weeks of age or less. Our attempts to improve performance of the newly weaned pig need to focus on the development of management strategies that will increase the independence of the weaned pig from its dam and increase its exploratory behaviour. In this context we may need to concentrate on the effects that pre-weaning environment can have on equipping the pig to cope with the changes it faces at weaning. Recent reports have shown that the housing experienced by sows may affect the behaviour of their piglets (Beattie et al., 1996), that enriched environments increase piglet activity (Beattie et al., 1994), and that piglets from outdoor farrowing systems feed more frequently than pigs from confinement systems (Cox and Cooper, 2001; Webster and Dawkins, 2000). These findings may point the way forward, suggesting as they do that more diverse and stimulating environments encourage the development of exploratory skills that may assist the piglet in making the transition to independence.

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Table 6.12. Summary of factors affecting feed and water intake in weaned pigs (2128 days of age). Factors adversely affecting feed intake in the newly-weaned pig

Factors adversely affecting water intake in the newly-weaned pig

Lack of previous experience of eating solid food and/or drinking. (Underdeveloped feeding, drinking and exploratory behaviour). Inability to discriminate between hunger and thirst. Inability to find food or water (unfamiliar feed and water presentation). Cold conditions (pigs huddle rather than actively seeking food or water). Hot conditions (pigs rest rather than actively seeking food or water). Agonistic behaviour (fighting in mixed pigs displaces other behaviours). Lack of feeding stimulus . (no sow vocalisations)

Water quality (flavour, mineral content, microbiology).

Palatability (taste, smell, texture, freshness, nutrient balance).

Water temperature (cold water reduces intake in cold conditions, hot water reduces intake in hot conditions).

Feed availability (accessibility of feeding places).

Water availability (accessibility of drinkers, flow rate).

Inadequate or excessive water intake

What is not clear from the literature is whether we should be encouraging the weaned pig to develop individual foraging behaviour, or reinforcing synchronous group feeding as a way of ensuring that all piglets in a cohort make a successful transition to solid food. The answer to this question may differ according to the weaning age and hence the ease with which modifications can be made to entrained behaviour. This fundamental question needs answering. Without a satisfactory answer, it is not possible to specify feeding and watering equipment or to devise management systems that will optimise the performance of all the individuals within a group.

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Horrell, I., 1997. The characterisation of suckling in wild boar. Applied Animal Behavioural Science 53, 271-277. Jensen, B.B. and L.L. Mikkelsen, 1998. Feeding liquid diets to pigs. In: P.C. Garnsworthy and J. Wiseman, (eds). Recent Advances in Animal Nutrition 1998. pp. 107-126. Nottingham University Press, Thrumpton, Nottingham. Jensen, P., 1986. Observations on the maternal-behavior of free-ranging domestic pigs. Applied Animal Behavioural Science 16, 131-142. Jensen, P., 1995. The weaning process of free-ranging domestic pigs: Within- and between-litter variations. Ethology 100, 14-25. Jensen, P. and I. Redbo, 1987. Behavior during nest leaving in free-ranging domestic pigs. Applied Animal Behavioural Science 18, 355-362. Jensen, P. and B. Recen, 1989. When to wean - observations from free-ranging domestic pigs. Applied Animal Behavioural Science 23, 49-60. Jensen, P., J. Rushen and B. Forkman, 1995a. Behavioral strategies or just individual variation in behavior - a lack of evidence for active and passive piglets. Applied Animal Behavioural Science 43, 135-139. Jensen, P., B. Forkman, K. Thodberg and E. Koster, 1995b. Individual variation and consistency in piglet behavior. Applied Animal Behavioural Science 45, 43-52. Kabuga, J.D. and S.Y. Annor, 1992. A note on the development of behaviour of intensively managed piglets in the humid tropics. Animal Production 54, 157-159. Kasanen, S. and B. Algers, 2002. A note on the effects of additional sow gruntings on suckling behaviour in piglets. Applied Animal Behavioural Science 75, 93-101. Kavanagh, S., P.B. Lynch, P.J. Caffrey and W.D. Henry, 1995. Creep-feed intake by suckling pigs. Irish Journal of Agricultural and Food Research 34, 87 (Abstr.). Keeling, L.J. and J.F. Hurnik, 1996. Social facilitiation and synchronization of eating between familiar and unfamiliar newly weaned piglets. Acta Agriculturae Scandinavica 46, 54-60. Kelly, D. and T.P. King, 2001. Luminal bacteria: Regulation of gut function and immunity. In: A. Piva, K.E. Bach Knudsen and J.E. Lindberg, (eds). Gut environment of the pig. pp. 113-131. Nottingham University Press, Nottingham. Kidder, D.E. and M.J. Manners, 1978. Digestion in the pig. Scientechnia, Bristol. Kim, J.H., K.N. Heo, J. Odle, I.K. Han and R.J. Harrell, 2001. Liquid diets accelerate the growth of early-weaned pigs and the effects are maintained to market weight. Journal of Animal Science 79, 427-434. Lewis, N.J. and J.F. Hurnik, 1985. The development of nursing behaviour in swine. Applied Animal Behavioural Science 14, 225-232. Lewis, N.J. and J.F. Hurnik, 1986. An approach response of piglets to the sows nursing vocalisations. Canadian Journal of Animal Science 66, 537-539. Mackenzie, D.D.S. and D.K. Revell, 1998. Genetic influences on milk quality. In: M. Verstegen, J. Schrama and P. Moughan, (eds). The Lactating Sow. pp. 97-112. Wageningen Pers, Wageningen. Maenz, D.D., J.F. Patience and M.S. Wolynetz, 1993. Effect of water sweetener on the performance of newly weaned pigs offered medicated and unmedicated feed. Canadian Journal of Animal Science 73, 669-672.


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McBride, G., 1963. The ‘teat order’ and communication in young pigs. Animal Behaviour 11, 5356. McLeese, J.M., M.L. Tremblay, J.F. Patience and G.I. Christison, 1992. Water-intake patterns in the weanling pig - effect of water-quality, antibiotics and probiotics. Animal Production 54, 135142. Mennella, J.A. and G.K. Beauchamp, 1991. Maternal diet alters the sensory qualities of humanmilk and the nurslings behavior. Pediatrics 88, 737-744. Mennella, J.A. and G.K. Beauchamp, 1993. The effects of repeated exposure to garlic-flavored milk on the nurslings behavior. Pediatric Research 34, 805-808. Mennella, J.A., C.P. Jagnow and G.K. Beauchamp, 2001. Prenatal and postnatal flavor learning by human infants. Pediatrics 107, U11-U16. Metz, J.H.M. and H.W. Gonyou, 1990. Effect of age and housing conditions on the behavioural and haemolytic reaction piglets to weaning. Applied Animal Behavioural Science 27, 299-309. Morgan, C.A., A.B. Lawrence, J. Chirnside and L.A. Deans, 2001. Can information about solid food be transmitted from one piglet to another? Animal Science 73, 471-478. Nabuurs, M.J.A., A. Hoogendoorn and A. VanZijderveldVanBemmel, 1996. Effect of supplementary feeding during the sucking period on net absorption from the small intestine of weaned pigs. Research in Veterinary Science 61, 72-77. Nagai, M., K. Hachimura and K. Takahashi, 1994. Water-consumption in suckling pigs. Journal of Veterinary Medicine Science 56, 181-183. Newberry, R.C. and D.G.M. Wood-Gush, 1984. The suckling behaviour of domestic pigs in a seminatural environment. Behaviour 95, 11-25. Newberry, R.C. and D.G.M. Wood-Gush, 1985. The suckling behaviour of domestic pigs in a seminatural environment. Behaviour 95, 11-25. Nicol, C.J. and S.J. Pope, 1994. Social-learning in sibling pigs. Applied Animal Behavioural Science 40, 31-43. Nienaber, J.A. and G.L. Hahn, 1984. Effects of water-flow restriction and environmental-factors on performance of nursery-age pigs. Journal of Animal Science 59, 1423-1429. Odle, J. and R.J. Harrell, 1998. Nutritional approaches for improving neonatal piglet performance: Is there a place for liquid diets in commercial production? Review. Asian-Australasian Journal of Animal Science 11, 774-780. Ogunbameru, B.O., E.T. Kornegay and C.M. Wood, 1991. A comparison of drip and non-drip nipple waterers used by weanling pigs. Canadian Journal of Animal Science 71, 581-583. Pajor, E.A., D. Fraser and D.L. Kramer, 1991. Consumption of solid food by suckling pigs - individual variation and relation to weight-gain. Applied Animal Behavioural Science 32, 139-155. Petersen, V., 1994. The development of feeding and investigatory behavior in free- ranging domestic pigs during their first 18 weeks of life. Applied Animal Behavioural Science 42, 87-98. Petrie, C.L. and H.W. Gonyou, 1988. Effects of auditory, visual and chemical stimuli on the ingestive behavior of newly weaned piglets. Journal of Animal Science 66, 661-668. Phillips, P.A. and M.H. Phillips, 1999. Effect of dispenser on water intake of pigs at weaning. Transactions of the ASAE 42, 1471-1473. Pluske, J.R., I.H. Williams and F.X. Aherne, 1996a. Villous height and crypt depth in piglets in response to increases in the intake of cows’ milk after weaning. Animal Science 62, 145-158.

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Pluske, J.R., I.H. Williams and F.X. Aherne, 1996b. Maintenance of villous height and crypt depth in piglets by providing continuous nutrition after weaning. Animal Science 62, 131-144. Pluske, J.R., D.J. Hampson and I.H. Williams, 1997. Factors influencing the structure and function of the small intestine in the weaned pig: A review. Livestock Production Science 51, 215-236. Puppe, B. and A. Tuchscherer, 1999. Developmental and territorial aspects of suckling behaviour in the domestic pig (sus scrofa f. Domestica). Journal of Zoology 249, 307-313. Puppe, B., M. Tuchscherer, S. Hoy and A. Tuchscherer, 1993. Social-organization structures in intensively kept pigs .1. Ethological investigations on the sucking order. Archiv fur TierzuchtArchives of Animal Breeding 36, 539-550. Rudo, N.D., I.H. Rosenberg and R.W. Wissler, 1976. The effect of partial starvation and glucagon treatment on intestinal villus morphology and cell migration. Proceedings of the Society for Experimental Biology and Medicine 152, 277-280. Russell, P.J., T.M. Geary, P.H. Brooks and A. Campbell, 1996. Performance, water use and effluent output of weaner pigs fed ad libitum with either dry pellets or liquid feed and the role of microbial activity in the liquid feed. Journal of the Science of Food and Agriculture 72, 8-16. Sorensen, M.T., B.B. Jensen and H.D. Poulsen, 1994. Nitrate and pig manure in drinking-water to early weaned piglets and growing pigs. Livestock Production Science 39, 223-227. Spinka, M., G. Illmann, B. Algers and Z. Stetkova, 1997. The role of nursing frequency in milk production in domestic pigs. Journal of Animal Science 75, 197-212. Spitz, F., 1986. Current state of knowledge of wild boar biology. Pig News and Information 7, 171175. Standing Committee on Agriculture; Pig Subcommittee, 1987. Feeding standards for Australian livestock. Pigs. CSIRO, East Melbourne, Victoria, Australia. Steiner, M., H.R. Bourges, L.S. Freedman and S.J. Gray, 1968. Effect of starvation on the tissue composition of the small intestine in the rat. American Journal of Physiology 215, 75-77. Thorpe, J., B.G. Miller and H. Schulze, 1998. The effect of liquid feeding at different feed intervals on ileal digestibility in the early weaned pig. In: J.A.M. van Arendonk, V. Ducrocq, Y. van der Honing, F. Madec, T. van der Lende, D. Puller, J. Folch, E.W. Fernandez and E.W. Bruns, (eds). Book of Abstracts of the 49th meeting of the European Association of Animal Production. Warsaw, Poland. 24th-29th August. pp. 264 (abs). Wageningen Pers, Wageningen. Webster, S. and M. Dawkins, 2000. The post-weaning behaviour of indoor-bred and outdoor-bred pigs. Animal Science 71, 265-271. Wechsler, B. and N. Brodmann, 1996. The synchronisation of nursing bouts in group housed sows. Applied Animal Behavioural Science 47, 191-199. Whittemore, C.T. and D. Fraser, 1974. The nursing and suckling behaviour of pigs. Ii. Vocalisation of the sow in relation to suckling behaviour and milk ejection. British Veterinary Journal 130, 346-356. Yang, T.S., B. Howard and W.V. McFarlane, 1981. Effects of food on drinking behaviour of growing pigs. Applied Animal Ethology 7, 259-270. Yang, T.S., M.A. Price and F.X. Aherne, 1984. The effect of level of feeding on water turnover in growing pigs. Applied Animal Behavioural Science 12, 103-109. Zabielski, R., 1998. Regulatory peptides in milk, food and in the gastrointestinal lumen of young animals and children. Journal of Animal and Feed Sciences 7, 65-78.


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Zijlstra, R.T., K.Y. Whang, R.A. Easter and J. Odle, 1996. Effect of feeding a milk replacer to earlyweaned pigs on growth, body composition, and small intestinal morphology, compared with suckled littermates. Journal of Animal Science 74, 2948-2959.

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7

Digestive physiology of the weaned pig H.M. Miller and R.D. Slade

Summary Descriptions of the changes in piglet digestive physiology following weaning abound in the literature to such an extent that review of the subject is suited more to a dedicated book than just this one chapter. Accordingly we have attempted to draw the literature together into a brief yet cohesive analysis of intestinal events pre and post-weaning. In doing so we have encapsulated conventional opinion whilst endeavouring to introduce novel or poorly documented perspectives. We hope that this review will help to provoke thought and stimulate continuing innovative research in this fascinating area.

7.1

Introduction

Profound changes in piglet digestive physiology occur following weaning as the piglet gut adapts to the change in feed type. In wild pigs these changes would occur progressively over time as the piglet made a gradual transition from a wholly milk diet to a wholly non-milk diet, the piglets finally achieving nutritional independence from the sow at about 8 to 12 weeks of age. However in the commercial situation piglets are weaned suddenly and uncompromisingly by removal from the sow and her milk supply at 14 to 28 days of age. Although highly digestible diets are supplied to the newly weaned piglet, such weaning practice is invariably associated with a dramatic reduction in feed intake, which in turn is associated with rapid changes in gut structure and function and reduced overall growth rate. Whilst traditionally the effects of sudden early weaning have been compared with delayed weaning (35 to 42 days) or gradual weaning in the continuing presence of the sow, such a dramatic change in piglet diet is not without precedent. At birth the piglet must face a symphony of changes in which the successful switch from placental to enteral nutrition plays a key role. Although the gut has had the whole of gestation to develop a structure suitable for enteral nutrition, extensive functional changes have to occur within hours of birth to enable adequate digestion and absorption. This adaptation to enteral nutrition at birth is accomplished with an alacrity that is markedly absent in the commercial weaning situation. In this review we will discuss the changes in gut structure and function that occur with current commercial weaning practice. In addition to describing how these changes may be affected by age at weaning we have also compared them with the developmental strategies of the neonatal pig. We hope that this may help us to understand regulation of postweaning events and thereby improve our ability to counteract the characteristic post-weaning check in piglet growth. Where appropriate


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we have also made comparisons with digestive development in other species, however distinctive differences in gestational, post-natal and post-weaning development between the pig (precocial) and altrical species (eg. rat, mouse and rabbit) prohibit generalised comparisons of their digestive physiology. In addition, the pig has frequently been used as a model for human research because of the homogeneity of anatomy, physiology, nutrition and metabolism across the two species (Moughan et al., 1992; Wykes et al., 1993; Ball et al., 1995). Just as the pig is regarded as a good model for the human we likewise consider the human to be a good model for the pig and therefore, where research progress in human infant digestive physiology exceeds that made in the pig, a cautious paralleling of developmental aspects of the two species has been made.

7.2

Strategies for adaptation to enteral nutrition in the neonatal pig

The rapid changes in the structure and function of the digestive tract that are triggered by weaning undoubtedly result in a transient period of sub optimal digestive competence. Let us first consider how similar problems are resolved in the neonate. 7.2.1

Preparation

During gestation the complex multicellular systems required for postnatal nutrition develop progressively (Zabielski et al., 1999) so that by the time of birth the architecture and mechanisms required for extra-uterine life are already established. Differentiation of the gut into individual recognisable organs is complete early in gestation. Thereafter refinement of the structure and development of digestive and absorptive systems must take place. Fetal and neonatal gastric development in pigs are described in recent reviews by Sangild et al. (2000) and Xu et al. (2000). Prenatal growth of the stomach is similar to whole body growth. Gastric fluid pH (important for bacterial suppression and activation of gastric zymogens) gradually reduces during gestation to reach 2-4 at birth. These reductions are paralleled by increases in both intrinsic factor in the gastric fundus, and gastrin. Development of proteolytic capability coincides with birth and is evidenced initially by activity of milk clotting chymosins and, with increasing age, by the general proteolytic activity of pepsins. Immediately post-partum, growth of the stomach exceeds that of the whole body, its mass increasing approximately two-fold from birth to 7 days of age (doa). Gastric acid secretory capacity doubles during the 24 hours following birth (presumably secretagogue stimulated) and again between 1 and 3 doa. This reflects augmentation of the gastric tissue and increased gastric gland oxyntic cell volume density and

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Digestive physiology of the weaned pig

HCl secretory capacity per unit of tissue mass. Gastric proteolytic competence also develops rapidly after birth with protease secretory capacity enhanced 9-fold by 7 doa. Structural development and cytodifferentiation of the fetal intestinal mucosa follow a highly organised temporal pattern. Briefly, villi forming from the presumptive small intestine mucosa are separated one from another by distinct regions of proliferating cells termed primordial crypts. Subsequently, primordial crypt cells invade the underlying mesenchyme to form crypt cell regions. Cells produced in the crypt regions differentiate and mature as they migrate along the crypt to villus axis. Thus, villus form and function emerge during fetal development. For example, mechanisms for amino acid transport have been detected in porcine fetal villus enterocytes as early as 40% gestation (Buddington and Malo, 1996). Rate of amino acid absorption increases as gestation progresses and rapidly immediately prior to birth (Buddington et al., 2001), suggesting that the transport mechanisms continue to be upregulated as gestation proceeds. Similarly, capacities for carbohydrate digestion and absorption are already established at birth (Manners and Stevens, 1972; Puchal and Buddington, 1992). Following resolution of villus structure and enterocyte differentiation, ingestion of amniotic fluid is thought to contribute significantly toward gastro intestinal growth (Buddington, 1993; Buddington et al., 2001) and may have positive priming effects on post-partum enterocyte competence. Thus fundamental mucosal characteristics associated with enteral nutrition are fully developed prior to birth. Prenatal development of enzyme activities is not limited to intestinal tissues alone. Pancreatic enzyme activities increase as gestation progresses (Westrom et al., 1987) and appear to be maximal by the end of gestation, as demonstrated for elastase II (Gestin et al., 1997a) and chymotrypsin (Gestin et al., 1997b). There is little discussion of prenatal development of the porcine colon in the literature. The colon functions to absorb water and electrolytes, and this function appears developed in the neonate. Conservation of dietary carbohydrate (CHO) through the action of colonic bacteria relies on inoculation with the appropriate microbial population since the intestinal tract will be sterile at birth. In early life, bacteria whose substrate is lactose would be necessary for this function, although efficient digestion and absorption in the upper gastrointestinal tract (GIT) may significantly limit the necessity for such bacterial activity. Measurements in the human neonate indicate the small intestine (SI) is incapable of hydrolyzing and absorbing all dietary lactose, thus the colon may play a role in CHO conservation. Murray et al. (1991) studied conceivable routes of colonic energy retrieval from bypass dietary lactose, including mucosal metabolism and absorption as well as bacterial degradation to SCFA and subsequent absorption. Their studies indicate that in the neonatal pig lactose may be directly absorbed by colonocytes in the


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disaccharide form. The peri-natal colon is able to absorb electrolytes and amino acids (see for example Henin and Smith, 1976; Sepulveda and Smith, 1979). However we were unable to find any information describing prenatal development or activity of these functions. It is apparent that at birth the young piglet potentially has all the digestive equipment to start extra-uterine life but the system now requires activation and fine-tuning. Colostrum intake provides the activation signal required. 7.2.2

Implementation I

Colostrum stimulates intensive growth of the neonatal pig’s stomach, pancreas and small intestine within 24 hours of intake (Zabielski et al., 1999). Mucosal growth is characterised by increased DNA synthesis, an increase in protein content (Zhang et al., 1997), and a decrease in cell turnover (Moon and Joel, 1975). This is accompanied by marked expansion of villi and microvilli surface areas (Xu et al., 1992). These changes are thought to be initiated and regulated by intrinsic growth factors and hormones in the colostrum (Kelly et al., 1992; Buddington, 1993; Pacha, 2000). Cells produced by the crypts during the perinatal period rapidly replace the fetal villus enterocyte population and this coincides with the onset of changes in villus structural configuration. The finger-like villi gradually shorten and thicken throughout the suckled period (Cera et al., 1988), a process paralleled by reshuffling of hydrolase and nutrient transport activities. After birth there is a decline in amino acid absorption and monosaccharide uptake relative to tissue protein content of the enterocytes. However this is compensated for by rapid mucosal growth (Puchal and Buddington, 1992; Zhang et al., 1998; Buddington et al., 2001), such that overall capacity for nutrient uptake is unaffected or increased slightly (Zhang et al., 1997). Colostrum mediates rapid changes in intestinal hydrolase activity. Zhang et al. (1997, 1998) demonstrated colostrum-induced regional (proximal, mid and distal small intestine) and compartmental (brush border membrane vesicles and mucosal homogenate) modification of the specific activities of hydrolases within 24 hours of birth (Table 7.1). Total intestinal activities of lactase, sucrase, maltase and aminooligopeptidase are higher 24 hours post-partum than at birth, although their activities per unit of intestinal protein decrease (Zhang et al., 1997). Pre-partum endogenous secretion of cortisol is positively implicated in stimulation of these brush-border hydrolases (Sangild et al., 1995; Sangild et al., 2000). Amplification of absolute maltase and sucrase activities within 24 hours of birth is paralleled by increases in fructose transport capacity relative to glucose (Puchal and Buddington, 1992). This may seem surprising for an animal which is receiving an entirely milk

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Table 7.1. Changes from birth in specific (µmol/[min/g protein]) and total hydrolase activities in small intestine mucosa homogenate and brush-border membrane vesicles (BBMV) during the initial 24 hours post-partum. (Adapted from Zhang et al. 1997) Small intestine homogenate

Small intestine BBMV

Region

Proximal

Mid

Distal

Proximal

Mid

Distal

Specific activity Lactase Sucrase Maltase Aminoligopeptidase (AOP)

= = ↓ 6hrs ↓ 6hrs

= ↓ 6hrs ↓ 6hrs ↓ 6hrs

= = ↓ 6hrs =

↓ 6hrs* = = =

= = = =

= = = =

Hours post-partum

6

12

24

6

12

24

Total activity Lactase Sucrase Maltase Aminoligopeptidase (AOP)

↑ = ↑ =

↑ ↑ ↑ =

↑ ↑ ↑ ↑

= = = =

↑ = ↑ ↑

↑ = ↑ ↑

= no significant change in activity ↓↑ significant decrease or increase in activity * decreased at 6 hours, = at 12 hours, decreased at 24 hours

diet, but indicates that the piglet is evolutionally equipped to digest and absorb non-milk as well as milk foods almost immediately after birth. The nascent capacity to digest sucrose and maltose apparently develops independently of luminal exposure to these compounds, but is influenced by feed intake and composition. Zhang et al. (1998) examined intestinal structure and function in piglets 6 hours after birth in response to feed deprivation (FD) or gastric intubation with similar volumes of colostrum (C), milk replacer (MR) or an oral electrolyte solution (OES). In this study, total intestinal maltase activity in mucosal homogenate was elevated in C compared to FD pigs; MR and OES were intermediate but tended to be lower than in C contemporaries. Brush-border membrane vesicle (BBMV) total maltase and aminooligopeptidase activities were greater for C than OES with MR measurements falling between the two: FD values were comparable with MR and OES treatments. Treatment effects on gut morphology were not reported, however intestinal length and nominal surface area (intestinal


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circumference x length) declined in the order C/MR >OES/FD and C > MR/OES > FD respectively. Therefore it appears that intestinal hydrolase activities and intestinal enlargement are stimulated by the physical presence of material in the intestine and that such stimulation is differentially enhanced by the material’s nutritional and/or bioactive composition. Furthermore, the compositional qualities of colostrum appear to initiate development of intestinal characteristics associated with weaned pig digestive physiology. In addition to their role in promoting structural and functional development of the GIT, colostrum and milk provide the piglet with an arsenal of specific and nonspecific biologically active proteins and peptides. These factors mediate interaction between the contents of the intestinal tract and it’s epithelial surface and, subsequent to transmission across the gut wall, provide initial systemic immune protection. Comment on the immunological benefits this confers to the piglet is beyond the scope of this chapter but is addressed elsewhere in this publication. 7.2.3

Perspective 1

The transition from placental to enteral nutrition is immediate and abrupt. For it to be achieved successfully the neonate requires a competent digestive physiology within hours of birth. Three major factors ensure success. First, preliminary morphological adaptation of the tissues necessary for enteral nutrition occurs before birth. Second, development of enzyme and transport systems is pre-emptively targeted toward arrival of a known substrate package (colostrum/milk) within a given timeframe. Third, arrival of the substrate package activates up-regulation of the system and induces changes that fine-tune digestive physiology to the enteral diet. In addition, the substrate package has evolved to meet the nutritional requirement of the neonate completely. The neonate rapidly and effectively resolves the problems of adaptation to the extrauterine diet. However, commercial weaning enforces a second immediate and abrupt change to piglet diet. What are the consequences of this change, and does the piglet contend with this second transition as successfully?

7.3

The weaned pig

Natural weaning is a gradual process rather than the single episode we impose on the piglet commercially. The development of adult digestive physiology initiated by colostrum intake continues progressively during suckling and is more advanced when weaning is delayed (Hampson,1986; Miller et al., 1986; Cera et al., 1988; Kelly et al., 1991). Buddington (1993) suggested that normal progression of postweaning intestinal maturation was regulated by intrinsic timing mechanisms but was also dependent upon transition to the adult diet. This agreed with the

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comment by Kelly et al. (1992) that luminal nutrition has a profound influence on intestinal morphology at all developmental ages but is unlikely to be the ultimate cue for intestinal differentiation. 7.3.1

Commercial weaning

Intestinal maturation of the commercial piglet, weaned at 3 to 4 weeks of age, is compromised on two counts. First, the transition from lactation to adult diets is abrupt rather than progressive. The sudden and vastly different functional requirement this imposes on the intestine often results in profound reduction in nutrient intake (Rantzer et al., 1997; Le Dividich and Seve, 2000) and a transitory (5 d) failure of the piglet to meet its maintenance energy requirement (Pluske et al., 1997). Second, at commercial weaning age the developmental demands placed on the intestine by the change in dietary input generally precede the temporally induced adaptations observed in unweaned piglets by between 2 and 4 weeks. Thus, commercial weaning superimposes our own timetable of events over the natural maturation of the piglet’s digestive physiology instigating severe acceleration of the weaning process and launching the developmental program into a frantic ‘catch-up’ state. To confound this problem further, the piglet simultaneously elects not to eat and therefore becomes severely energy deficient. 7.3.2

Gastrointestinal, pancreatic and hepatic response

Differential growth of the various compartments of the gastrointestinal tract occurs following weaning. Makkink et al. (1994) reported a gradual increase in relative stomach mass (g/kg liveweight) over the 10 days after weaning but a decrease in that of the small intestine during the first three days that was not recovered until day 10. Similar small intestinal responses have been demonstrated by other workers (Cera et al., 1988; Kelly et al., 1991; Jiang et al., 2000) and appear positively related to feed intake (Makkink et al., 1994). In contrast, the relative mass of the large intestine increases rapidly during the early post-weaning period (van Beers-Schreurs et al., 1998), an effect that is independent of age of weaning (Kelly et al., 1991). The growth rates of organs associated with the GIT also change differentially relative to overall body mass following weaning. For example, relative liver mass increases significantly during the second week post-weaning, indicating increased hepatic metabolic activity (Slade and Miller, 2000). Following a period of accelerated growth during the perinatal period, pancreatic weight relative to whole bodyweight stabilises from about 13 doa (Gestin et al., 1997b). However, following weaning, and independent of age, pancreatic growth and protein accretion again become positively allometric (Peng et al., 1996). This second hypertrophic phase of pancreatic development is paralleled by enzyme


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specific changes in biosynthetic function of the organ. Briefly, the activities of chymotrypsin and elastase II relative to body weight decline dramatically, lipase increases slightly and trypsin, amylase and elastase I increase to dominate pancreatic contribution to the digestive process (Gestin et al., 1997a; Gestin et al., 1997b). Pancreatic response to weaning is inconsistent. For example, Rantzer et al. (1997) reported that adult exocrine volume, and protein and trypsin levels, were achieved within 5 days of weaning pigs at 30 doa. Conversely Cranwell (1995) reported that pancreatic enzymes were significantly depressed during the first week after weaning. Biosynthesis of specific enzymes appears to be an adaptive response to age at weaning (Gestin et al., 1997a), fat and dry matter intake (Gestin et al., 1997b), and dietary protein content (Zebrowska et al., 1983; Makkink et al., 1994). The source of protein in the diet also influences expression of pancreatic enzymes. For example, Makkink et al. (1994) found that pancreatic tissue enzyme activity was enhanced in pigs fed milk protein as opposed to soya. However, this result contrasts directly with the earlier findings of Newport and Keal (1982) comparing response to the same two proteins, but with different diets and methods of analysis. Further clarification of dietary effects on pancreatic development and enzyme expression is required. 7.3.3

Small intestine morphological response

The effects of weaning on intestinal morphology are acute. Over the last 30 years there have been numerous observations of post weaning villus atrophy and crypt hyperplasia. To summarise, reductions in the ratio of villus height to crypt depth ratio (V:C) are evident within 24 hours of weaning and are most pronounced by 3 to 5 days (Hampson, 1986; Miller et al., 1986; Cera et al., 1988). Significant increases in crypt depth may not be observed until 5 days post-weaning (Hampson, 1986) after which time V:C ratio stabilises between 1.5 and 2.0 (Hampson, 1983). The decline in V:C ratio immediately following weaning is thus primarily the result of villus shortening, an effect that is less pronounced proximal to distal along the small intestine. Figure 7.1 presents plots of least squares mean values for proximal jejunum crypt depth, villus height and V:C ratio data extracted from seven different trials reported during a period of 15 years (Hampson, 1986; Miller et al., 1986; Kelly et al., 1991; Pluske et al., 1991; Makkink et al., 1994; Pluske et al., 1996b; Jiang et al., 2000). Weaning ages, diets and days post-weaning of sampling are detailed for each reference in Table 7.2. Analysis of the data used to generate Figure 7.1 indicates the decline in villus height from d 0 (suckled) becomes significant on d 4 (P25 days after service) 4Including abortion 5Including failure to farrow and abortion 2Normal

As could be expected, reasons for culling vary with parity of the females. “True” reproductive disorders (anestrus + failure to conceive/farrow + low litter size at birth) account for nearly 40% of total culls in young sows (parities 1 and 2) and only for 17% in old ones (parity > 7); (Figure 15.1). However, when sows that are culled because of their age are excluded from the analyses, the difference in the reasons for culling between young and old sows is much smaller. For instance, it can be calculated from Norwegian data that nearly 40% of first-parity sows are culled for “true” reproductive disorders versus 34% of sows whose parity is higher than 7, when the age reason is excluded (Sehested and Schjerve, 1996). A potential limitation of studies from database analyses is the fact that definitions of removal reasons are not standardised and, very often, sows are not culled for a single reason but for several reasons. For instance, an old sow with low productivity and lameness may be culled for low mothering ability, for lameness and for its


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Figure 15.1. Influence of the parity on the reasons of culling in Landrace x Yorkshire sows (based on Sehested and Schjerve, 1996).

age. However, the producer has to choose only one reason. This may underestimate one parameter and overestimate the other. Moreover, producers may falsely diagnose reproductive failures. Geudeke (1992), for example, examined genital tracts of 5969 sows. Of the 13.7% sows that were culled for anestrus, almost 60% had normal ovaries, 16.9% had inactive ovaries and 25.3% had cystic ovaries.

15.3

Consequences of lactation and weaning on the reproductive axis

Lactation normally almost completely inhibits the activity of the reproductive axis. Weaning removes this inhibition and thus results in estrus behaviour and ovulation (reviews: Britt et al., 1985; Varley and Foxcroft, 1990; Quesnel and Prunier, 1995). Under specific conditions, lactational estrus and ovulation may occur (see further). 15.3.1

Postpartum inhibition

15.3.1.1 Long-term effects of pregnancy and farrowing Weaning piglets at birth, instead of at 3 to 5 weeks of age, results in a higher incidence of anestrus and cystic ovaries, a longer weaning-to-estrus (weaning-to-service) interval, or a reduced litter size (Peters et al., 1969; Elliot et al., 1980; Varley and Atkinson, 1985). This suggests that physiological events associated with pregnancy and farrowing have an inhibitory influence on the reproductive axis.

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Productivity and longevity of weaned sows

During the last month of pregnancy, LH secretion is inhibited by the high concentrations of progesterone synthesized by corpora lutea and probably also by the high levels of estrogens originating from the feto-placental units. Farrowing is accompanied by a drop in progesterone and estrogen concentrations and is followed by an immediate increase in gonadotropin secretion in suckled sows and in sows weaned immediately after farrowing (zero-weaned sows; Smith et al., 1992; De Rensis et al., 1993a). Therefore, postpartum anestrus in zero-weaned sows is not related to an impaired secretion of gonadotropins just after farrowing, as observed in domestic ruminants. Anestrus and cystic follicles can be due to the lack of a preovulatory LH-surge resulting from either the high levels of corticosteroids observed in early-weaned sows (Ryan and Raeside, 1991) or an impaired responsiveness to positive feedback effects of estradiol-17β at the hypothalamicpituitary level (Elsaesser and Parvizi 1980; Cox et al. 1988; Sesti and Britt 1993). This responsiveness is partially recovered between the third and the fourth weeks of lactation. Decreased responsiveness of the pituitary in early lactation may be partly related to LH stores in the pituitary gland, that are depleted just after farrowing and progressively restored during lactation (Crighton and Lamming 1969; Bevers et al. 1981). However, the pituitary answer to the positive feedback of estrogens has not been investigated in zero-weaned sows. Another long-term effect of gestation on the reproductive axis involves the uterus, which was submitted to considerable changes during gestation. The uterine involution is rapid during the first week postpartum (p.p.) but is completely achieved only within 21 to 28 days p.p. in lactating sows (Palmer et al., 1965a, b; Smidt et al., 1969). In early-weaned sows (4 days p.p.), the involution is still slower (Smidt et al., 1969). Therefore, the morphology and physiology of the genital tract may not be optimal for fertilization and blastocyst implantation in sows weaned at farrowing or shortly after, resulting in a reduced rate of gestation (and a longer weaning-to-service interval) or a reduced litter size. 15.3.1.2 Influence of suckling Mean concentrations of circulating LH are high during the two or three days following parturition and then decrease in lactating sows (Tokach et al., 1992; De Rensis et al., 1993a, b). These concentrations and the number of LH pulses remain low during early lactation, from about day 4 to 14, and gradually increase thereafter (Stevenson et al., 1981; Shaw and Foxcroft, 1985; De Rensis et al., 1993b). There is consistent evidence that suckling (stimulation of the teats by the piglets) and piglet proximity provide physical and behavioural stimuli to the sow that induce the release of neurotransmitters and opioid peptides, through neuroendocrine reflexes (review: Kraeling and Barb 1990). These factors stimulate the secretion of pituitary hormones involved in milk ejection and production (e.g. oxytocin,


389


prolactin, growth hormone, cortisol) and suppress LH secretion by inhibiting the GnRH pulse generator. The suckling-induced inhibition of LH begins only within two or three days p.p. (De Rensis et al., 1993a). It is mainly due to endogenous opioids during established lactation, whereas its development during the early p.p. period appears to be opioid-independent (De Rensis et al., 1993b, 1998a). In addition to the opioidergic system, a dopaminergic regulation of LH secretion exists during the fourth week of lactation as shown by De Rensis et al. (1998b). However, these authors provided evidence that prolactin itself was not involved in the control of the GnRH/LH secretion during lactation. This is in contradiction with the prevailing hypothesis suggesting that prolactin may partly inhibit LH release during lactation (reviews: Van de Wiel et al., 1985; Dusza and Tilton, 1990). The progressive decrease in the inhibition of LH secretion could be related to a decrease in suckling frequency and intensity over the four weeks of lactation (Pederson et al., 1998; Jensen et Recén 1989) and could be related to the increase in the pituitary LH response to GnRH as lactation progresses (Bevers et al., 1981; Rojanasthien et al., 1987a). Data on the variation in FSH secretion during lactation are less consistent. Within the three days following parturition, FSH concentrations do not vary with time and are similar in suckled and zero-weaned sows (De Rensis et al., 1993a). From the second week of lactation onwards, a continuous increase in plasma FSH has been observed by Stevenson et al. (1981) and De Rensis et al. (1993b). Ovariectomy during lactation is accompanied by an increase in FSH concentrations without affecting LH secretion (Stevenson et al., 1981), demonstrating that FSH secretion is more controlled by the ovarian negative feedback (presumably by inhibin) than by suckling. In suckled sows, large follicles (> 5 mm) are present in the ovaries during the first week p.p. and are replaced by small and medium-sized follicles (3-4 mm) during the second week (Crighton and Lamming, 1969; Kunavongkrit et al., 1982; Rojanasthien et al., 1987b). During the third and fourth weeks of lactation, follicular growth resumes as a consequence of the progressive increase in LH pulse frequency but most follicles are < 5 mm in diameter (review: Britt et al., 1985). Because of the inhibition of follicular growth, circulating estrogens are generally low (Baldwin and Stabenfeldt, 1975; Kirkwood et al., 1984; Prunier et al., 1993). Beside this general pattern of follicular growth during lactation, Lucy et al. (2001) reported differences in follicular development between sows before weaning using ultrasonography. Sows can have relatively inactive ovaries (follicles less than 2 mm in diameter) or have large follicles present.

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Ovulation can be induced during lactation by administration of exogenous gonadotropins (review: Britt et al., 1985). Reduced follicular growth during lactation is thus primarily due to low gonadotrophic signal. However, other factors can act directly at the ovarian level for instance, by modulating the follicular responsiveness to gonadotropins. 15.3.1.3 Influence of the metabolic status During lactation, sows are usually fed ad libitum or close to ad libitum and their voluntary feed intake increases during the first three weeks postpartum (review: Dourmad, 1988). Energy requirements for milk production simultaneously increase and peak during the third week of lactation (Noblet and Etienne 1986). Voluntary feed intake depends on numerous endogenous and environmental factors (review: Dourmad, 1988; Eissen et al., 2000) and is often not sufficient to meet the high energy and nutrient requirements for milk production. This appears to be particularly true in high-yielding multiparous sows and in most first-litter sows, that have a lower feed intake than multiparous sows but a relatively high milk production (> 7-8 kg/day). The energy balance of these sows is thus negative throughout lactation. A slight catabolic state does not affect gonadotropin secretion, even in first-litter sows, as evidenced in lactating sows that consume between 80 and 90% of the metabolic energy requirements for maintenance and milk production (review: Prunier and Quesnel, 2000). Moreover, making sows anabolic during lactation, by superalimentation via a stomach cannula, did not alleviate the negative impact of suckling on LH secretion around weaning and did not improve reproductive performance after weaning, as shown by Zak et al. (1998). In their experiment, however, the control sows already had a good reproductive performance. In contrast, a strong catabolic condition during lactation has been clearly demonstrated to inhibit the activity of the hypothalamo-pituitary complex in primiparous sows. Indeed, restriction of feed (Reese et al., 1982; Zak et al., 1997a; Quesnel et al., 1998a), energy (Armstrong et al., 1986a; Koketsu et al., 1996a) or protein (King and Martin, 1989; Jones and Stahly, 1999a; Yang et al., 2000a) generally inhibit the secretion of LH during lactation and delay estrus after weaning. Lactation induces metabolic adaptations that favour the preferential drive of nutrients towards mammary glands. Concentrations of prolactin, growth hormone (GH), insulin-like growth factor-I (IGF-I) and insulin are relatively high during lactation due to suckling and high feed consumption. During the course of lactation, prolactin, GH and IGF-I decline slowly, possibly due to attenuated intensity of suckling stimuli (Rojkittikhun et al., 1993; Schams et al., 1994). Plasma glucose, insulin, IGF-I and leptin also decrease throughout lactation in those sows with increasing nutritional deficit and body reserve mobilization (Prunier et al., 1993; Messias de Bragança and Prunier, 1999; Van den Brand et al., 2001; Prunier et al., 2001). Metabolic adaptations have been extensively described in primiparous sows submitted to a


391


severe level of nutritional restriction during lactation. Compared with well-fed sows, feed-restricted sows have lower plasma insulin, IGF-I and leptin but higher plasma NEFA and GH (Koketsu et al., 1996a; Zak et al., 1997a; Quesnel et al., 1998a; Mao et al., 1999). Obviously, the GH-IGF-I axis becomes uncoupled. Together with low insulin, this favors maternal catabolism. There is increasing evidence that these changes in metabolites and metabolic hormones signal to the reproductive axis the changes in metabolic state (reviews: Booth, 1990; Pettigrew and Tokach, 1993; Prunier and Quesnel, 2000). Amongst these potential mediators, glucose, insulin and IGF-I could play a preferential role. A strong reduction in glucose and/or insulin has been associated with inhibited secretion of LH in prepuberal gilts submitted to severe feed-restriction or to experimentally-induced glucose restriction (Booth, 1990; Barb, 1999) and in diabetic gilts (Angell et al., 1996). In lactating sows, LH pulsatility around weaning has been positively related either to insulin (Quesnel et al., 1998b) or IGF-I (Van den Brand et al., 2001). Feeding a carbohydrate-rich diet increases LH pulsatility during early lactation (day 7) but not later in lactation (days 14 or 21) despite higher post-feeding insulin levels at both stages (Kemp et al., 1995; Van den Brand et al., 2000a). Evidence is still lacking that reduced insulin alters LH pulses in catabolic lactating sows. At the ovarian level, consistent evidence exists that insulin and IGF-I stimulate follicular responsiveness to gonadotropins and folliculogenesis (Adashi et al., 1992). Therefore, reduced concentrations of insulin and IGF-I in plasma and/or follicles observed in feedrestricted lactating sows (Quesnel et al., 1998a, b) may reduce the ovarian response to the gonadotropic stimulation at weaning and alter subsequent follicular development. Indeed, Quesnel et al. (1998a, b) have observed that feed restriction during lactation induces a reduction in insulin, IGF-I and LH concentrations at day 27 of lactation. This results in a concomitant decrease in the number of follicles measuring at least 4 mm in diameter and in the proportion of healthy 1-3 mm follicles at weaning (day 28). Similarly, Clowes et al. (1999) have shown that protein restriction of primiparous sows has a negative influence on the number of large follicles (4 to 6 mm) on day 23 of lactation. Moreover, follicular fluid from these sows has a lower potential to support in vitro nuclear maturation of oocytes. 15.3.2

Removal of the inhibition of the hypothalamic-pituitary-ovarian axis at weaning

Weaning piglets suppresses the inhibitions originating from the suckling stimuli and from the potential catabolic status. This results in an immediate and transient increase in mean concentrations of LH and LH pulse frequency ovulation (reviews: Britt et al., 1985; Varley and Foxcroft, 1990; Quesnel and Prunier, 1995). Increased secretion of FSH in response to weaning has been observed in some experiments (Cox and Britt, 1982; Shaw and Foxcroft, 1985) but not in others (Stevenson et al., 1981; Edwards and Foxcroft, 1983; Foxcroft et al., 1987). This divergence between

392

Weaning the pig


LH and FSH profiles around weaning supports the existence of different controls of gonadotropin secretion: LH secretion mainly depends on suckling and lactation influences, whereas FSH mainly depends on ovarian negative feedback. The increase in gonadotropin secretion at weaning stimulates follicular growth and maturation, as evidenced by the immediate increase in the number and size of large follicles (diameter > 5 mm) after weaning (Palmer et al., 1965a; Cox and Britt, 1982; Armstrong et al., 1986b). Relatively high concentrations of estradiol-17β and testosterone are measured in follicles 24-48 hours after weaning (Foxcroft et al., 1987; Killen et al., 1992). Plasma estradiol-17β rises significantly within 24-48 hours after weaning in sows with a normal return to estrus (Rojanasthien, 1988; Tsuma et al., 1995). Similarly, concentrations of inhibin in both plasma and follicular fluid progressively rise during the first two days after weaning (Trout et al., 1992). As during the follicular phase of the estrous cycle, high circulating concentrations of estradiol-17β induce estrous behaviour, the preovulatory surge of gonadotropins and then ovulation. However, a marked variability between sows is observed in post-weaning follicular development (Foxcroft et al., 1987). It is likely that this is related to the variation in the weaning-to-estrus interval and/or in the ovulation rate. Stimulation of LH secretion at weaning occurs in most sows, even when they were strongly catabolic during lactation (Zak et al., 1997a; Quesnel et al., 1998a). The amplitude of the increase is not necessarily related to the degree of inhibition of LH during lactation (Zak et al., 1997a). The interval between weaning and estrus was mainly related to mean or episodic secretion of LH during mid-lactation or just before weaning in several experiments in which primiparous sows belonged to a single population (Shaw and Foxcroft, 1985; Tokach et al., 1992) and in which LH secretion during lactation was altered by nutritional treatments (Armstrong et al., 1986a; Koketsu et al., 1996a; Zak et al., 1997a). This suggests that the degree of inhibition of LH during lactation influences the resumption of ovarian activity after weaning. However, several papers also describe a positive relationship between postweaning LH and subsequent WEI. For example, Van den Brand et al. (2000a) found that this relation was linear for sows with a low number of LH pulses (< 8 pulses/12 h) whereas sows with a higher number of LH pulses had the same short WEI. Postweaning ovarian activity could also be modulated by the concentrations of metabolic hormones during lactation (see 15.3.1) per se. Supporting that, alterations in post-weaning ovulation rate and/or embryo survival were reported regardless of variations in LH secretion around weaning (feed restriction: Zak et al., 1997a, b; lysine/protein restriction: Mejia-Guadarrama et al., 2001). Based on the kinetic and hormonal regulation of follicular growth, it is likely that FSH and LH induce follicle recruitment immediately after piglet removal. These follicles that ovulate 4 to 7 days later are healthy follicles measuring 2-3 mm at weaning. It is probable that their number will influence the ovulation rate at first post-weaning estrus and that their


393


characteristics (‘quality’) could have consequences on the oocyte development and/or on the luteinization process of the follicular cells, thus modulating fertilization rate and embryo survival. In addition, the hormonal background existing after weaning may influence the process of recruitment and maturation of the preovulatory follicles. Therefore, both lactational and post-weaning events may act on the reproductive performance of primiparous and multiparous sows. However, if the lactation period does not have profound negative effects on LH secretion or follicle development, no detrimental effects of lactation on post-weaning performance are expected and effects of post-weaning events will be limited.

15.4

Variation in reproductive performance: extent and sources of variation

15.4.1

Components of fertility and prolificacy

Fertility and prolificacy of sows can be influenced by many factors, including internal (e.g. genetic factors, parity, body reserves, milk production) or environmental factors (e.g. stress, light, ambient temperature, light, housing) as well as management decisions (e.g. length of lactation, level of feeding). Field data give information especially on the effects of parity, genotype, litter size, length of lactation and season on the weaning-to-estrus interval, litter size and farrowing rate or longevity of sows (e.g. Koketsu et al., 1997a, b; Le Cozler et al., 1997; Lucia et al., 2000). Information on the influence of internal or environmental factors acting during lactation on the underlying components of farrowing rate and litter size, that is ovulation rate, fertilization rate, embryo survival and fetal survival comes from experimental herds. In the following paragraphs, effects of factors acting either during lactation or after weaning on the reproductive function will be summarised. However, it should be noticed that most of field or experimental data concern factors acting during lactation. 15.4.2

Influence of nutritional factors

15.4.2.1 Influence of nutrient supply Feed supply during lactation has often been found to affect WEI, and also ovulation rate and embryo survival, resulting in effects on pregnancy (farrowing) rate and litter size but the effects can be very variable from study to study (Table 15.3). A low feeding level during lactation increased WEI in most studies, but significantly in only 4 out of 8. It significantly decreased ovulation rate in only one study, embryo survival in three studies and pregnancy rate in two studies. Therefore, effects of low feeding levels on WEI are more consistent than their effects on ovulation rate, embryo survival and pregnancy rate. Even in modern crossbred primiparous sows (studies

394

Weaning the pig


in Table 15.3 from 1997 onwards) very different effects can be found: no effects (Quesnel and Prunier, 1998); effects on WEI only (Zak et al., 1998); effects on ovulation rate and embryo survival (Zak et al., 1997a), or effects on ovulation rate only (Van den Brand et al., 2000a). It is not easy to verify the causes of this variability.

Table 15.3. Influence of feed supply during lactation or after weaning on liveweight at weaning (LW, kg), subsequent weaning-to-estrus interval (WEI, days), ovulation rate, embryo survival at day 25 to 35 of pregnancy (ES) or litter size (LS) in brackets and, pregnancy rate (PR) or farrowing rate (FR) in brackets. Feed sup.(%)a LW at weaning WEI

Ovulation rate ESb (LS)

PR (FR)

Low

High Low High

Low

High Low High

Low Sourcec

During lactation 85 40 135 85 45 ~200 80 40 ~177 80 45 199 80 45d 179 d 45 90 60 210 85 50 163 79 67 152

108 ~180 ~164 176 162 172 194 137 145

7.6 4.3 6.0 5.9 3.7

(9.7) 83 83 85 88

5.7 4.2 5.1

13.5 18.6 17.7 16.7 15.4* 15.4* 20.7 15.6 16.2†

(89) 69* 77† 62* 100 100 100 -

After weaning 285 115 122 245 155 199

121 199

9.1 8.2 15.2 13.4 14.1 14.6 6.0 5.9 16.6

High

Low

High

19.9* 14.4 5.8* 18.1 8.9* 17.6 7.5 16.2 5.6 19.9 5.1 5.9 19.2 6.3* 14.4 5.7 18.1

83 68

(9.7) 68† 72* 64* 87 64* 72 68

(79) 90 89 82 100 100 -

14.8 13.2* (10.0) (9.5) (76) 16.2 78 85 87

(1) (2) (3) (4)d (5) (5) (6) (7) (8)

(9) (92) (1) 82 (4)d

a

For effects of feed supply during lactation, animals were restricted after lactation. For effects of feed supply after lactation, animals were full fed during lactation. Feed supply (%) is the estimated ratio between metabolic energy intake and requirements for maintenance in weaned sows and for maintenance + milk production in lactating sows (see Prunier and Quesnel, 2000). b (1) King and Williams, 1984 (2) Kirkwood et al., 1987 (3) Kirkwood et al., 1990 (4) Baidoo et al., 1992 (5) Zak et al., 1997a (6) Quesnel and Prunier, 1998 (7) Zak et al., 1998 (8) Van den Brand et al., 2000a (9) Den Hartog and van der Steen, 1981. c Percentage of viable embryos to number of corpora lutea. d Low feed intake (5% of ME requirements) was imposed during the first three weeks of lactation (first line of data) or last (4th) week of lactation (second line of data). * P < 0.05, † P < 0.05.


395


It is dependent on the reproductive performance of the control group (which is quite different from experiment to experiment), and may be related to factors such as body condition at farrowing, litter size, litter gain, lactation length, degree of feed restriction, weight loss during lactation etc. It seems reasonable to suggest that a more severe energy deficit during lactation will have larger effects on WEI, ovulation rate and embryo survival. Data from King and Dunkin (1986a) corroborate this relationship between the degree of feed restriction and the effect on WEI. They compared 6 levels of feed consumption during lactation of first-litter sows, and observed that the proportion of sows exhibiting estrus within 8 days of weaning was 83% at the highest feeding level and decreased linearly with daily feed intake to only 8%. Contrarily, they did not find any influence of the feed intake on ovulation rate. This may be due to the fact that the WEI was relatively long in all their experimental groups. Data from Table 15.3 show that the decrease in the ovulation rate in restricted sows was significant or close to significance only when weaning-to-estrus interval was short (Zak et al., 1997a; Van den Brand et al., 2000a). Therefore, factors imposed during lactation have decreasing effects on the postweaning ovulation rate when the WEI increases. Such a conclusion can not be drawn regarding the effects of feed restriction on embryo survival and pregnancy rate. The effects of lactational feed intake on ovulation rate seem to be associated with altered follicular development at the time of weaning, which itself may depend on the hormonal background at that time (see 15.3.2). Data obtained in gilts by Soede et al. (2000) corroborate this hypothesis. These authors found that a feed restriction of 60% of ad libitum feed intake during the last week of progesterone dominance (Regumate®) resulted in fewer large follicles at the last day of treatment (follicles larger than 4.5 mm/ovary: 4.2 vs. 9.5) and in lower subsequent ovulation rate (14.8 vs. 17.2) without any influence on the interval between Regumate® cessation and ovulation. Almeida et al. (2000) restricted feed intake during the second week of the luteal phase and did not find effects on ovulation rate, but found significant effects on progesterone rise during early pregnancy and subsequent embryo survival rate (68% vs 83%). Similarly, the hormonal background existing during lactation may influence quality of the oocytes and hence the subsequent embryo survival and pregnancy rate. Analyses of farm data have shown that the feed intake pattern during lactation is another important factor influencing subsequent reproductive processes. Farm data on feed intake patterns were analyzed by Koketsu et al. (1996b, c) who distinguished 6 feed intake patterns: Rapid (rapid increase in feed intake after farrowing, 23% of lactating sows); Major (major drop in feed intake during lactation, 33% of sows); Minor (minor drop, 28% of sows); LLL (low feed intake throughout lactation, 1% of sows); LHH (low feed intake during the first week then increasing for the remainder of lactation, (1% of sows); and Gradual (gradual increase in feed intake throughout lactation, 15% of sows). Analyses of subsequent reproductive

396

Weaning the pig


performance revealed that sows showing either a rapid or gradual increase in feed intake with no drop (or either a minor drop in feed intake) during the course of lactation had the lowest weaning-to-conception interval and had a lower risk to be culled due to anestrus. In sows that show a marked drop in feed intake at any time during lactation, reproductive output was decreased. The authors concluded that both the average daily feed intake and the feed intake pattern influenced reproductive performance. Experimental data also show that restricted feeding during different parts of lactation differentially affect reproductive performance. In first-litter sows, Koketsu et al. (1996a) restricted energy intake during the whole lactation or during either the first, second or third week of lactation (diets were adjusted to ensure that energy intake was restricted by 60%, but lysine intake was not restricted). The rather severe restriction of energy intake during the second, third or whole lactation significantly increased WEI (from on average 9 days to 18 to 23 days), whereas restriction in the first week of lactation resulted in an intermediate WEI of on average 14 days. No other parameters for reproductive performance were assessed. Zak et al. (1997a) also varied the timing of feed restriction in primiparous sows weaned at 4 weeks of lactation. Sows were fed to appetite (= “control” group) or were submitted to feed restriction (about 50% of ad libitum intake) either between parturition and day 21 (= group “refed”) or between day 22 and day 28 (group “restricted”). In this experiment, “refed” sows showed a significant increase in WEI (from 3.7 to 5.6 days) and a decrease in ovulation rate (from 19.9 to 15.4) but embryo survival was not affected (from 88 to 86), whereas “restricted” sows showed an increase in WEI (to 5.1 days), and decreases in ovulation rate (to 15.4) and embryo survival (to 64 %). In a second experiment using a similar protocol, Zak et al. (1997b) compared the ability of the oocytes of the 15 largest follicles to mature in vitro as well as the ability of the follicles > 3 mm to support oocyte nuclear maturation. Sows in the “restricted” group had fewer oocytes to mature in the Metaphase II stage of meiosis than “refed” sows. Further, control oocytes matured less well in the follicular fluid obtained from the ovarian follicles of the “restricted” sows than of the “refed” sows. However, data showing that the ability of the ovocytes to mature in vitro is closely linked to their ability to mature in vivo are still missing. Data concerning the effects of feed supply after weaning on the subsequent reproductive performance are scarce. The only significant effect observed was a lower ovulation rate in restricted sows in one study (Table 15.3). This effect may be related to an influence of the hormonal background existing after weaning on the recruitment process (see 15.3.2). Indeed, ovulation rate can be increased by insulin treatment after weaning which reduces the rate of atresia of selected follicles (for review: Cox, 1997).


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15.4.2.2 Influence of the composition of the diet Proteins Protein demand during lactation is high because of the protein demand for milk production. The first limiting essential amino acid in most diets is lysine, and daily lysine intake is therefore often taken as a primary determinant of lactation performance. Low protein intake during lactation results in mobilization of significant amounts of maternal body protein and in decreased milk production (Jones and Stahly, 1999b). Numerous experiments have shown that a low protein intake during first lactation (but with high energy intake) increases the subsequent WEI (20 vs. 11 days in King and Williams, 1984; 13.9 vs. 8.4 in Jones and Stahly, 1999a) and decreases the percentage of sows expressing estrus within 8 days from weaning (41 vs. 59% in King and Dunkin, 1986b; 33 vs. 83 % in King and Martin, 1989) or within 7 days from weaning (60 vs. 88 % in Brendemuhl et al., 1987) without clear effect on ovulation rate or litter size. In contrast, in two more recent experiments, protein/lysine restriction had no clear influence on the interval between weaning and prestrus (Yang et al., 2000b) or estrus (Mejia-Guadarrama et al., 2001), but affected follicular development and/or ovulation rate. Indeed, ovulation rate was lower at the postweaning estrus in restricted compared to control sows (20.0 vs. 23.4, Mejia-Guadarrama et al., 2001). Moreover, protein/lysine restriction during lactation retarded growth of preovulatory follicles collected at the postweaning prestrus and reduced their ability to support oocyte maturation (Yang et al., 2000c). Long term effects of protein/lysine deficiency during lactation have been tested by Yang et al. (2000b). They compared five levels of lysine (0.60, 0.85, 1.10, 1.35 and 1.60%) over three successive parities. Increasing dietary lysine/protein linearly decreased voluntary feed intake; e.g. in the first-litter sows from 5.4 to 4.6 kg. In their study, dietary lysine did not affect WEI (which was on average 5.8, 4.7 and 4.1 days for parity 1, 2 and 3, respectively) or farrowing rate (75.2%, 74.8% and 84.4% for parity 1, 2 and 3, respectively). However, lysine levels during lactation affected subsequent litter size, the effect depending on parity: second litter size decreased linearly with the increase in dietary lysine during first lactation whereas, third and fourth litter sizes were lowest in sows receiving 0.85 g of lysine/day. Numerous authors have used two-factorial designs in order to test whether the effects of protein and energy intakes during lactation on reproductive performance may interact (King and Williams, 1984, King and Dunkin, 1986b; Brendemuhl et al., 1987). Results show that the effects of protein intake on reproduction were rather similar at the high and low level of energy intake suggesting that there was no interaction between energy and proteins. It has been suggested that increasing lysine/protein intake in lactating sows above the nutritional requirements could improve the reproductive performance after

398

Weaning the pig


weaning. Some experiments support this hypothesis (reduced WEI: Wilson et al., 1996; increased litter size: Tritton et al., 1996) but not others (littersize: Touchette et al., 1998; Yang et al., 2000b; hormone profiles during lactation: Yang et al., 2000a; follicular maturation at proestrus: Yang et al. 2000c; WEI: Yang et al., 2000b). Therefore, no or only little improvement can be expected from high protein/lysine regimen during lactation. Starch/Fat Increasing the energy content of sow lactational diets may reduce mobilization of body stores during lactation even though a decrease in feed intake is often observed. Indeed, high fat diets allowed total ME intake to increase by 3 to 32% (12% as a mean) in high-parity sows (Drochner, 1989) and by on average 4.4 MJ (less than 10% fat added) to 6.5 MJ (more than 10% added fat) (Pettigrew and Moser, 1991). Van den Brand et al. (2000c) measured energy and protein balances in primiparous, isocalorically fed sows with diets containing 13.5% fat as compared to diets with 3.4% fat at two different feeding levels. At high feeding levels, the fat-rich diet resulted in higher body fat loss without any clear effect on reproductive performance (Table 15.4). Therefore, fat-rich diets do not reduce mobilization of body stores, but in fact increase the mobilization of body stores and thus are not expected to improve reproductive performance in practice. However, it is conceivable that in circumstances where the voluntary feed intake is very low (e.g. high ambient temperatures), the extra uptake of energy when using fat-rich diets will be beneficial for the sows.

Table 15.4. Effect of feeding level and fat level of the diet on partitioning of energy in first-litter sows during a 21 day lactation period (based on Van den Brand et al., 2000a, b, c). Energy intake/day

62.8 MJ ME

Diet

Fat

Starch

Fat

Starch

Sow losses during lactation Protein (g/d) Fat (g/d) WEI (h) Ovulation rate Embryo survival (%)

50 584a 123 17.9u 75

31 401b 122 18.2u 66

69 511a 152 15.5v 65

75 521a 130 16.9v 70

ab uv

47.1 MJ ME

P < 0.05 P < 0.10


399


In the experiment of Van den Brand et al. (2000c), a starch-rich diet was expected to be beneficial for reproductive performance since one of the important mediators between nutrition and reproduction could be insulin (see 15.3.1.3.). The starchrich diet was found to result in a higher and more prolonged insulin release (Van den Brand et al., 1998). However, neither weaning-to-estrus interval, nor ovulation rate, nor peri-estrus hormone profiles, nor embryo survival during subsequent pregnancy were influenced by the diet (Table 15.4). 15.4.2.3 Influence of body stores As has been discussed in 15.4.2.1., the level of feed intake during lactation has important consequences for subsequent reproductive performance. An important question is whether these effects are influenced by the levels of body stores, either at the onset of lactation or at the end of lactation. Several studies have been performed trying to reveal the relative importance of factors such as body stores of protein and/or fat at farrowing, body stores of protein and/or fat at weaning, protein losses during lactation and fat losses during lactation for post-weaning reproductive performance. Effects of body condition at farrowing have mostly been studied in relation to weaning-to-estrus interval and in first-litter sows. Results are ambiguous: Mullan and Williams (1989), Weldon et al. (1994), Le Cozler et al. (1998 and 1999) found no effect of body condition on WEI; Prunier et al. (2001) did not observe alteration in gonadotropin release and ovarian development at the end of lactation; Yang et al. (1989) and Dourmad (1991) found a longer WEI in thin sows, whereas Xue et al. (1997) found a longer WEI in fat sows. In fact, there is a negative relationship between fatness at farrowing and appetite during lactation. Therefore, it is likely that the influence of body stores at farrowing on the post-weaning performance depends on their negative impact during lactation, being inhibitory only when this effect is very marked as illustrated by the following experiments. Firstly, Xue et al. (1997) compared two levels of feeding during gestation (46 vs. 27.2 MJ ME/day) which produced backfat depth at farrowing of 30.5 and 25.5 mm in average. During lactation, spontaneous feed intake was highly reduced in fatter sows (-29 %) and resulted in a similar body weight at weaning at day 21 (approximately 163 kg), but backfat was still higher in sows which were fatter at farrowing (23 vs. 17.5 mm). At day 15 of lactation, basal and peak levels of insulin after glucose infusion were lower in fatter sows. At days 7 and 14 of lactation, LH release was impaired in the fatter sows and the WEI tended to be longer (8.0 vs. 6.4 days). The authors suggest that the increase in WEI in the sows with high gestational energy intake was a result of the low feed intake during lactation through an interaction of insulin with LH-secretion. Secondly, Le Cozler et al. (1998, 1999) compared two levels of feeding during rearing which resulted in two levels of backfat at farrowing (23.7 vs. 17.4 mm in 1998; 22.4 vs. 20.7 mm in 1999). They observed

400

Weaning the pig


that feed intake was only slightly reduced during lactation (- 8% in Le Cozler et al., 1998; -3 % in Le Cozler et al., 1999) in fatter sows and did not show any influence of fatness on the WEI and subsequent litter size. Yang et al. (1989) tried to determine the respective effects of body stores at parturition and at weaning on reproductive performance in sows over four parities. To achieve this, two levels of feeding were used during gestation in order to reach 12 or 20 mm of backfat (P2) at farrowing. These levels were combined with two levels of feeding (ad libitum or restricted at 3 kg/day) during lactation and two sizes of sucking litters (6 vs. 10 piglets). All three factors significantly influenced backfat at subsequent weaning, changes in backfat during lactation, sow live weight at weaning and changes in sow live weight during lactation. Sows which were fatter at farrowing had a lower ad libitum feed intake during lactation over the 4 parities (-23%) but this difference was much lower in first-litter sows (-7%). In these latter sows, WEI was influenced by fatness at parturition and by feed intake during lactation but not by litter size. A significant relationship was also found between fatness at weaning (P2 in mm) and WEI (WEI = 26.6 (s.e. 4.7) - 1.28 (s.e. 0.39) x P2 (r.s.d. 3.5)). No other relationships of body stores with WEI were presented. When looking at the percentage of primiparous sows in estrus within 8 days after weaning, there was a strong interaction between fatness at farrowing and feed intake during lactation: this percentage was highly reduced only in sows which were thin at farrowing and were restricted during lactation (30 vs. 83% in average for the three other groups). In later parities, only litter size during lactation influenced WEI (6.0 vs. 8.0 days for 6 vs. 10 piglets). In summary, reproductive performance of sows after weaning may be influenced by fatness at farrowing in interaction with feed intake during lactation. Extremely fat and extremely thin primiparous sows should both be avoided. 15.4.2.4 Conclusion In most studies, return-to-estrus after weaning is delayed by low feed intake and by low energy or protein intakes. For ovulation rate, the effects are less clear: in older studies, no effects on ovulation rate were found and in recent studies, ovulation rate was frequently decreased by both feed and protein restriction. For oocyte maturation and embryonic survival, data are scarce and comes only from studies published in the last five years. Both feed and protein deficiency during lactation can have negative effects on these parameters.


401


15.4.3

Influence of lactational characteristics

15.4.3.1 Litter size Reducing litter size decreases the suckling intensity and lowers the risk of nutritional deficit and hence may improve the reproductive performance of sows after weaning. Indeed, in their experimental farm, Vesseur et al. (1994b) observed that sows with a larger litter size at weaning had a longer WEI (8.3 days vs. 7.5 days for sows weaning 11-12 vs. 7-8 pigs respectively). However, the percentage of anestrous sows which were treated with gonadotropins to induce heat was not influenced by the litter size at weaning. Similarly, in a retrospective study based on farm data, Koketsu et al. (1997a) observed that neither the percentage of anestrous sows nor the percentage of sows with return to heat after service were influenced by litter size at weaning. On the overall, the effect of litter size during lactation on reproductive performance after weaning seems to be weak. However, it should be noted that sows with larger litter size at weaning have probably larger litter size at farrowing and hence higher breeding values and a better potential for reproduction. Suckling intensity during lactation can be manipulated by removal of the heaviest piglets a few days before full weaning (= split-weaning) or by separating the whole litter from the sow during a part of each day for the last days of lactation (= interrupted suckling). It generally results in a shorter weaning-to-estrus interval (review: Matte et al., 1992). The reduction is more marked with the interrupted suckling but this latter method is more laborious and time-consuming. Moreover, estrus may occur during lactation that will complicate management of the sows. Therefore, in recent years, only the effect of split-weaning on reproductive performance has been evaluated. Data from Vesseur et al. (1997) did not show any clear effect of split-weaning (4-5 piglets out of 10-12 during the 4th week p.p.) on the WEI, nor on the farrowing rate and subsequent litter size in parity-1 sows. However, they observed a shorter WEI (4.6 vs. 5.4 days for sows returning to estrus within 15 days) and a higher farrowing rate (97.2 vs. 86.3%) in parity-2 sows submitted to split-weaning compared to control sows. 15.4.3.2 Length of lactation Increasing the length of lactation from about 10 to 30 days results in a decrease in the weaning-to-estrus interval and a raise in subsequent litter size and farrowing rate in both primiparous and multiparous sows. The effect on litter size is more marked in multiparous sows (Figures 15.2A and 2B). As a consequence, the weaningto-conception interval is reduced but this reduction is not sufficient to compensate for the increase in the lactation length and the farrowing-to-conception interval increases (Figure 15.3). The positive effect of the duration of lactation on fecundity and prolificacy can be explained by several phenomena. Firstly, it may be assumed

402

Weaning the pig

Litter size (total born)

Weaning-to-estrus interval (days)


Primiparous Multiparous

A

12

Primiparous Multiparous

10 8 6 4 10

15

20

25

30

15

20

25

30

B

13 12 11 10 10

Duration of lactation (days)

Figure 15.2. Influence of the length of lactation on the weaning-to-estrus interval (A) and on the farrowing-to-conception interval (B) in primiparous and in multiparous sows (redrawn from Le Cozler et al., 1997: ; Koketsu and Dial, 1998: ).

Farrowing-to-conception interval (days)

45

Primiparous

Multiparous

40 35 30 25 10

15

20

25

30

Duration of lactation (days)

Figure 15.3. Influence of the length of lactation on the subsequent farrowing-toconception interval after weaning (adapted from Le Cozler et al., 1997).


403


that the recovery of the uterus from the previous gestation is more advanced at the new conception which will allow a better fertilization rate and embryo survival (see 15.3.1.1). Secondly, it seems that the percentage of sows that does not ovulate at first estrus is abnormally high in case of short lactations (Table 15.5). Thirdly, the reduction in the WEI associated with the increase in the length of lactation itself has positive effects on litter size (see 15.4.5). Surprisingly, in sows with very short lactation (7 to 10 days), litter size is higher than in sows with short lactation (11 to 16 days) as shown by Marois et al. (2000). This can be explained by a longer farrowing-to-conception interval and hence a better uterine recovery at mating.

Table 15.5. Effect of the length of lactation on the percentage of sows ovulating within 8 days after weaning and on the percentage of these sows that ovulate (based on Knox et al., 2001). Length of lactation (days)

Sows in estrus (%) Sows ovulating (%) ab

< 17

17-24

25-31

> 31

35a 78a

94b 92b

98b 98b

96b 96b

P < 0.05

15.4.4

Influence of the physical and social environment

15.4.4.1 Climatic environment Even though the domestic pig is not a true seasonal breeder, it manifests variations in reproductive performance throughout the year. Prolonged intervals between weaning and subsequent estrus, ovulation and fertilization have been reported during summer and early fall, the influence of season being more pronounced in primiparous compared to multiparous sows (review: Prunier et al., 1996). The highest remating rate and lowest farrowing rate are also observed for sows served in summer whereas season has no clear effect on litter size (Koketsu et al., 1997a, b; Hughes, 1998; Tummaruk et al., 2000). Lower feed intake during lactation in summer is not sufficient to explain the delayed return to estrus after weaning: in their retrospective analysis of farm data, Koketsu et al. (1997b) observed that the weaning-to-mating interval was still prolonged during summer after adjusting data for feed intake.

404

Weaning the pig


Long photoperiod and high ambient temperatures are the main environmental cues, which may influence the reproductive activity. Results concerning the influence of photoperiod variation using abrupt variations of light duration around farrowing or weaning are controversial. In contrast, when progressive patterns of variation are applied during gestation and lactation, it is clear that increasing light duration has a detrimental influence on the return to estrus after weaning compared to decreasing light duration (review: Prunier et al., 1996). Numerous experiments have shown that high ambient temperatures increase the WEI and its variability especially in first-parity sows (review: Prunier et al., 1996). Reduction in appetite and subsequent increase in the nutritional deficit during lactation explains only partly this negative effect of high ambient temperatures on the reproductive function (Prunier et al., 1997; Messias de Bragança et al., 1998). Nutritionally-independent variations in the secretion of hormones implied in the control of thermoregulation (for example thyroid hormones and cortisol) and able to act on the hypothalamopituitary-ovarian axis are probably involved. 15.4.4.2 Housing environment Data related to the influence of the housing system during lactation or around weaning on the subsequent reproductive performance of sows are scarce and relatively old. Grouping sows during lactation induces fertile estrus during lactation which is not desirable (Bryant et al., 1983). Penning sows in groups at weaning has no or a positive effect on the weaning-to-estrus interval and on litter size (Hemsworth et al., 1982; Lynch et al., 1984; Schmidt et al., 1985). It has no effect (Hemsworth et al., 1982; Schmidt et al., 1985) or a negative effect (Lynch et al., 1984) on the farrowing rate. However, more data are necessary to conclude definitively whether grouping sows at weaning will improve or deteriorate reproductive performance. 15.4.4.3 Boar effect The boar is well known to have stimulatory effects on the reproductive function of female pigs. Indeed, boar exposure of sows daily during the last 7/8 days of lactation reduces the weaning-to-estrus interval (Walton, 1986; Newton et al., 1987), but the effect seems to be more marked in multiparous than in primiparous sows (Walton, 1986). Similarly it has been observed that in sows with daily boar contact after weaning, estrus and ovulation occur earlier (Hemsworth et al., 1982; Walton, 1986; Pearce and Pearce, 1992) and in a higher proportion of sows (Langendijk et al., 2000). However, some discrepancy exists. Hughes (1998), for example, did not observe any effect of boar contact(s) but in his study the return to estrus after weaning occurred very early even in sows without any boar contact (5.5 days). When farrowing rate and litter size were measured, these parameters were not influenced by boar exposure (Hemsworth et al., 1982; Hughes, 1998).


405


15.4.5

Relationships between WEI, litter size and farrowing rate

Several analyses of field data have related the WEI to subsequent litter size and farrowing rate (Leman, 1990; Vesseur et al., 1994a; Le Cozler et al., 1997; Steverink et al., 1999; Tummaruk et al., 2000; Figure 15.4). The analyses show that an increase in WEI from 3 to about 8 days is associated with a decline in subsequent litter size and farrowing rate. From about day 10 onwards, an increase in WEI is associated with an increase in these reproductive parameters. This observation agrees well with data from Clowes et al. (1994) and Vesseur (1997) who found that insemination of sows during the second estrus after weaning compared to the first one resulted in an increased pregnancy rate (+ 15 %) and subsequent litter size (+ 1.3 to 2.5 piglets). Therefore, it seems that some sows have a high genetic potential for reproduction which includes rapid return-to-estrus after weaning, fertility and prolificacy, whereas some other sows with delayed return-to-estrus after weaning take advantage of this delay to recover from the negative effects of factors acting during lactation, especially the nutritional deficit. An important question is to determine whether the WEI related variations in fertility and prolificacy are due to effects on ovulation rate, fertilization rate and/or embryo survival rate? Ovulation rate Little is known about variation in ovulation rate in association with variation in WEI. Data from three experiments with more than 350 multiparous sows (Soede et al., 1995a, b; Steverink et al., 1997) show an average ovulation rate of 21.6, 21.4, 20.5 and 19.5 at days 3 to 6 after weaning, respectively (significant linear decrease). Recently, Patterson et al. (2001) also found a negative correlation between WEI (varying between 3.0 and 5.3 days) and ovulation rate (varying between 13 and 31) in multiparous sows (r = -0.54). In contrast, in primiparous sows, Van den Brand and Langendijk (unpublished results) did not find a relation between

Total born

100 90 80 70

13 12,5 12 11,5 11 10,5 10 9,5 9

60 50 40 30 0

5

10

15

20

Total born

Farrowing rate

Farrowing rate

25

Weanin g to service interval in days (1-30)

Figure 15.4. Association of Weaning-to-estrus interval (WEI) with subsequent farrowing rate and litter size (based on Leman, 1990).

406

Weaning the pig


the weaning-to-ovulation interval (varying between 4.6 and 8.9 days) and ovulation rate (varying between 12 and 30), but they did find a relation with embryo survival (Table 15.6). Although ovulation rate is normally quite high and not the first limiting factor for litter size and farrowing rate, a role of the decrease in ovulation rate can not be ruled out, especially if the decline in number of ovulations is associated with a reduced quality of the corpora lutea, as has been suggested (Zak et al., 1997b; Almeida et al., 2000). In these sows with a short WEI, ovulation rate is probably closely related to the number of selectable follicles present at weaning.

Table 15.6. Reproductive characteristics of primiparous sows with variable weaningto-ovulation intervals (ovulation was assessed at 8-hour intervals) (Van den Brand and Langendijk, unpublished results). Weaning-to-ovulation interval (hours)

Pregnancy rate at day 35 (%) Ovulation rate Normal of embryos at day 35 Embryo survival at day 35 (%) 1 Luteal weight (g) Number of sows

110 - 145

150 - 158

166 - 214

91 19.7 ± 4.0 13.1 ± 3.1 67 ± 12 7.0 ± 1.2 23

96 19.0 ± 4.5 11.7 ± 3.7 62 ± 18 6.1 ± 1.1 26

86 19.9 ± 3.5 11.4 ± 3.2 57 ± 14 6.5 ± 1.1 29

1

Correlation between weaning-to-ovulation interval and embryo survival rate: r = -0.26, P < 0.05

For sows with a WEI of more than 10 days, it is not clear if the increase in reproductive performance is associated with an increased ovulation rate. However, an extended WEI which resulted from a three day treatment with altrenogest from weaning onwards, also resulted in an increase in ovulation rate (Koutsotheodoros et al., 1998). Fertilization rate In sows, fertilization results are very much dependent on the interval between insemination and ovulation (Waberski et al., 1994; Soede et al., 1995a), subsequently affecting litter size and farrowing rate (Nissen et al., 1997; Terqui et al., 2000). Kemp and Soede (1996) showed that, if sows with a WEI varying between 3 and 7 days were inseminated at an optimal time relative to ovulation (in the period of 24 hours before ovulation), fertilization results were not affected by WEI. In many experimental data, an increase in WEI (between 3 and 6 days) has found to be associated with a decrease in the duration of estrus and, consequently, a shorter


407


interval between onset of estrus and ovulation (review: Soede and Kemp, 1997). A similar relation between WEI and estrus duration was found on farms (Steverink et al., 1999). If the insemination strategy on farms is not adjusted to WEI, the number of sows in which the first insemination takes place after ovulation will be increased in sows with a longer WEI and hence the risk of a low fertilization rate (review: Kemp and Soede, 1997). It is not clear to what extent these phenomena are responsible for the reduction in farrowing rate and litter size as found for sows with a WEI from 3 up to 8-10 days. For sows with a WEI of more than 10 days, the duration of estrus remains as short as found for sows with a WEI of 6 days and beyond (Steverink et al., 1999). It therefore does not seem likely that the increase in reproductive performance found for these sows is associated with a better timing of insemination and therefore with higher fertilization rates. Embryonic mortality No clear information is available for the relationship between the weaning-to-estrus interval and the subsequent embryo survival. However, Van den Brand and Langendijk (unpublished results) found that, in primiparous sows, an increase in the weaning-to-ovulation interval was indeed associated with a decrease in subsequent embryo survival (Table 15.6). In these sows, ovulation rate was not associated with the weaning-to-ovulation interval. There is some circumstantial evidence suggesting that WEI is associated with subsequent embryo survival, based on experiments in which feed restriction during lactation results not only in an increase in WEI, but also in a decrease in embryo survival (Table 15.3). However, as discussed earlier (see 15.4.2.1.), this association does not seem to be very strong and it is not clear which factors are of influence. In summary, associations between WEI and subsequent reproductive performance (both farrowing rate and litter size) seem to be a combined result of effects on ovulation rate, fertilization rate and embryo survival. The relative importance of these effects is not known.

15.5

Conclusion

During lactation, suckling-neuroendocrine reflexes are the main factors inhibiting LH secretion and ovarian activity. Negative metabolic state due to high milk production creates a hormonal milieu, which may have additional inhibitory effects. In commercial farms, the timing of weaning is the decision of the producer. It generally occurs when milk production is still very high and is not progressive as in “natural” conditions. As a consequence, weaned sows are submitted to rapid changes in the nutritional balance and the hormonal secretions that generally induce estrus behavior and ovulation some days later. Internal (i.e. genetic factors, parity, body reserves) and environmental factors (i.e. light, ambient temperature, housing)

408

Weaning the pig


may influence the nature and the amplitude of these changes as well as the ability of the ovaries to respond to these changes. Therefore, both factors acting during lactation and after weaning may influence reproductive performance of weaned sows. Evidence from this review suggest that reproductive problems of sows, especially primiparous sows, are related for a large part to lactational events and less to post-weaning events. In order to improve reproductive performance and longevity, lactational sources of inhibition should be decreased, especially in first and-second litter sows. This can be done by reducing suckling stimulation and/or nutritional deficit (e.g. split-weaning, interruped suckling). Moreover, short lactations (< 21 days) should be avoided in order to allow the gonadotropic axis and the uterus to recover from the previous gestation and farrowing.

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Conclusions The chapters in this book have presented the most up-to-date information, data and background philosophy related to the various events associated with ‘weaning’. Weaning is a stressful period for both the young pig and the sow, and the act of ‘weaning’ is an unusual event in the pig production cycle because of the many changes that are simultaneously imposed on the system, eg, change of nutrition, change of environment, change of social structure, and so on. Consequently, the risks to the producer of decreased production, increased mortality and morbidity, and deteriorated health status are high at weaning, and careful management is required to ameliorate the weaning process so that any losses associated with weaning are minimized. The large array of influences can cause enormous variation in the response of piglets to the transition from the sow to the next phase. This can cause big differences in development between animals, both within and between litters. The chapters give insight how this occurs, and offer ways to avoid the negative effects of weaning A recent comment in the magazine ‘Pig International’ stated that pork remains the most consumed meat in Europe, with an average of 43.7 kg per head eaten in 2002. This compares to 23 kg for poultry and 19.4 kg for beef/veal. To maintain, and increase, this level of consumption requires due diligence to all aspects of the pig production and the supply chain, as well as improving practices and adopting new technologies to achieve higher levels of production and consumption. Weaning is an integral component of the overall pig production cycle, predominately because of the impact weaning weight and post-weaning performance can have on finisher pig performance and profitability. Fertility of the weaned sow is also an important determinant of profitability in the system. However, new challenges are continually being faced by the pig Industry, such as the increasing awareness of society with respect to animal welfare, food safety, the environment, and the ‘quality’ of production, especially with respect to antibiotics and some minerals as growth promoters. Many of these challenges concern weaning and, on balance, the process of ‘weaning’ and its effects has never been considered more important. To this end, we believe that the material contained within “Weaning the Pig: Concepts and Consequences”, is both timely and pertinent to many of the issues being faced around the world today regarding weaning. We trust that you have enjoyed the chapters in this book and believe that the diversity of topics covered, including the fate of the weaned sow, will assist with your business or line of expertise in the pig Industry. John Pluske Jean Le Dividich Martin Verstegen


421

List of authors A.C. Beynen, Department of Nutrition, Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80152, 3508 TD Utrecht, The Netherlands P.H. Brooks, University of Plymouth, Faculty of Land, Food and Leisure, Seale-Hayne Campus, Newton Abbot, Devon, TQ12 6NQ, United Kingdom D. Burrin, USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030, USA S.S. Dritz, Department of Animal Sciences and Industry, Kansas State University, Manhattan KS 66506-0201, USA F.R. Dunshea, Natural Resources and Environment, Sneydes Road, Werribee Victoria 3030, Australia R.D. Goodband, Department of Animal Sciences and Industry, Kansas State University, Manhattan KS 66506-0201, USA D.J. Hampson, School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia. M. Hay, Ecole Nationale Vétérinaire de Toulouse, 23 Chemin des Capelles, 31076 Toulouse, France D.E. Hopwood, Animal Resources Centre, Murdoch Drive, Murdoch, WA 6150, Australia D. Kelly, Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen, AB2 9SB, Scotland B. Kemp, Animal Husbandry Group, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands M.R. King, Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11-222, Palmerston North, New Zealand R.H. King, Agriculture Victoria, Sneydes Road, Werribee Victoria 3030, Australia J. Le Dividich, INRA-UMRVP, 35590 St-Gilles, France F. Madec, Agence Française de Sécurité Sanitaire des Aliments, BP 53, Zoopôle Les Croix, 22440 Ploufragan, France G.P. Martineau, Ecole Nationale Vétérinaire de Toulouse, 31076 Toulouse, France

422

Weaning the pig

H.M. Miller, The , Centre for Animal Sciences, LIBA, School of Biology, Leeds LS2 9JT, United Kingdom P.C.H. Morel, Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11-222, Palmerston North, New Zealand P. Mormède, Neurogénétique et Stress, INSERM U471, INRA, Université Victor Segalen Bordeaux 2, Institut François Magendie, 33077 Bordeaux, France J.L. Nelssen, Department of Animal Sciences and Industry, Kansas State University, Manhattan KS 66506-0201, USA P. Orgeur, INRA- PRMD, 37380 Tours, France J.R. Pluske, School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch WA 6150, Australia A. Prunier, INRA, Unite Mixte de Recherches sur le Veau et le Porc, Saint-Gilles, France H. Quesnel, INRA, Unite Mixte de Recherches sur le Veau et le Porc, Saint-Gilles, France R.D. Slade, The , Centre for Animal Sciences, LIBA, School of Biology, Leeds LS2 9JT, United Kingdom N.M. Soede, Animal Husbandry Group, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands B. Stoll, USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030, USA M.D. Tokach, Department of Animal Sciences and Industry, Kansas State University, Manhattan KS 66506-0201, USA C.A.Tsourgiannis, University of Plymouth, Faculty of Land, Food and Leisure, SealeHayne Campus, Newton Abbot, Devon, TQ12 6NQ, United Kingdom M.A.M. Vente-Spreeuwenberg, Nutreco Swine Research Centre, P.O. Box 240, 5830 AE Boxmeer, The Netherlands M.W.A. Verstegen, Animal Nutrition Group, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands I.H. Williams, School of Animal Biology, Faculty of Natural and Agricultural Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia


423

Index A

B

α-linolenic acid 175 accumulate body fat 31 active immunity 220, 224 active or passive coping strategy 89 acute IGF-I treatment 71 acute phase protein production 150 ad libitum 25 adaptations to underfeeding 70 adaptive immunity 221 adrenal reactivity to ACTH 54 affinity constants 128 aggressive behaviours 57 AIAO see all-in / all out (AIAO) air velocity 343 all-in / all out (AIAO) 349, 353, 373-374, 377 ambient temperature 338-340, 353 amino acid transport 128 amino acid utilization 314 ammonia 167 amylase 124 amylolytic activity 40 anestrus 385-388, 397 anorexia 204, 237 anterior teats 84 antigen-presenting cell (APC) 222, 225-231, 236 antigenic compounds 43 antimicrobials 322-323 APC see antigen-presenting cell (APC) apical 127 arginine 319, 320-321 aromatic compounds 45 arterial nutrient utilization 308 aspartate 167, 311-312 ATP levels in jejunal mucosa 159

bacterial translocation 180, 184 bedding 341-342 belly-nosing 57 biochemistry of the gut 82 birth-weight 20, 25, 91, 363-364, 366-367, 371 blood plasma 56 boar 405 body – lipid 66 – protein 68 – stores 399-401 – thermal insulation 338-339 butyric acid 181, 314


C calcium 269, 274 carbohydrase induction 127 carboxymethylcellulose (CMC) 207 carnitine 269, 274 catecholamine excretion 54 CD4+ T cells 150 CD8+ T cells 134 cell proliferation 303, 305-306, 320 cellular immunity 230 cereals, cooked 43 cereals, flaked 43 CF see continuous flow (CF) changing light patterns 63 chymotrypsin 124 circulating cortisol 54 circulating free fatty acid levels 54 citrulline 312 climatic environment 404 CMC see carboxymethylcellulose (CMC) cold stress 73 colonocytes 181 colostrum 362, 368-369, 371 commercial

425

Index

– pellets 64 – weaning 138 – weaning age 123 compensatory growth 25 complex carbohydrates 40 concanavalin A 172 confinement-reared piglet 94 conserve gut 68 conserve protein 67 continuity of food intake 99 continuous flow (CF) 373-374 copper 269-271, 274, 288 corn starch 184 cortisol insensitivity 131 cortisol release 132 creep feed 21 creep feed consumption 42, 61, 88 creep feeding 91 cross nursing 369 crypt depth 19, 124, 125 crypt enterocytes 310 culling 385, 387 cysteine 265, 275, 316-317 cytokines 220-221, 224, 226-228, 230, 234, 237, 241, 244, 304, 322 cytosolic dipeptidase 183

D daily fluid intake 102 diarrhoea 146, 199, 201, 203, 205-208, 210, 337, 349, 351, 353, 372 diet – complexity 262-263 – formulation 259, 270, 287 – low-quality 56 dietary antigen 241 dietary interventions 41 different chain-length fatty acids 130 digestive – enzymes 43 – physiology 117, 301 – problems 54 dipeptides 168

426

dominant pigs 95 draughts 345, 350 dried porcine solubles 278 dried skim milk 277 dry pelleted feed 56

E early weaning 28, 372 easily digestible diet 56 ecophysiology 102 effects of gender 43 EGF see epidermal growth factor (EGF) elastase I 124 elastase II 124 embryo survival 385, 393-397, 400, 404, 408 endocrine changes 61 endotoxicosis 168 energy 264, 289, 368-369, 391 – deficit 65 – sources 264, 272, 285 enteral nutrition 132 enteric disease 199, 201, 211, 339, 349, 351 enterocyte 127, 184, 310 – aldohexose transporters 127 – differentiation 151 – migration distance 125 enteropathogenic E. coli 203 enterotoxigenic 202 enterotoxigenic E. coli 202, 204 enterotoxins 203, 205, 207, 210, 224 enzyme activities 119 epidermal growth factor (EGF) 182 epithelial barrier 99, 237, 238 epithelial integrity 134 epithelial lining of the gut 99 Escherichia coli 199-204, 206, 210-211 essential amino acids 133 estradiol-17β 389, 393 estrus 385, 388, 393-396, 398, 404-405, 408 ETEC 202, 204-205, 208-210 exogenous catecholamine 73

Weaning the pig

Index

F family affiliations 85 farrowing rate 394, 398, 405-408 fasting heat 26 fat 273-274, 286-288, 399, 400 – reserves 65, 70 – supplementation 172 fatness 400-401 feed – flavour 45 – intake pattern 396 – preferences 45 feeder 289, 337, 346, 354 feeding – activity 88 – behaviour 47, 81 – patterns 101 – spaces 47, 90 – strategy 368, 370 – systems 42 fermentation 199, 200, 205, 207, 209 fermented liquid feed 56 fertility 394, 406 fertilization rate 394, 404, 407-408 fetal gluconeogenic capacity 73 fetal villus enterocyte 120 fibre 205-206, 210-211 fish meal 56, 276-277, 284, 286-288 flooring material 337, 346, 354 follicle 389-390, 392-397, 407 foraging behaviour 85 fostering 362, 368-369, 372 fresh liquid feed 56 FSH 390, 392-393 functional feed ingredients 145, 185

G galactose 127 GALT 225 gastric development 118 gastric motility 139 gastrointestinal – hormones 152


– tract 40 – trauma 183 genotypes, modern 66 GLP-1 135, 137 GLP-2 135, 137, 305-306, 310 glucagon-like peptide 2 (GLP-2) 135, 137, 305-306, 310 glucoamylase 127, 151 glucocorticoid receptor levels 54 glucocorticoid receptors 132 gluconeogenesis 66, 72 glucose 127, 312, 313 glutamate 167, 308-309, 311-313, 319-320 glutamine 167, 308-309, 31-313, 319-321 glutamine administration 168 glutathione 167 glycerol, mobilised 67 glycogen breakdown 66 goblet cells 133, 149 Gompertz function 18 grain sources 275, 285 group size 337, 348, 354 growth – factors 130 – potential 17, 365, 371, 376 – rates of organs 123 – to slaughter 20 gruel 22 gut – development 39 – ecosystem 82 – metabolism 307 – physiology 117, 301

H haemolytic E. coli 202, 207, 210-211 haemolytic ETEC 203-204, 206-210 health 353, 361, 373 hepatic ST receptor mRNA 70 high ambient temperature 344, 405 highly palatable 56 homeorhesis 67 homeostatsis 103

427

Index

housing system 337, 405 HPA see hypothalamic-pituitary-adrenal (HPA) axis humoral immunity 221-222 hydrolase activities 122 hygiene 351, 353-354 hypersensitivity 133, 230, 241-244, 279-280, 286 hypothalamic-pituitary axis 72 hypothalamic-pituitary-adrenal (HPA) axis 54 hypothalamic-pituitary-ovarian axis 392, 405

I IgA 223-224, 226 – cells 232 IGF-I 69, 391, 392 IgG 223-224, 242 IgM 223-224 – cells 232 immediate post-weaning period 63 immune system 44, 102, 219-224, 226, 228, 230, 233, 242, 244 immunoglobulin 29, 39, 219, 222-224, 226, 233, 368-369 immunological low point 82 inappropriate gut microflora 100 increased rate of cell loss 148 incretin hormones 135 individual variation 57 infection 322 inflammation 243-244 ingestion of amniotic fluid 119 ingredient selection 263 initial feed intake 56 innate immunity 220 insulin 69, 72, 391-392, 397, 400 insulin-like growth factors 182 interleukin-1 (Il-1) 150 interleukin-6 Il-6 150 interval between nursing events 84 intestinal

428

– absorptive capacity 128 – barrier function 147 – enlargement 122 – immune system 224, 230-231, 233, 236-237, 243 – immunity 219, 231, 233, 237, 243-244 – inflammation 220, 228 – microflora 199 – morphology 124, 234 – nutrient requirements 301 – nutrient utilization 301, 306 – permeability 149 intestine – large 200, 202, 205, 207, 211 – small 199-210 intestinotrophic events 138 intraluminal nutrients 137 intravenous infusion 68 intravenously supplied TPN 180 inverse relationship 91 isoleucine 265

K ketones 313

L L-arginine 183 lack of – enteral stimulation 152 – familiarity 96 – nutrients 155 lactation length 394, 396, 402 lactic acid 181 – bacteria 63 lactose 262-263, 272-273, 285-287 lamina propria 221, 225-228, 230-233, 236, 238-241 larger matriarchal group 85 LC-PUFA see long-chain, polyunsaturated fatty acid (LC-PUFA) LCFA see long-chain fatty acid (LCFA) LCT see lower critical temperature (LCT) lean tissue 69

Weaning the pig

Index

learning phase 85 LH 389-393, 400 lighting 344 lipase 124 lipase activity 172 liquid diets 41, 90 liquid feeding 107 litter cohesion 57 litter size 37, 362-364, 388-389, 394, 398399, 401-402, 405-407 long-chain fatty acid (LCFA) 321 long-chain, polyunsaturated fatty acid (LCPUFA) 321-322 long-term benefits 23 longevity 385, 394 lower critical temperature (LCT) 20, 339, 341-343 LR3IGF-I infusion in suckling piglets 71 luminal nutrient utilization 308 lymphocyte 147, 222, 226-230, 232-233, 236-237, 241 lysine 264-267, 278, 282, 318, 398

M M-cells 147 macrophage 220, 227, 231, 236-237 major histocompatibility complex (MHC) 222, 225-231, 236-238, 241 malnutrition 158 maltase 127, 151 – activities 40 maltose 121 management options 38 management strategies 108 maternal catabolism 392 meal or a pellet 90 mechanical stimulation 155 medicated early weaning (MEW) 374 metabolic status 391 methionine 265, 275, 278, 316-317 MEW see medicated early weaning (MEW) MHC see major histocompatibility complex (MHC)


microbial environment 82 microenvironment 341 microflora 199-201, 203, 205-206, 209 microscopic morphology 176 milk energy intake 63 milk products 273, 283, 285 minerals 269 minimising the growth check 27 mixing of animals 53-54 mobilisation of body lipid 65 monosaccharides 127 morbidity 29 mortality 29 mucin 211, 224, 306, 317 mucosal function 145 mucosal integrity 167 mucus 202, 211 muscle fibres 365

N NDO see non-digestible oligosaccharides (NDO) NEFA concentrations 66 negative protein balance 68 neonatal enteral nutrition 129 neuroendocrine changes 53, 57 non-digestible oligosaccharides (NDO) 175, 180 non-optimal indoor climate 350 non-starch polysaccharide (NSP) 206-212 norepinephrine 73 novel environment 53 noxious gases 344 NSP see non-starch polysaccharide (NSP) nucleosides 185 nucleotides 184, 322 nutritional deficit 57 nutritional management 37 nutritional program 259, 262, 288 oedema 203

429

Index

O oils 43 oligosaccharides 282-283 ontogeny of somatotropin 69 operant panels 95 oral tolerance 228-229, 243 organic acids 283 ornithine 312, 320 ovalbumin 166 ovulation 385 ovulation rate 393-398, 400-401, 406-408 oxidative fuels 311-312

P pair-feeding 160 pancreatic enzyme activities 119 Paneth cells 225 paracellular permeability 159 paracellular transport 150 passive immunity 223, 374 PDV see portal-drained visceral (PDV) pen structure 337, 346, 354 pepsin 40 peptide absorption 129 peri-natal colon 120 permeability 166 Peyer’s patches 225-226, 233 phenylalanine 318-319 phosphorus 269 photoperiod 405 phytase 283 pituitary hormones 389 plant proteins 30 plasma – catecholamine 73 – cortisol 73 – glucose 66 – glycerol concentrations 67 – IGF-I 69 – insulin 72 – ST 69 poly-unsaturated fatty acids 172 polyamines 183, 320-321

430

portal-drained visceral (PDV) 307-309, 311, 313-315, 318, 322 post-hepatic amino acid supply 72 post-weaning 92 – colibacillosis (PWC) 199, 201-212 – diarrhoea 44 – growth check 37 – growth rate 92 – intestinal maturation 122 – lean tissue deposition 70 potato protein 281 pre-natal effects 39 pre-weaning creep food intake 39-40, 43 prebiotics 181 probiotics 181-282 production cycle 37 proglucagon derived peptides 135 proinflammatory immune system components 134 prolificacy 394, 402, 406 proline 312, 319, 320 protein intake 398, 401 protein sources 30, 262-263, 275-278, 281282, 284, 287-288 putriscine dihydrochloride 183 PWC see post-weaning colibacillosis (PWC)

R rapid intestinal growth 129 rate of lipogenesis 66 reduced functionality 126 reduced welfare 57 reduction in nocturnal temperature (RNT) 341-342 relative humidity 343 reproductive axis 385, 388-389 reproductive performance 385, 394, 396, 398, 400-401, 408 restricted feeding 44, 160 retrograded starch 176 ribosylphosphates 184 rice 206, 209-211 risk factors 351, 353-354

Weaning the pig

Index

RNT see reduction in nocturnal temperature (RNT)

S salmonellosis 202 satiety 103 SCFA see short-chain fatty acids (SCFA) secretory IgA 226, 227 secretory immunoglobulins 147 segregation 374, 377 serotype 203, 207 SEW 53, 275, 280, 283-288, 375 sexual dimorphism 43 short-chain fatty acids (SCFA) 180, 305-306, 310, 313-314 sigmoidal growth 18 similar intra-suckling intervals 84 skeletal muscle protein synthesis 72 skim milk 63, 277, 284 small intestinal histology 64 small intestinal integrity 149 social facilitation 97 social rank 89 soluble fibre 175 somatotrophic activity 70 somatotrophic axis 54 somatotropin 68 sow – genotypes 88 – milk 21, 86 – milk yield 56 – vocalisations 86 soybean meal 262, 279-281, 284, 286-287 soybean, hydrolysed 166 spermine concentration 184 split weaning 22, 368, 370 spray-dried – animal plasma 263, 269, 275, 284, 286 – blood meal 276, 278, 284, 286-288 – bovine colostrum 28, 30 – egg protein 281, 284 – wheat gluten 282


– whole egg 276 ST receptor gene 69 starch 399 starter diets 27 stimulation of food intake 28 stocking densities 347, 354 stocking rate 337 stomach mass 123 stress hormones 53 suckling 389, 402 sucrose 121 supernumerary 361, 362-363, 371, 376-377 supervision of farrowing 368 supplemental water 47 supplementary feeding 23 supplementary milk 22 supplemented piglets 24 survival 367, 376 sweetener 45, 106 synchronous feeding 97-98

T T cells 222 taxation of the adaptive mechanisms 57 temperature fluctuation 342, 344-345, 350 thermal requirement 337-339 thermoregulation 39 threonine 265, 316-318, 320-321, 323 tight junctions 182, 224, 239 tissue thermal insulation 353 TNF see tumor necrosis factor (TNF) total heat production 65 trace minerals 269, 271 transient starvation 100 transportation 53 true digestibilities 19 trypsin 124 tryptophan 265 tumor necrosis factor (TNF) 150 tyrosine 319

431

Index

U underfed piglet 47 underfeeding 185 undernutrition 67 underprivileged 361-362, 365-367, 371, 376 urinary excretion 53 urinary norepinephrine 73

whole-body fractional protein 67 withholding soybean meal 44

Z zinc 269, 271 – oxide 270-271, 285-288

V valine 265 ventilation 343-344, 351 VFA see volatile fatty acids (VFA) villous architecture 19, 100, 120, 126, 147 villus enterocytes 310 villus surface 138 viscosity 208-209 vitamins 268-269 volatile fatty acids (VFA) 205 volumetric fill 104

W ω-3 polyunsaturated 175 ω-6 polyunsaturated 175 water – availability 47 – intake 47, 87 – temperature 105 – holding capacity 208, 210 waterer 337, 346, 354 weaning – age 28, 37, 259-261 – anorexia 54 – of piglets 149 – weight 260, 364, 366 – weight advantage 38 – elicited gut hormone secretion 135 – induced impairment 145 – to-estrus interval (WEI) 385, 393-395, 397-398, 400-402, 405-408 WEI see weaning-to-estrus interval (WEI) weight of the small intestine 64 whey 272, 276-278, 284, 286-288 – protein 166

432

Weaning the pig

Weaning The Pig: Concepts and Consequences

The Baby-Led Weaning Cookbook

Pig

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The House and The Pig

The Sheep-Pig (Babe)

The Steam Pig

Pig Island

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Perfecting the Pig Environment

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Interstellar Pig

Pig Island

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The Genetics of the Pig

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Interstellar Pig

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