Nitrogen and Phosphorus Nutrition of Cattle

Nitrogen and Phosphorus Nutrition of Cattle Reducing the Environmental Impact of Cattle Operations

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Nitrogen and Phosphorus Nutrition of Cattle Reducing the Environmental Impact of Cattle Operations

Edited by

Ernst Pfeffer Institut fu¨r Tiererna¨hrung der Universita¨t Bonn, Endenicher Allee 15, D-53115 Bonn, Germany and

Alexander N. Hristov Department of Animal & Veterinary Science, University of Idaho, PO Box 44 -2330, Moscow, ID 83844 -2330, USA

CABI Publishing

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ß CAB International 2005. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. A catalogue record for this book is available from the Library of Congress, Washington, DC, USA. Library of Congress Cataloging-in-Publication Data Nitrogen and phosphorus nutrition in cattle / edited by Alexander A. Hristov and Ernst Pfeffer. p. cm. Includes bibliographical references (p. ). ISBN 0-85199-013-4 (alk. paper) 1. Cattle--Feeding and feeds. 2. Nitrogen in animal nutrition. 3. Phosphorus in animal nutrition. I. Hristov, Alexander A. II. Pfeffer, Ernst. III. Title. SF203.N58 2005 636.2’0852--dc22 2004022637 ISBN 0 85199 013 4

Typeset by SPI Publisher Services, Pondicherry, India Printed and bound in the UK by Biddles Ltd, King’s Lynn

Contents

Contributors

vi

1

Interactions between Cattle and the Environment: a General Introduction E. Pfeffer and A.N. Hristov

2

Nitrogen Requirements of Cattle C.G. Schwab, P. Huhtanen, C.W. Hunt and T. Hvelplund

13

3

Nitrogen Metabolism in the Rumen N.D. Walker, C.J. Newbold and R.J. Wallace

71

4

Factors Affecting the Efficiency of Nitrogen Utilization in the Rumen A.N. Hristov and J.-P. Jouany

117

5

Whole-animal Nitrogen Balance in Cattle J.L. Firkins and C. Reynolds

167

6

Phosphorus Metabolism in the Rumen R.L. Kincaid and M. Rodehutscord

187

7

Phosphorus Metabolism in Ruminants and Requirements of Cattle E. Pfeffer, D.K. Beede and H. Valk

195

8

Effects of Dietary Phosphorus and Nitrogen on Cattle Reproduction J.D. Ferguson and D. Sklan

233

9

Improving the Efficiency of Nutrient Use on Cattle Operations J. Schro¨der, A. Bannink and R. Kohn

255

Index

1

281

v

Contributors

Dr Bannink, Wageningen University and Research Centre, Institute for Animal Science and Health, PO Box 65, 8200 AB Lelystad, The Netherlands. Dr Beede, Michigan State University, Department of Animal Science, 2265K Anthony Hall, East Lansing, MI 48824-1225, USA. Dr Ferguson, University of Pennsylvania, Department of Clinical Studies, New Boldon Center, 382 West Street Road, Kennett Square, PA 19348, USA. Dr Firkins, Ohio State University, Department of Animal Sciences, College of Food, Agriculture and Environmental Science, Columbus, OH 43210, USA. Dr Hristov, University of Idaho, Department of Animal and Veterinary Science, PO Box 44-2330, Moscow, ID 83844-2330, USA. Dr Huhtanen, MTT Agrifood Research Centre, Animal Production Research, FIN-31600, Jokioinen, Finland. Dr Hunt, University of Idaho, Department of Animal and Veterinary Science, PO Box 44-2330, Moscow, ID 83844-2330, USA. Dr Hvelplund, Institute of Agricultural Sciences, Department of Animal Nutrition and Physiology, PO Box 50, DK-8830 Tjele, Denmark. Dr Jouany, Institut National de la Recherche Agronomique, Centre de Clermond-Ferrand – Theix, F-63122 Saint Genes Champanelle, France. Dr Kincaid, Washington State University, Animal Sciences Department, Pullman, WA 99164-6310, USA. Dr Kohn, University of Maryland, Department of Animal and Avian Sciences, College Park, MD 20742, USA. Dr Newbold, Rowett Research Institute, Bucksburn, Aberdeen, AB21 9SB, UK. Professor Pfeffer, Institut fu¨r Tiererna¨hrung der Universita¨t Bonn, Endenicher Allee 15, D-53115 Bonn, Germany. Dr Reynolds, College of Food, Agriculture and Environmental Sciences, Wooster, OH 44691, USA. Dr Rodehutscord, Martin-Luther-Universitat Halle-Wittenberg, Institut fur Ernahrungswissenschaften, D-06108 Halle (Saale), Germany. Dr Schro¨der, Plant Research International, Wageningen University and Research Centre, PO Box 16, 6700 AA Wageningen, The Netherlands. Dr Schwab, University of New Hampshire, Department of Animal and Nutrition Sciences, Ritzman Lab, 22 Colovos Road, Durham, NH 03824, USA. vi

Contributors

vii

Dr Sklan, Hebrew University, Faculty of Agriculture, PO Box 12, Rehovot 76-100, Israel. Dr Valk, Animal Sciences Group, Edelhertweg 15, PO Box 65, NL 8233 AB Lelystad, The Netherlands. Dr Walker, Rowett Research Institute, Bucksburn, Aberdeen, AB21 9SB, UK. Dr Wallace, Rowett Research Institute, Bucksburn, Aberdeen, AB21 9SB, UK.

Preface

Animals depend on regular supply of a number of nutrients serving different functions in their metabolism. These nutrients have to be provided by feeds ingested by the animals. Normally, nutrients yielding metabolizable energy are responsible for most of the feed cost. For this reason it appeared logical for a long time to aim at maximum efficient utilization of feed energy as the target of calculating rations for farm animals, while more or less generous ‘safety margins’ were recommended with respect to less expensive nutrients by advisors in all countries until recently. This purely economical approach of optimizing rations did not take into consideration the fate of that part of ingested nutrients which is not transferred into the animal products. Only towards the end of the 20th century was it generally recognized that animal units may be the cause of dramatic local or regional surpluses of nutrients creating serious impacts on soil, water and air. Limiting nitrate in drinking water to lowered concentrations after changed legislation appeared especially critical from groundwater found in regions with high stocking densities of farm animals and it was estimated that dairy cows were responsible for more than half of the ammonia emitted into the air, consequently causing accumulations of nitrogenous compounds in natural precipitation. Even after removal of phosphates from detergents intensive growth of algae was observed in lakes and streams and this was interpreted to a great proportion as a consequence of phosphate enrichment in particulate matter transferred from fields into surface water due to erosion. Again, the highest phosphate concentrations of soils were found in regions with very high stocking densities. Animal nutritionists increasingly realized that this situation is to be seen as a challenge to their scientific discipline. Avoiding nutrient deficiencies by allowing unnecessary safety additions may ignore the ecological demand that production of food for humans has to be sustainable. A great number of studies dealing with details of sustainable animal production has been carried out and published and any attempt to survey the present state of the art has to be restricted with respect to species as well as nutrients. This book, therefore, is restricted to nitrogen and phosphorus in cattle, from basic biological facts to practical feeding and farm management. The editors are grateful to all authors for their respective contributions and to CABI for publishing this book. In September 2004 we received the sad news of the death of David Sklan, he will be remembered as a respected scientist and a dear colleague. Ernst Pfeffer and Alex Hristov Bonn, Germany, and Moscow, Idaho, October 2004.

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Abbreviations

Chapter 1: AFO CAA CAFO CWA DM ELG EPA NMP NPDES NPN PMx TMR VAPS VOC

Animal feeding operation Clean Air Act Concentrated animal feeding operation Clean Water Act Dry matter Effluent limitations guidelines Environmental Protection Agency Nutrient management plan Nutrient pollution discharge elimination system Non-protein nitrogen Particulate matter (equivalent diameters less than
mm) Total mixed ration Voluntary alternative performance standards Volatile organic compounds

Chapter 2: AA AAT ADG ADIN ATP BW CNCPS CP dCHO DIM DIP DK DM

Amino acids Amino acids absorbed from the small intestine Average daily gain Acid detergent insoluble nitrogen Adenosine tri-phosphate Body weight Cornell Net Carbohydrate and Protein System Crude protein Intake of digestible carbohydrates Days in milk Digestible intake protein Danish system of protein evaluation Dry matter

ix

x

DMI DOM DUP DVE EAA ECM ECP EDP EE EDP EPD EQSBW ERDP FIN FME FOM GER His INRA L Leu Lys MCP Met MP MPY MSPE MUN NDF NAN NE NPN NRC NSC nXP OM PBV PDIA PDIE PDIN QDP RDP RE RMSE RUP SDP TDN Thr TP VAL VFA WG

Abbreviations

Dry matter intake Digestible organic matter Digestible undegraded protein Darm Verteerbar Eiwit Essential amino acids Energy corrected milk Endogenous crude protein Effective protein degradability Ether extract Effective degradability of protein Effective protein degradability Equivalent shrunk body weight Effective rumen degradable protein Finnish system of protein evaluation Fermentable metabolizable energy Fermentable organic matter German system of protein evaluation Histidine Institut Nationale de la Recherche Agronomique Leeding of feeding (multiple of maintenance) Leucine Lysine Microbial crude protein Methionine Metabolizable protein Milk protein yield Mean squared prediction error Milk urea nitrogen Neutral detergent fibre Non-ammonia nitrogen Net energy Non-protein nitrogen National Research Council Non-structural carbohydrates Utilizable crude protein Organic matter Protein balance value in the rumen Truly digestible rumen undegraded protein Protein value, when energy is limiting microbial growth Protein value, when nitrogen is limiting microbial growth Quickly degraded protein Rumen degradable feed protein Retained energy Root mean square error Rumen undegradable feed protein Slowly degraded protein Total digestible nutrients Threonine Tissue protein Valine Volatile fatty acids Weight gain

Abbreviations

Chapter 3: AA Ala Arg ATP BAC CFB CP CPCR DCCD DIC DM DNA DPP EDTA GDH GIT Gly GM HAP Leu LPNA Lys LysAlaMNA mRNA NAD NADP NSAAPPPNA PCR Pro RDP RDNA RNA scFA SDS-PAGE TCA

Amino acids Alanine Arginine Adenosine tri-phosphate Bacterial artificial chromosome Cytophaga-flexibacter-bacteroides Crude protein Competitive polymerase chain reaction Dicyclohexylcarbodiimide Diphenyliodonium chloride Dry matter Deoxy ribonucleic acid Dipeptide peptidase Ethylene diamine tetraacetic acid Glutamate dehydrogenase Gastro-intestinal tract Glycine Genetically modified Ammonia hyperproducing bacteria Leucine Leucine p-nitroanilide Lysine Lysine alanine 4-methoxy-2-nitroanilide Messenger ribonucleic acids Nicotinamide adenosine dinucleotide Nicotinamide adenosine dinucleotide phosphate N-Succinyl alanine alanine phenylalanine proline p-nitroanilide Polymerase chain reaction Proline Rumen degradable protein Ribosomal deoxy ribonucleic acid Ribonucleic acids Short chain fatty acids Sodium dodecyl sulphate polyacrylamide gel electrophoresis Tri-carboxylic acid

Chapter 4: ATP BCFA BW CHO CP CT DM DMI EO ESBM FA

Adenosine tri-phosphate Branched chain fatty acids Body weight Carbohydrates Crude protein Condensed tannins Dry matter Dry matter intake Essential oils Expeller soybean meal Fatty acid

xi

xii

GLU HMEC HT MN MPS MUN NAN NDF NE NFC NPN NSC OM PUN RDP RUP rusitec SSBM STA TNC VFA WSC

Abbreviations

Corn dextrose High moisture ear maize Hydrolysable tannins Microbial nitrogen Microbial protein synthesis Milk urea nitrogen Non-ammonia nitrogen Neutral detergent fibre Net energy Non-fibre-carbohydrates Non-protein nitrogen Non-structural carbohydrates Organic matter Plasma urea nitrogen Ruminally degradable dietary protein Ruminally undegradable protein Rumen simulation technique Solvent soybean meal Corn starch Total non-structural carbohydrates Volatile fatty acids Water soluble carbohydrates

Chapter 5: ATP BUN CP DM DMI MRNA NAD NAN NANMN NEL NPN PDV RDP RNA RUP TDN

Adenosine tri-phosphate Blood urea nitrogen Crude protein Dry matter Dry matter intake Messenger ribonucleic acid Niacin adenosine dinucleotide Non-ammonia nitrogen Non-ammonia non-microbial nitrogen Net energy for lactation Non-protein nitrogen Portal drained viscera Rumen degradable protein Ribonucleic acids Rumen undegradable protein Total digestible nutrients

Chapter 6: ADG ATP FTU Pi

Average daily gain Adenosine tri-phosphate Unit of phytase activity Inorganic phosphate

Abbreviations

Chapter 7: CP DipM DM DMI Pi PTH SA

Crude protein Disintegrations per minute Dry matter Dry matter intake Inorganic phosphate Parathyroid hormone Specific radioactivity

Chapter 8: ATP cAMP CL CP CR DIPR DM DMI DNA LH LR MP MUN Pi RDN RUP SPC TDN

Adenosine tri-phosphate Cytosolic adenosine monophosphate Corpora lutea Crude protein Conception rate Difference between requirement for and dietary supply of rumen degradable protein Dry matter Dry matter intake Deoxy ribonucleic acids Luteinizing hormone Likelihood Ratio Metabolizable protein Milk urea nitrogen Inorganic phosphate Rumen degradable protein Rumen undegradable protein Services per conception Total digestible nutrients

Chapter 9: A AN ANU CP CF DM EX F FP I IM IMN IMNU IMP

Milk and meat Additional nitrogen requirement Additional nitrogen requirement per unit milk and/or meat Crude protein Nutrients of crops appearing as feed Dry matter Fraction of harvested nutrients being exported Feed and bedding Transfer of nutrients from feed to product (efficiency of nutrient utilization) Nutrient input Fraction of nutrients in feed and bedding material being imported Permitted feed nitrogen import per hectare Permitted feed nitrogen imported per unit milk and/or meat Permitted feed phosphorus import per hectare

xiii

xiv

IMPU L M MACN MAON MP MS O RDP SC

Abbreviations

Permitted feed phosphorus imported per unit milk and/or meat Nutrient losses Loss in faeces, urine and worn bedding Maximum attainable crop nitrogen per hectare Maximum attainable nitrogen output per hectare Metabolizable protein Transfer of manure nutrients to soil Nutrient output Rumen degradable protein Transfer of nutrients from soil to harvested crops

1

Interactions between Cattle and the Environment: a General Introduction

1 2

E. Pfeffer1 and A.N. Hristov2

Institut fu¨r Tiererna¨hrung der Universita¨t Bonn, Bonn, Germany Department of Animal and Veterinary Science, University of Idaho, Moscow, Idaho, USA

1.1 1.2

Role of Animals in Man’s Search for Food ....................................................... 1 Historical Highlights in Research Concerning N and P as Nutrients .............................................................................................. 2 1.3 Resources of N and Phosphate as Plant Nutrients ............................................ 4 1.4 Elementary Balances in Animal Production ..................................................... 6 1.5 Environmental Regulations in the USA and the European Union ........................ 7 References ........................................................................................................ 10

1.1

Role of Animals in Man’s Search for Food

At the beginning of human civilization, hunting animals was the predominant way to find food for man in most parts of the world. Domestication of animals was a remarkable step to secure food when, as a consequence of the growing density of human population, natural resources limited the potential quantity of food to be found just by hunting. Developing pastoral systems were characterized by large areas producing little or no crops that could be consumed directly by man. Most of the vegetation growing on these areas could be utilized only as feed for the herds, mostly consisting of ruminants. Regular bleeding of animals and using the blood as food, from time to time slaughtering individual animals from the flock and finally allowing the offspring to drink only a part of the milk produced by their dams, in order to use the remaining milk as food for human consumption, were phases of developing more intensive forms of animal husbandry.

Each of these phases ranging from nomadic systems to intensive grassland management can still be found in some regions of the world. The major function of animals in these systems is to extract nutrients from vast areas and concentrate them into food for man. In this phase excreta of the animals usually raise hardly any interest in herdsmen. In order to increase the amount of food harvested per unit of area, land was ploughed and crop production was started in areas where climate and access to water allowed this. Density of human population usually is much higher in these crop-producing than in pastoral systems, i.e. land often is limiting the potential amount of food produced. Animals in such systems have the function to increase yields per unit of area and this is achieved by using them as draught animals and by using their excreta as fertilizer on the fields. The old German expression of ‘pasture as the mother of arable land’ illustrates this situation: draught animals and animals grazing on extensive rangeland during the daytime were flocked or kept in stalls overnight; excreta voided during

ßCAB International 2005. Nitrogen and Phosphorus Nutrition of Cattle (eds E. Pfeffer and A.N. Hristov)

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E. Pfeffer and A.N. Hristov

the night were conserved and used to increase the concentration of plant nutrients in the soil of tilled fields. The author of the first German textbook of agricultural science expressed his opinion about the function of animals in farms as follows: Die Tiere sind bloß wie Maschinen anzusehen, welche . . . die Fu¨tterung zum . . . bei weitem gro¨ßern Theil . . . in Mist . . . verwandeln (The animals are to be regarded just like machines which to by far the greater part convert feed into manure) (Thaer, 1809, p. 257).

Although plant nutrients were not yet identified, it was recognized that without returning excreta of animals as manure fertility of the fields could not be sustained. Today, in most areas farmers and extension workers no longer regard manure as the only source of plant nutrients, but ‘cut and carry’ systems in some areas seem to still follow this line. As long as farmers do not purchase fertilizer or feeds they are in danger of having negative nutrient balances in their fields, and for this reason excreta of animals are regarded as a saving box for plant nutrients which have to be returned to the land from which they were originally extracted and transferred into plant material. Up to a certain degree, therefore, ‘horizontal movement of nutrients’ can be an intended effect of animal husbandry by which animals carry nutrients from wide areas into folds or stalls, where their excreta are regarded as a major product of high value. More than a 100 years after Albrecht Thaer, Theodor Brinkmann, professor of farm management in Bonn, tried to determine the value of the various production factors for the farmer. Although he no longer regarded excreta as the main animal product, he pointed out that purchased concentrate feeds not only promoted milk and meat production directly but also imported plant nutrients into the farm. The monetary value of these plant nutrients had to be taken into account; he critically added that this, however, was valid only as long as the respective plant nutrients were truly missing in the farm because otherwise purchased feeds would only increase existing surpluses (Brinkmann, 1922, p. 109). This latter situation of excessive presence of nutrients has developed towards the end of the 20th century in wide regions of Europe and North America with the consequence of negative ecological effects. A first attempt to create a comprehensive international overview on

emission of ammonia was made more than 10 years ago (Klaassen, 1992) and feeding strategies to decrease potentials for nitrogen (N) and phosphorus (P) pollution have gained increasing relevance (CAST, 2002). This book intends to summarize scientific aspects related to nitrogen and phosphorus supply and use by cattle and resulting impacts on sustainability of agriculture. The restriction to N and P appears justified at present as these nutrients have been found to play a predominant role in the fertility of soils and in impacts on the environment, but other elements will have to be taken into consideration as well in the near future.

1.2 Historical Highlights in Research Concerning N and P as Nutrients Of the more than 100 elements found in the periodic table today, only a dozen were known 350 years ago, among them carbon, sulphur, iron, copper, silver and gold. The term ‘element’ was not used in today’s meaning and alchemists were convinced that they could, by experimentation, find the ‘philosopher’s stone’ by which they could turn worthless materials into gold. One of these alchemists was Henning Brand in Hamburg who in 1669 heated concentrated urine without admitting air and found a snow-white substance, which immediately burned out when exposed to air, thereby illuminating the dark room (Childs, 2003; Van der Krogt, 2003d). This property of giving light was the base for naming of the substance discovered by Brand, from the Greek words wvs [phos] ¼ light; and werv [phero] ¼ to carry, to bring. Phosphorus thereby was the first element to be identified in modern times. About 100 years after Brand’s discovery, the Swedish chemists Gahn and Scheele found calcium phosphate to be a major constituent of bone (McDowell, 1992). Today it is common knowledge that P is involved in practically all meta2 bolic processes as phosphate (H2 PO 4 =HPO4 ) or as phosphate-containing organic compounds. About a century after the finding of P, the identification of three gases substantially promoted the scientific understanding of nature (Van der Krogt, 2003a,b,c): 1. In 1766, Henry Cavendish reported to the Royal Society in England about ‘inflammable air from the metals’.

Interactions between Cattle and the Environment

2. In 1772, Daniel Rutherford in Scotland showed that air in which animals had breathed (even after removal of the exhaled ‘fixed air’ – carbon dioxide) was no longer able to burn a candle, he named this entity ‘aer malignus’ or noxious air. 3. In 1774, Joseph Priestly obtained a colourless gas by heating red mercuric oxide in which a candle would burn ‘with a remarkable flame’ (Carl Wilhelm Scheele in Sweden had discovered the same gas in 1766, but his publication was delayed until 1777, due to neglect by his publisher). Antoine Lavoisier (1743–1794) suggested names for these gases derived from Greek. They include the syllable ‘ge`ne’ from geinomai (geinomai) ¼ to engender, bring forth. As combustion of the ‘inflammable air’ always produced water, it was characterized by the word ydvr (hydro) ¼ water, hydroge`ne (H) in French and hydrogen in English. The German name Wasserstoff means the identical (Wasser ¼ water; Stoff ¼ material). The major property of the gas causing the ‘remarkable flame’ was thought to be the formation of acids. Therefore, the word ojys (oxys) ¼ acid became characteristic for oxyge`ne (O) in French, oxygen in English and Sauerstoff in German (sauer ¼ acid, sour). Referring to the gas discovered by Daniel Rutherford, Lavoisier pointed out: nous l’avons donc nomme´ azote, de l’a privatif des Grecs, et de zvh, vie, ainsi la partie non respirable de l’air sera le gaz azotique (we, therefore, named it azote, from the Greek alpha privativum and from zvh, life, thus the not respirable part of the air will be the azotique gas).

Following the same thought, the gas was named Stickstoff in German, derived from the verb ersticken ¼ to suffocate. In 1790, Jean Antoine Chaptal proposed the name nitroge`ne. The Greek word nitron [nitron] was used for saltpetre (potassium nitrate), thus the name nitroge`ne means ‘making soda/saltpetre’ (Van der Krogt, 2003b). The latter name was adopted in English as nitrogen. With carbon and sulphur known for a long time and the three elements nitrogen, oxygen and hydrogen discovered before the end of the 18th century, interest increased in the quantitative analyses of elements in various organic materials at the beginning of the 19th century. Mulder (1838) carried out a large series of analyses in what he called

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the ‘most important substances in the animal kingdom’ – fibrin, albumin and gelatine. Regularly, he found that these substances contained more than 50% carbon, about 22% oxygen, between 15.5% and 16% nitrogen, about 7% hydrogen, and less than 1% phosphorus and sulphur. He stated: La matie`re organique, e´tant un principe ge´ne´ral de toutes les parties constituantes du corps animal, et se trouvant, comme nous verrons tantot, dans le re`gne ve´ge´tal, pourrait se nommer Prote´ine de prvteios primarius (the organic matter, being a general principle of all parts forming the animal body and to be found, as we shall soon see, in the plant kingdom as well, may be named Protein from proteios [Greek] ¼ primarius [Latin]).

Thus, the name protein was meant to indicate that organic compounds containing nitrogen are by no means adverse to life (azotique) but, on the contrary, are of primary importance and play a predominant role in biological processes. This thought was immediately taken up by Justus von Liebig who is often referred to as ‘father of agricultural chemistry’. Liebig (1840, p. 64) wrote: In dem humusreichsten Boden kann die Entwicklung der Vegetabilien nicht gedacht werden ohne das Hinzutreten von Stickstoff, oder einer stickstoffhaltigen Materie (In soil, even richest in humus, it is impossible to imagine development of plants without the presence of nitrogen or nitrogen containing material).

He then continues to explain that there is no reason for believing that N from the air can participate in processes of animals or plants and that, on the other hand, he had found strong correlations between the amount of ammonia taken up through the roots and the amount of gluten formed in grains. Further, he observed that the presence of P was essential for the transformation of N from ammonia into protein formed by plants. Liebig’s conviction that there were only three proteins and that these were transferred without any change from plants as food into animal tissues (Liebig, 1843) was challenged by the work of Voit (1872) who found considerable differences in N balances of dogs fed varying proportions of meat and gelatine. Thomas (1909) balanced N in his own body over periods in which he ingested a constant N-free basal diet of starch and sugar either alone or supplemented by different vegetable or animal products as sole sources of

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protein. From the results, he concluded that clear differences exist in the ‘biological value’ of the protein in different foods. Mitchell (1924), taking up the basic idea of Thomas (1909), defined the ‘biological value’ of a diet component fed to rats as the percentage of absorbed N equivalent to the sum of metabolic faecal N, endogenous urinary N and retained N. A more complete review of the history of research and understanding of protein metabolism is given by Munro (1964). Amino acids were identified in the period between 1806 and 1935 (Meister, 1965). Once the biological function of these components of all natural proteins had been discovered, analyses of indispensable amino acids became more meaningful than the biological value of complete proteins. In non-ruminant nutrition nowadays, free amino acids are frequently used for upgrading natural proteins and requirements, as well as recommendations for supply, and are increasingly based on amino acids absorbed prior to the caecum, i.e. from the small intestine. Towards the end of the 19th century, fundamental differences between non-ruminants and ruminants with regard to utilization of N became obvious. Zuntz (1891), at the end of a review dealing with digestion of cellulose, addressed the finding that asparagine as the sole source of dietary nitrogen is worthless in dogs but has positive effects in ruminants. He proposed the hypothesis that nitrogen of asparagine and comparable amides might be incorporated into microbial protein, which then could be digested by ruminants. This is seen as the starting point of research into non-protein nitrogen (NPN) use in ruminants (Bergner, 1986). More than 50 years after Zuntz’s hypothesis, Loosli et al. (1949) presented concentrations of the ten essential amino acids in rumen material, faeces and urine of three sheep and two goats fed diets containing urea as the sole source of dietary N; the results were clear evidence of massive amino acid synthesis in the rumen. Lambs fed this diet gained about 100 g daily. Microbial synthesis of all amino acids was fully confirmed in rumen-fistulated calves by Duncan et al. (1953). Long-term feeding experiments in Finland finally proved that cows fed purified rations with urea and ammonium salts as the sole sources of N could not only survive but reproduce and produce moderate milk yields with normal composition over repeated lactations (Virtanen, 1966).

The potential of microorganisms to utilize NPN is not restricted to urea as a feed additive – it is also relevant for urea synthesized in the liver of their host animal. Simonnet et al. (1957) found in anaesthetized sheep that urea accumulated in the isolated forestomach filled with saline and concluded the existence of a cycle by which urea present in the blood was returned into the digestive tract. Schmidt-Nielsen et al. (1957) showed in a camel on very low N intake that not only quantities of urea in the urine were minimized but also that intravenously infused urea was retained in the body. From measuring urea clearance rates and glomerular filtration rates, these authors concluded that fractions of the filtered urea excreted were about 40% during normal N intake but only 1–2% during extremely low N intake. One way for blood urea to enter the rumen is via saliva, but there is also a direct transfer through the mucosa of the rumen wall, which has been reviewed by Houpt (1970). The role played by bacteria adhering to the rumen wall in the transfer of urea N from the blood into the rumen was reviewed by Cheng and Costerton (1980). Rapidly growing knowledge about factors influencing the quantity of amino acids flowing to the duodenum of cattle led to the consequence that digestible crude protein could no longer be regarded as an adequate basis for describing requirements and supply of N in ruminants, and alternative systems were proposed (Roy et al., 1977; Satter and Roffler, 1977; Ve´rite´ et al., 1979; Madsen and Hvelplund, 1984; Rohr et al., 1986). The present state of the art with respect to N requirement and systems of feed evaluation is reviewed in Chapter 2 of this book. Chapters 3 and 4 summarize the present knowledge about N metabolism in ruminal microorganisms and discuss potential strategies for improving the efficiency of N utilization by manipulation of microbial metabolism.

1.3

Resources of N and Phosphate as Plant Nutrients

Only very low concentrations of N are found in rocks from which soil originates. Fixation of N2 from the air can be achieved by some microorganisms, free-living or in symbiosis with higher plants. Among the latter, legumes are of particular

Interactions between Cattle and the Environment

importance in agriculture. When a certain concentration of organic matter has accumulated in the soil, primarily through microbial fixation of N2 , organically bound N can be mobilized again into low-molecular-weight compounds like amino acids, ammonia and nitrate, which are taken up by plant roots. Nitrogen may be lost from soil by diffusion of nitrate into groundwater or by volatilization of ammonia. Rocks are the major reservoir of phosphates. When soil is formed from rocks, orthophosphate is formed from apatites. Phosphorus in the soil is present on the surface of various adsorbents as precipitates with several inorganic cations or as organically bound phosphate. The central pool through which these separate pools communicate is the small amount of ionized orthophosphate in the soil solution. Plants and soil organisms take up ionized phosphate. Phosphorus may be lost by diffusion of phosphate into the groundwater or by erosion of adsorbing particles into surface water. Insufficient replacement of nutrients extracted by plants from the soil of fields was a major reason for low crop yields with the consequence of increasing poverty and famines at regular intervals in Europe over long periods. In the 19th century, acidulating bones with the aim of increasing the solubility of phosphate was attempted

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empirically in several places and finally the industrial production of superphosphate, predominantly from bones, was developed. Considerable quantities of plant nutrients were transported from South America to Europe in the form of Chile nitre (mainly sodium nitrate) mined in the Atacama desert and of guano, excreta of birds on the Peruvian islands, rich in salts of nitric acid and phosphoric acid. Phosphate ores were first mined in relatively small amounts in the 1840s in England, France and Spain and later in other countries; today most of the phosphate fertilizer and phosphate chemicals are produced from phosphate rock (Beaton, 2003). Table 1.1 shows today’s important areas of phosphate mining. Phosphate-containing ore bodies are finite, non-renewable resources. Reserves are defined as deposits that may potentially be feasible at some time in the future. Reserve base is that part of an identified resource that meets specified minimum production practices. Reserve and reserve base at present cost less than $36/t and $90/t, respectively. At current production levels, the world’s reserve and reserve base are estimated to last for less than 100 years and about 340 years, respectively (Roberts and Stewart, 2002). The most important step towards overcoming the shortage of plant nutrients was taken in 1909

Table 1.1. World phosphate rock production, reserves and reserve base. (From Roberts and Stewart, 2002.)

Country Morocco/Western Sahara Tunisia Senegal Togo South Africa USA Brazil Jordan Israel Syria China Russia Other countries Total (rounded)

Production 1997–2001 (thousand t/year)

Reserves (million t)

Reserve life (years)

Reserve base (million t)

Reserve base life (years)

25,346 8,697 1,860 1,917 3,152 44,851 4,875 6,350 4,487 1,955 24,134 11,020 12,364

6,281 110 55 33 1,653 1,102 364 992 198 110 1,102 220 1,322

248 13 30 17 524 25 75 156 44 56 46 20 110

23,142 661 176 66 2,755 4,408 408 1,873 882 882 11,020 1,102 4,408

913 76 95 34 874 98 84 295 196 451 457 100 357

151,000

13,224

88

51,794

343

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E. Pfeffer and A.N. Hristov

when Fritz Haber informed the directors of Badische Anilin und Soda Fabrik (BASF) that his search for combining nitrogen and hydrogen to ammonia had functioned successfully in the laboratory. Carl Bosch then found ways of making the principle work under industrial conditions. By application of the Haber–Bosch process, about 4000 t of ammonia were produced in 1913, and today the global output of ammonia is estimated at about 130 million t/year (Smil, 1999). Due to this invention, the ‘not respirable air’ discovered by Daniel Rutherford became the infinite raw material for production of nitrogen fertilizer.

1.4

Elementary Balances in Animal Production

Chemical elements can be neither produced nor destroyed in the animal’s metabolism. They can only be transferred from one form into another and a very great part of research in animal nutrition is simply based on balancing elements. This is demonstrated in Table 1.2 for five elements in a dairy cow weighing 650 kg, assumed to produce 30 kg of milk daily. Further it is assumed that body mass and composition are constant. In order to cover the requirements of energy and all nutrients for maintenance and production, this cow is assumed to consume 50 kg of a total mixed ration (TMR) containing 40% dry matter (DM) plus 80 l of water per day. A more detailed investigation may disclose that this cow daily excretes 40 kg of faeces containing

15% DM and 30 l of urine and that microbial fermentation in her digestive tract causes a daily emission of 500 l methane (CH4 ). Finally, her daily consumption of oxygen from inspired air may amount to 6000 l and a corresponding volume of carbon dioxide (CO2 ) may be expired daily. When elements are analysed in dietary DM, drinking water, milk and all excreta, then daily movements of the analysed elements into and out of the animal’s body can be calculated, as shown in Table 1.2 for carbon, hydrogen, oxygen, N and P. The efficiency by which the consumed elements are turned into compounds of milk in this example is 7% for oxygen, 23% and 25% for carbon and hydrogen and about 30% for N and P, respectively. Only in recent years, potential impacts on the environment of that unutilized part of the ingested elements has found scientific interest. Expiration of CO2 is not a net contribution to the greenhouse effect (global warming) because carbon contained in the feed must have been captured from CO2 in the atmosphere in the preceding period of vegetation. Expired CO2 is thus recycled into the atmospheric pool and is ready for again getting captured for photosynthesis according to the equation: 6CO2 þ 6H2 O ! C6 H12 O6 þ 6O2

(1)

Carbon contained in faeces and urine will finally be oxidized to CO2 when exposed to aerobic conditions and the same should happen to methane, and thus the cycle of carbon between

Table 1.2. Approximate balance of five elements in dairy cows producing 30 kg of milk daily and fed according to common recommendations (g/day)a. Element Input: Dietary dry matter Respiration (O2) Output: Milk Methane Faeces Urine Respiration (CO2) Metabolic water a

Carbon

Hydrogen

Oxygen

Nitrogen

Phosphorus

9000

1200

8500 8500

550

90

2100 300 2600 400 3600

300 100 300 100

1200

170

27

2600 400 9600 3200

170 210

62 1

400

Constant body mass and composition assumed; for further assumptions see text.

Interactions between Cattle and the Environment

atmospheric carbon dioxide and organic matter is completed. Methane and its oxidation products, especially carbon monoxide, have great importance for the chemistry of the atmosphere (Crutzen, 1995), but this point will not be followed in this book. Oxidation of hydrogen to water in the metabolic chain of reactions is the principle for providing the organism with metabolizable energy. Water formed in this way does not have any impact on the environment. Nitrogen is excreted in the urine mostly as urea. When contaminated with faeces, this urea may readily be hydrolysed by microbial urease according to the equation: OC(NH2 )2 þ H2 O ! CO2 þ 2NH3

(2)

When excreta are applied to the soil, ammonia is formed and may be taken up by plants through their roots, either directly or after conversion to nitrate. If excreted N accumulates in concentrations exceeding the capacity of plants, considerable emissions of ammonia into the air and nitrate into groundwater may occur. Both phenomena are regarded as having impact on the environment. When cattle are grazing on pasture, enrichment of N will result in those spots where the animals urinate and enrichment of P will be found where they defecate. Thus, a certain degree of horizontal movement of nutrients will be found within the grazed paddocks. Principally, the same phenomenon has to be registered on a much larger scale as a consequence of transporting great quantities of concentrate feeds, regardless of whether grains or by-products of the food industry, from the site of their production into areas of high animal density.

1.5

Environmental Regulations in the USA and the European Union

Although progress has been made (Børsting et al., 2003), N and P are routinely overfed to ruminants, which, in combination with the continuous trend to concentrate animal units in intensive animal systems, leads to nutrient surpluses at farm and system levels ( Jonker et al., 2002; Ondersteijn et al., 2002; Dou et al., 2003). Compared to crops,

7

production of nutrients from farm animals, particularly ruminants, is an inherently inefficient process (Domburg et al., 2000; Ondersteijn et al., 2002). The efficiency of utilization of dietary nutrients for milk or meat production is a simple formula: Efficiency ¼

Nutrient in usable products Nutrient intake

(3)

A reduction of the denominator or an increase of the numerator will enhance efficiency, i.e. less N input and/or greater milk N output will result in an increased efficiency of conversion of dietary N into milk N, for example. Crude protein content and composition of the diet can have a profound effect on N losses and ammonia release from manure (Swensson, 2003) and must be publicized by nutrition consultants and extension professionals as an immediately available tool for reduction of N losses from cattle operations. Alternatively, N (and P) from animal waste may be converted into valueadded products, thus reducing nutrient loads to soil and atmosphere (Cowling and Galloway, 2001). Management practices, however, often have minimal impact on milk N efficiency ( Jonker et al., 2002), although when backed by legislative actions, farm management is critical in controlling nutrient pollution from dairy operations (Ondersteijn et al., 2003). Similar conclusions can be drawn at whole-farm and agricultural system levels (De Vries et al., 2001). Concentration of livestock in large feeding operations has been associated with concerns regarding water and air quality and nuisance issues such as odour. In the USA, the Environmental Protection Agency (EPA) is the government body responsible for implementing environmental regulations, including regulations applicable to animal feeding operations (for details, see Meyer and Mullinax, 1999; Meyer, 2000; and Powers, 2003; most recent revisions can be found at the EPA web site, http:// www.epa.gov/npdes/caforule; Federal Register, Vol. 68, No. 29, 12 February 2003). In retrospect, the EPA rules regulating animal feeding operations (AFO) stemmed from the 1972 Federal Clean Water Act (CWA, Section 502) classifying beef feedlots as point sources of pollution. In 1974 effluent guidelines for feedlots were established and in 1976 regulations were issued defining Concentrated Animal Feeding Operations (CAFO) requiring National Pollutant Discharge Elimination System (NPDES) (Sweeten

8

E. Pfeffer and A.N. Hristov

and Miner, 2003). Under the current regulations, AFO are required to have an NPDES permit if the animals are fed or housed in a confined area for more than 45 days in any 12-month period and crops, vegetation, forage growth or postharvest residues are not sustained in the normal growing season over any portion of the lot or facility. Animal operations are grouped into large ($1000 beef cattle or dairy heifers, or $700 mature dairy cattle), medium (300 to 999 beef cattle or dairy heifers, or 200 to 699 mature dairy cattle) and small ( MP milk, and actual milk between −6 kg and +6 kg of MP-allowable milk (n = 149)

NE milk > MP milk, and actual milk between −6 kg and +6 kg of MP-allowable milk (n = 149)

50

1600

y = −3E − 06x2 + 0.0278x − 14.473 R 2 = 0.67

y = 0.4534x − 64.352 R 2 = 0.76

1400

40

1200 1000

30 800 600

20

400 10 1000

1500

2000

2500

3000

200 1000

1500

2000

2500

3000

MP (g/day)

MP (g/day)

Lys