Horses, as well as other animals, should be fed according to their nutritional needs. Horses’ nutritional requirements are based on stage of production and activity. The categories that determine nutrient requirements are maintenance, gestation, lactation, growth and work. The horse is then fed to meet those nutrient needs. Maintenance requirements are those requirements needed for a horse to simply maintain its present body status, neither gaining nor losing weight. Pregnant mares during late gestation require additional nutrients above maintenance to sustain body weight and provide for the growing fetus.
Nutritional requirements dramatically increase during lactation. This is the stage of production when a mare nurses a foal. Nutrients are needed to maximize milk production and insure adequate foal growth, as well as maintain adequate condition for the mare. Young horses will have specific nutritional requirements during the weaning, yearling, long yearling and 2-year-old growth phases. Nutrient needs will also change based on the length and difficulty of exercise or training programs. Work nutritional requirements are categorized as light (Western and English pleasure), moderate (ranch work, roping, jumping) and intense (polo, race training).
Many times a horse will have nutrient needs for more than one stage of production or activity. Therefore additional nutrients above maintenance, gestation or growth must be provided in the diet. For example, a 2-year-old horse on a moderate work program would have to meet maintenance, growth and work nutritional requirements. Also, a mare in late gestation that is still being used to work cattle would also have to meet nutritional requirements for maintenance, gestation and work. Nutrient requirements are based on the total of all functions performed.
"TNH0004-Nutritional Needs of Horses," The University of Tennessee Agricultural Extension Service, TNH-0004 3/03 E12-4415-00-020-03, http://trace.tennessee.edu/utk_agexani/17