Horses will generally not fast (go without feed) for longer than 3 to 4 hours at a time. They have evolved to eat forages in small amounts frequently. Eating grain is not actually natural for a horse in the wild, and some horses are adversely affected by the over-feeding of grain. Excess carbohydrates can change the intestinal microflora of a horse. Although working horses may require the extra calories obtained from grain, high quality hay will often suffice for maintenance of companion or lightly worked horses. Access to free choice salt and water is also recommended. While some individuals prefer to use mineralized salt blocks, some research shows they can cause colic.

Colic is the term for discomfort in the gut due to the intestinal wall being stretched by gas or fluid. The most common sign of colic is a horse’s refusal to eat. Since horses do not generally fast for more than a few hours, this is often the earliest recognized sign. Horses may also show signs of pain, including kicking or biting at their bellies, sweating, refusal to drink, and rolling.

Horses are also generally gluttonous and will over-eat if given the opportunity, which is why small, frequent meals are best. Horses cannot vomit. If a horse shows signs of passive regurgitation, the stomach is overfull. This is a very bad situation, and requires veterinary intervention in many cases.

Choke is obstruction of the esophagus, usually caused by a horse eating too quickly or by the horse trying to swallow large masses of food (poor teeth - improperly chewed forage). The situation is not immediately life threatening and often resolves on its own. A horse that bolts its food can sometimes be slowed by placing large rocks in its grain feeder or feeding hay first, although neither may work.

Coprophagia is the act of eating feces. There are many reasons that may be behind this behavior. Foals commonly eat their dam’s feces. It is thought that this behavior acts to establish gut microflora, to obtain nourishment from partially digested foodstuffs, or due to a recognition effect. Feral horses may also eat feces when their food supplies are low.

Pica is the ingestion of foreign materials, such as sand, wood, bedding, or other substances in the animal’s environment. While the horse may be lacking crucial minerals (such as copper, zinc, or salt) or vitamins, it is believes that many horses exhibit this behavior due to boredom, as pica is seen in horses with balanced diets.