Equine nutrition is the feeding of horses, ponies, mules, donkeys, and other equines. Correct and balanced nutrition is a critical component of proper horse care.Horses are non-ruminant herbivores of a type known as a "hind-gut fermentor." This means that horses have only one stomach, as do humans. However, unlike humans, they also have to digest plant fiber (largely cellulose) that comes from grass and hay. Therefore, unlike ruminants, which digest fiber in plant matter by use of a multichambered stomach, horses use microbial fermentation in a part of the digestive system known as the cecum to break down the cellulose.In practical terms, horses prefer to eat small amounts of food steadily throughout the day, as they do in nature when grazing on pasture. Although this is not always possible with modern stabling practices and human schedules that favor feeding horses twice a day, it is important to remember the underlying biology of the animal when determining what to feed, how often, and in what quantities.

The digestive system of the horse is somewhat delicate. Horses are unable to regurgitate food, except from the esophagus. Thus, if they overeat or eat something poisonous, vomiting is not an option. They also have a long, complex large intestine and a balance of beneficial microbes in their cecum that can be upset by rapid changes in feed. Because of these factors, they are very susceptible to colic, which is a leading cause of death in horses. Therefore, horses require clean, high-quality feed, provided at regular intervals, and may become ill if subjected to abrupt changes in their diets.Horses are also sensitive to molds and toxins. For this reason, they must never be fed contaminated fermentable materials such as lawn clippings.Fermented silage or "haylage" is fed to horses in some places; however, contamination or failure of the fermentation process that allows any mold or spoilage may be toxic.

Vitamins and minerals

Many commercially prepared vitamin and mineral supplements are available for horsesHorses that are not subjected to hard work or extreme conditions usually have more than adequate amounts of vitamins in their diet if they are receiving fresh, green, leafy forages. Sometimes a vitamin supplement is needed when feeding low-quality hay, if a horse is under stress (illness, traveling, showing, racing, and so on), or not eating well. Grain has a different balance of nutrients than forage, and so requires specialized supplementation to prevent an imbalance of vitamins and minerals.Minerals are required for maintenance and function of the skeleton, nerves, and muscles. These include calcium, phosphorus, sodium, potassium, and chloride, and are commonly found in most good-quality feeds. Horses also need trace minerals such as magnesium, selenium, copper, zinc, and iodine. Normally, if adult animals at maintenance levels are consuming fresh hay or are on pasture, they will receive adequate amounts of minerals in their diet, with the exception of sodium chloride (salt), which needs to be provided, preferably free choice. Some pastures are deficient in certain trace minerals, including selenium, zinc, and copper, and in such situations, health problems, including deficiency diseases, may occur if horses' trace mineral intake is not properly supplemented.