Proper formulation of diets for horses depends on adequate knowledge of their nutrient requirements. These requirements depend on the breed and age of the horse and whether he or she is exercising, pregnant, or lactating. A great deal of new information has been accumulated since the publication 17 years ago of the last edition of Nutrient Requirements of Horses. This new edition features a detailed review of scientific literature, summarizing all the latest information, and provides a new set of requirements based on revised data. Nutrient requirements for all classes of horses and ponies during various physiological life phases are established. Readers will appreciate a web-based computer program (which will be made available on the National Academies website) for determining nutrient requirements based on the documentation and equations contained in the book. Also included is updated information on the composition of feeds, feed additives, and other compounds routinely fed to horses. The effects of physiological factors, such as exercise, and environmental factors, such as temperature and humidity, are covered, as well. Nutrient Requirements of Horses also contains information on several nutritional and metabolic diseases that horses often have. Designed primarily as a reference, both practical and technical, Nutrient Requirements of Horses is intended to ensure that the diets of horses and other equids contain adequate amounts of nutrients and that the intakes of certain nutrients are not so excessive that they inhibit performance or impair health. Nutrient Requirements of Horses is primarily intended for animal nutritionists, veterinarians, and other scientists; however, individual horse owners and managers will also find some of this material useful. Professors who teach graduate courses in animal nutrition will find Nutrient Requirements of Horses beneficial as a textbook.