Sheep Nutrition Ch 00 7/17/02 4:13 PM Page vii Contributors N.R. Adams, CSIRO Livestock Industries, Centre for Mediterranean Agricultural Research, Private Bag 5, Wembley, WA 6913, Australia E.F. Annison, Faculty of Veterinary Science, University of Sydney, Camden, NSW 2570, Australia A.J. Ball, Meat and Livestock Australia, c/o Animal Science, University of New England, Armidale, NSW 2351, Australia G. Caja, Departamento de Ciencia Animal y de los Alimentos, Facultad de Veterinaria, Universidad Autonoma de Barcelona, 08193 Bellaterra, Cerdanyola, Spain S.W. Coleman, USDA-ARS Subtropical Agricultural Research Station, 22271 Chinsegut Hill Road, Brooksville, FL 34601, USA R.L. Coop, Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian EH26 0PZ, UK J.L. Corbett, Animal Science, University of New England, Armidale, NSW 2351, Australia H. Dove, CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia J.M. Forbes, Centre for Animal Sciences, Leeds Institute of Biotechnology and Agriculture, University of Leeds, Leeds LS2 9JT, UK M. Freer, CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia D.A. Henry, CSIRO Livestock Industries, Centre for Mediterranean Agricultural Research, Private Bag 5, Wembley, WA 6913, Australia P.I. Hynd, Department of Animal Science, Adelaide University, Roseworthy Campus, Roseworthy, SA 5371, Australia G.J. Judson, South Australian Research and Development Institute, 33 Flemington Street, Glenside, SA 5065, Australia A.V. Klieve, Agency for Food and Fibre Sciences, Animal Research Institute, Locked Mail Bag No. 4, Moorooka, Qld 4105, Australia vii Sheep Nutrition Ch 00 7/17/02 4:13 PM Page viii viii Contributors S.O. Knowles, AgResearch Limited, Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand J. Lee, AgResearch Limited, Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand D.B. Lindsay, 66 Lantree Crescent, Trumpington, Cambridge CB2 2NJ, UK R.I. Mackie, Department of Animal Sciences, University of Illinois at Urbana- Champaign, 1207 W. Gregory Drive, Urbana, IL 61801, USA D.G. Masters, CSIRO Livestock Industries, Centre for Mediterranean Agricultural Research, Private Bag 5, Wembley, WA 6913, Australia R.W. Mayes, Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, UK N.P. McMeniman, School of Veterinary Science, University of Queensland, Brisbane, Qld 4072, Australia C.S. McSweeney, CSIRO Livestock Industries, Long Pocket Laboratory, Meiers Rd, Indooroopilly, Qld 4068, Australia T.G. McEvoy, Animal Biology Division, Scottish Agricultural College, Craibstone Estate, Bucksburn, Aberdeen AB21 9YA, UK J.V. Nolan, School of Rural Science and Agriculture, University of New England, Armidale, NSW 2351, Australia V.H. Oddy, Meat and Livestock Australia, Locked Bag 991, North Sydney, NSW 2059, Australia P.J. O’Reagain, Queensland Beef Industry Institute, Department of Primary Industries, PO Box 976, Charters Towers, Qld 4820, Australia J.J. Robinson, Animal Biology Division, Scottish Agricultural College, Craibstone Estate, Bucksburn, Aberdeen AB21 9YA, UK J.A. Rooke, Animal Biology Division, Scottish Agricultural College, Craibstone Estate, Bucksburn, Aberdeen AB21 9YA, UK R.D. Sainz, Department of Animal Science, University of California, Davis, CA 95616-8521, USA A.R. Sykes, Animal and Food Sciences Division, PO Box 84, Lincoln University, Canterbury 8150, New Zealand T.T. Treacher, 51 Western Road, Oxford OX1 4LF, UK G.C. Waghorn, AgResearch Limited, Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand R.H. Weston, 45 Park Street, Glenbrook, NSW 2773, Australia D.R. Woodfield, AgResearch Limited, Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand Sheep Nutrition Ch 00 7/17/02 4:13 PM Page ix Preface There are over 1 billion sheep in the world, with almost one-third of these located in China, Australia, New Zealand and the UK. The global production of wool (2.3 million t) and sheep meat (7.6 million t) tends to be concentrated in these countries. However, the developing countries of the world also have substantial populations of sheep and it is these which contribute the bulk of the world’s sheep milk production (8.2 million t). Regardless of country or production system, a feature common to most of the world’s sheep is that they rely very substantially, at times exclusively, on pasture, sown or natural, as their source of nutrients. Advances in nutrition science in the last half of the 20th century have helped us to define the processes of ruminant digestion and the nutrient requirements of the sheep. We know that short-chain (volatile) fatty acids, not glucose, are the product of ruminant carbohydrate digestion, and we can quantify the processes involved. With the current rapid advances in cellular genetics, we are increasingly able to define which rumen microorganisms are responsible for which processes. We have quantified much about the processes of protein breakdown in the rumen and the incorporation of the resultant ammonia into microbial protein. Together, these processes of fibre digestion and microbial protein production are the processes which allow ruminants to survive on low-quality roughages. Challenges remain in quantifying the importance of the synchrony of these processes under grazing conditions and in defining how we might breed pasture plants that achieve better synchrony. Perhaps an even greater challenge is that the reliance of the world’s sheep on pasture as their source of nutrients places a major constraint on our capacity to specify their daily intake of nutrients, especially in more extensive grazing systems. This, in turn, constrains our ability to predict absorption of nutrients, their interaction with body reserves of nutrients, ix Sheep Nutrition Ch 00 7/17/02 4:13 PM Page x x Preface and ultimately the way in which the grazing sheep partitions its nutrient supply between the processes of maintenance, production and reproduction. Reliance upon pasture also means that the grazing sheep is ‘at the mercy’ of any nutrient deficiency or toxicity present in the pasture and, as it consumes pasture, can also consume a raft of parasites that hinder health and production. These are not just academic issues, but issues of major economic importance. Sheep producers in developed countries increasingly face declining ‘terms of trade’, that is, reduced returns in the face of increasing costs. A worldwide reaction to this has been to seek to produce higher- value wool, meat and dairy products, while also reducing the cost and the environmental risks of sheep production systems. At the same time, increasing per capita incomes in both developed and especially developing nations are already increasing the demand for more and better meat and fibre products. In developing nations, this is manifest as increased demand for meat and for better-quality meat, while, in developed nations, there is increasing demand for meat products better attuned to consumer demands for a healthy diet. There is no doubt that issues such as these will be addressed by developing sheep genotypes better suited to new production systems, either by introducing new genotypes or by breeding within existing genotypes. Equally, there is no doubt that challenges remain for the science of nutrition. For example, in grazing systems, in which it is so difficult to define the nutrients actually consumed by sheep, how might we combine improved understanding of nutrient supply and of the mechanisms of growth at the cellular level to produce sheep meats with a nutrient composition, especially a lipid content and composition, more suited to human dietary goals? Similarly, how might we manipulate the diet of the grazing sheep to ensure the cheaper production of heavier fleeces with finer fibre diameters, to improve the incomes of wool producers? In assembling this book, our target reader has been the senior undergraduate or postgraduate student in animal science, the very population which, as animal nutrition professionals, will have to face and give advice to producers about the nutritional challenges facing sheep production systems in the future. As editors, we in turn challenged our chapter authors to produce 16 chapters that placed their respective facets of sheep nutrition in the context of the nutritional challenges faced by the grazing sheep. We thank all our contributors for so admirably achieving this, and hope that the resultant text will prove interesting and stimulating to students and practitioners of sheep nutrition science worldwide. M. Freer and H. Dove CSIRO Plant Industry Canberra Australia sheep nutrition Ch 01 7/17/02 3:56 PM Page 1 1 Nutritive Value of Herbage S.W. COLEMAN1 AND D.A. HENRY2 1USDA-ARS, Subtropical Agricultural Research Station, Brooksville, Florida, USA; 2CSIRO Livestock Industries, Wembley, Western Australia, Australia Introduction Herbage, the primary food for sheep, belongs to the group of feeds described as roughages. Roughages, in contrast to concentrates, are derived from the leaves and stems of pasture and crop plants and their dry matter (DM) contains a significant amount of cellulose (> 180 g kg−1). As herbage is grazed or cut from maturing and regrowing plants, the compo- sition of the feed and, with it, the ability of the feed to supply nutrients to the animal are in a continual state of change. For example, a young grow- ing pasture may support weight gains in excess of 300 g day−1 in young lambs, whereas a mature pasture may fail to maintain the weight of an adult sheep. This highlights the importance of establishing a robust system for defining the value of herbage for animal production, understanding how this value changes with the growth of the herbage and the needs of the animal and developing rapid methods for predicting changes that are occurring in the field. What is Nutritive Value? Nutritive value (NV) is a term used to quantify the presence and availabil- ity in a feed of nutrients that are required by the animal and to predict the productive output from the animal to which it is fed.