The National Research Council has published five previous editions of Nutrient Requirements of Horses. A great deal of research on the nutrition and feeding of horses has been conducted since the fifth edition was published in 1989. The Sixth Revised Edition contains updated information on the nutrient requirements of domestic horses and ponies, as well as expanded information on general considerations for equine feeding management. This report includes a discussion of feeding management of other equids, such as donkeys and wild equids kept in captivity. One chapter provides information on the feeding management of horses with nutritionally related disorders. A new web-based computer program has been developed that will assist users in determining the nutrient requirements of domestic horses and ponies of specific physiological classes.
In 2005, the American Horse Council estimated that the number of horses in the United States exceeded 9 million and that more than 2 million people were involved in horse ownership. The economic impact of the U.S. horse industry was estimated to be more than $100 billion. Horses are used for recreational purposes, sport (e.g., racing, polo, and Olympic events), exhibition, breeding, ranch and farm work, and even therapy. Type of use, age, and physiological state affect the nutrient requirements of horses. Horses are distributed broadly across the United States and the world, where they are subjected to a variety of climates and housing conditions. Effective feeding management practices must consider many factors, including nutrient requirements, environmental conditions, and available feeds. This report addresses not only the nutrient requirements of horses, but also provides information on feeds, feed processing, and feeding behavior of horses. It is expected that professional nutritionists, veterinarians, feed manufacturers, researchers, teachers, students, and horse owners will use the information.
Energy systems and energy requirements of horses are discussed in Chapter 1. The energy needs of horses for maintenance, reproduction, lactation, growth, and exercise are expressed in units of digestible energy. Maintenance requirements have been related to body weight, and guidelines for adjusting the energy intake to meet the needs of adult horses with various levels of voluntary activity are given. A method that enables users to estimate expected body weight of growing horses at any age from expected mature body weight has been proposed. The effect of exercise on energy requirements is discussed in this chapter, as are the effects of excessive and deficient energy intakes on horses.
Chapters 2 (Carbohydrates) and 3 (Fats and Fatty Acids) address the main energy-containing compounds used by horses. These chapters include information on the metabolism of carbohydrates and fats during exercise. Chapter 2 discusses the classification of carbohydrates in horse feeds, and Chapter 3 provides extensive review of the effects of feeding fat-supplemented diets to horses.
A comprehensive review of protein and amino acid nutrition of horses is presented in Chapter 4. Protein requirements are expressed in grams of crude protein, and lysine requirements are estimated. This chapter includes a discussion of protein digestibility and protein quality.
The requirements of horses for macrominerals and microminerals are found in Chapter 5. There has been a substantial amount of research on the mineral nutrition of horses since the previous edition of this document was published in 1989. This chapter includes an expanded discussion on several topics in mineral nutrition, including the effect of exercise on mineral requirements, and the addition of chromium and silicon to equine diets.
Chapter 6 addresses the vitamin requirements of horses. A review of the literature revealed that previous recommendations for several vitamins were based on extremely limited data. There have been a few new studies on vitamin nutrition in horses since 1989, and these studies were used to evaluate previous vitamin requirements. However, the committee relied on previous recommendations as a basis for the current estimates of requirements for several vitamins.
The section of the publication dealing with water requirements of horses has been significantly expanded. Chapter 7 discusses water requirements, factors affecting water requirements, and water quality.
Feeds and feed processing are covered in Chapter 8. This chapter includes an extensive discussion of forages and the factors affecting forage composition. Grains, byproduct feeds, protein supplements, vitamin supplements, and mineral supplements are also discussed. The effect of feed processing on nutrient digestibility and site of nutrient absorption is also reviewed. Chapter 9 describes feed additives that affect feed characteristics (such as colors, antioxidants, flavors, and pellet-binders), as well as additives that are intended to affect animal health.
The implementation of a successful feeding program depends on an accurate assessment of the nutritional value of the feed, as well as an understanding of the nutrient requirements of an animal. Therefore, Chapter 10 addresses feed analysis. This chapter reviews many of the analytical procedures currently available for feed analysis, with particular emphasis on carbohydrates and proteins. Chapter 10 includes a schematic that compares several systems used to classify carbohydrates in animal nutrition.
Chapter 11 reviews the existing literature pertaining to feeding behavior in horses and also provides guidelines for general considerations relating to feeding management. Included in this chapter is a discussion of factors affecting voluntary feed intake. This chapter also addresses the relationship between dietary management of horses and the excretion of nutrients into the environment. Chapter 12 covers several unique aspects of equine nutrition, such as feeding the orphan foal and feeding horses in very hot or very cold weather. Chapter 12 also addresses the interactions between feeding management and several disorders such as colic, laminitis, recurrent airway obstruction, polysaccharide storage myopathy, and gastric ulcer syndrome. The interaction between nutrition and developmental orthopedic disease is also discussed. A new addition to this publication is Chapter 13, which summarizes the existing information related to the feeding management of wild equids in captivity as well as donkeys.
The sixth revised edition of Nutrient Requirements of Horses concludes with Chapters 14 and 15, which cover ration formulation and the equations used to develop the computer program that accompanies this document. In addition, the document contains sample tables that list the nutrient requirements of selected types of horses, feed composition tables, and a table summarizing the composition of mare's milk. Users should recognize that many recommendations for ponies and draft horses have been extrapolated from data obtained using light horses. Therefore, it is suggested that the recommendations for ponies and draft horses be applied with discretion.