Control is via highly complex neurological and hormonal mechanisms involving signaling from nutrients such as glucose and volatile fatty acids, gut fill, the gut hormone Ghrelin which stimulates hunger, and the hormone Leptin from fat tissue which suppresses appetite. Poor appetite can be an issue for performance horses, especially racehorses. Gastric ulceration EGUS is the first cause to be eliminated as gut pain depresses appetite. The old favorite remedy was Vitamin B12 which is required to metabolize propionate which is increased by high starch diets but it’s use is questionable because it is very rapidly cleared from the body. Thiamin B1 requirements are also elevated by hard exercise so B Vitamin supplementation may have some value. It should also be remembered that horses which are dehydrated, or electrolyte depleted, will often refuse food until those imbalances are rectified.