Abstract
The National Research Council (NRC) published the Recommended Nutrient Allowances for Horses in 1949. The subsequent publication was renamed the Nutrient Requirements of Horses and the 6th revised edition was published in 2007. The document has increased in size and scope from the initial publication in 1949 that contained 29 pages to the most recent version with 341 pages. Several formats for expressing requirements (dietary concentrations or daily amounts) have been utilized. In addition, a variety of methods have been employed to determine the nutrient requirements of horses since 1949. Many of the requirement estimates are based on research studies with the target class of horse. However, some estimates have been derived from practical experience or extrapolated from other species and there is ample opportunity for future research related to many nutrients. Equine nutritionists may also explore additional methods to express the recommended daily nutrient intakes of horses.