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Summary The National Research Council has published five previ- quirements have been related to body weight, and guidelines ous editions of Nutrient Requirements of Horses. A great for adjusting the energy intake to meet the needs of adult deal of research on the nutrition and feeding of horses has horses with various levels of voluntary activity are given. A been conducted since the fifth edition was published in method that enables users to estimate expected body weight 1989. The Sixth Revised Edition contains updated informa- of growing horses at any age from expected mature body tion on the nutrient requirements of domestic horses and weight has been proposed. The effect of exercise on energy ponies, as well as expanded information on general consid- requirements is discussed in this chapter, as are the effects erations for equine feeding management. This report in- of excessive and deficient energy intakes on horses. cludes a discussion of feeding management of other equids, Chapters 2 (Carbohydrates) and 3 (Fats and Fatty Acids) such as donkeys and wild equids kept in captivity. One chap- address the main energy-containing compounds used by ter provides information on the feeding management of horses. These chapters include information on the metabo- horses with nutritionally related disorders. A new web-based lism of carbohydrates and fats during exercise. Chapter 2 computer program has been developed that will assist users discusses the classification of carbohydrates in horse feeds, in determining the nutrient requirements of domestic horses and Chapter 3 provides extensive review of the effects of and ponies of specific physiological classes. feeding fat-supplemented diets to horses. In 2005, the American Horse Council estimated that the A comprehensive review of protein and amino acid nutri- number of horses in the United States exceeded 9 million and tion of horses is presented in Chapter 4. Protein require- that more than 2 million people were involved in horse own- ments are expressed in grams of crude protein, and lysine re- ership. The economic impact of the U.S. horse industry was quirements are estimated. This chapter includes a discussion estimated to be more than $100 billion. Horses are used for of protein digestibility and protein quality. recreational purposes, sport (e.g., racing, polo, and Olympic The requirements of horses for macrominerals and mi- events), exhibition, breeding, ranch and farm work, and even crominerals are found in Chapter 5. There has been a sub- therapy. Type of use, age, and physiological state affect the stantial amount of research on the mineral nutrition of nutrient requirements of horses. Horses are distributed horses since the previous edition of this document was pub- broadly across the United States and the world, where they lished in 1989. This chapter includes an expanded discus- are subjected to a variety of climates and housing conditions. sion on several topics in mineral nutrition, including the ef- Effective feeding management practices must consider many fect of exercise on mineral requirements, and the addition of factors, including nutrient requirements, environmental con- chromium and silicon to equine diets. ditions, and available feeds. This report addresses not only Chapter 6 addresses the vitamin requirements of horses. the nutrient requirements of horses, but also provides infor- A review of the literature revealed that previous recommen- mation on feeds, feed processing, and feeding behavior of dations for several vitamins were based on extremely lim- horses. It is expected that professional nutritionists, veteri- ited data. There have been a few new studies on vitamin nu- narians, feed manufacturers, researchers, teachers, students, trition in horses since 1989, and these studies were used to and horse owners will use the information. evaluate previous vitamin requirements. However, the com- Energy systems and energy requirements of horses are mittee relied on previous recommendations as a basis for the discussed in Chapter 1. The energy needs of horses for current estimates of requirements for several vitamins. maintenance, reproduction, lactation, growth, and exercise The section of the publication dealing with water re- are expressed in units of digestible energy. Maintenance re- quirements of horses has been significantly expanded. 1

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2 NUTRIENT REQUIREMENTS OF HORSES Chapter 7 discusses water requirements, factors affecting untary feed intake. This chapter also addresses the relation- water requirements, and water quality. ship between dietary management of horses and the excretion Feeds and feed processing are covered in Chapter 8. This of nutrients into the environment. Chapter 12 covers several chapter includes an extensive discussion of forages and unique aspects of equine nutrition, such as feeding the orphan the factors affecting forage composition. Grains, byproduct foal and feeding horses in very hot or very cold weather. feeds, protein supplements, vitamin supplements, and min- Chapter 12 also addresses the interactions between feeding eral supplements are also discussed. The effect of feed pro- management and several disorders such as colic, laminitis, re- cessing on nutrient digestibility and site of nutrient absorp- current airway obstruction, polysaccharide storage myopathy, tion is also reviewed. Chapter 9 describes feed additives that and gastric ulcer syndrome. The interaction between nutrition affect feed characteristics (such as colors, antioxidants, fla- and developmental orthopedic disease is also discussed. A vors, and pellet-binders), as well as additives that are in- new addition to this publication is Chapter 13, which summa- tended to affect animal health. rizes the existing information related to the feeding manage- The implementation of a successful feeding program de- ment of wild equids in captivity as well as donkeys. pends on an accurate assessment of the nutritional value of The sixth revised edition of Nutrient Requirements of the feed, as well as an understanding of the nutrient require- Horses concludes with Chapters 14 and 15, which cover ra- ments of an animal. Therefore, Chapter 10 addresses feed tion formulation and the equations used to develop the com- analysis. This chapter reviews many of the analytical proce- puter program that accompanies this document. In addition, dures currently available for feed analysis, with particular the document contains sample tables that list the nutrient re- emphasis on carbohydrates and proteins. Chapter 10 in- quirements of selected types of horses, feed composition ta- cludes a schematic that compares several systems used to bles, and a table summarizing the composition of mare’s classify carbohydrates in animal nutrition. milk. Users should recognize that many recommendations Chapter 11 reviews the existing literature pertaining to for ponies and draft horses have been extrapolated from data feeding behavior in horses and also provides guidelines for obtained using light horses. Therefore, it is suggested that general considerations relating to feeding management. In- the recommendations for ponies and draft horses be applied cluded in this chapter is a discussion of factors affecting vol- with discretion.