Horses have relatively small stomachs whose capacity constitutes only about 7 to 8% of that of their gastrointestinal tract, as compared to 60 to 70% for cattle.
This limits the amount that can be eaten in a single meal. A small stomach is an advantage for enhancing wild horses’ ability to flee from danger, and has no disadvantage for them since they are on pasture and able to eat small amounts continually. Horses on pasture spend 50 to 70% of their time, 24 hrs/day, grazing, during which small amounts of grass are ingested continually during the grazing periods. Regardless of the type of feed (hay, grain, or a complete pelleted feed), if it is available, most horses will eat hourly during the day and every 2 to 3 hours during the night. However, even when the feed is always available, the amount of time spent eating decreases from 50 to 70% when on pasture, to 30 to 70% when fed only hay, to 35 to 40% when fed a complete pelleted feed, and to 13 to 19% when fed a grain mix only. The decreased amount of time spent eating means more feed is consumed at one time. The amount consumed at one time is even greater when feed is not always available, as is the case and necessity for most horses not on pasture.
The greater the amount consumed at one time, the greater the stomachs distention, increase in gastrointestinal motility, and alteration it causes in the horse. However, horses can safely be fed even a high-grain diet as infrequently as twice daily when the total amount of feed is no more than the amount needed for maintenance, which would be up to 0.8 to 0.9 lb of grain/100 lbs body weight (0.8 to 0.9 kg/100 Kg) daily. However, for safety a maximum of one-half this amount of grain at a single feeding is recommended. To prevent digestive dysfunctions (excessive gas production, colic, laminitis, and impaired fiber fermentation) grain intake in the horse fed 2 to 3 meals daily should be limited to about 0.5 lb of grain/100 lbs body weight (0.5 kg/100 kg) per feeding. When grain ingestion exceeds these amounts, there is a dramatic increase in the amount of starch that escapes digestion and absorption from the small intestine, which greatly increases the risk of these problems.
Infrequent meal-induced changes in intestinal motility and blood flow increase the risk and occurrence of colic, a disease primarily of stabled or paddocked horses. This major disease of horses is uncommon in those on pasture. Since these changes, which increase the risk of colic, do not occur in response to small amounts consumed frequently, their occurrence and, therefore, the risk and occurrence of colic in horses not on pasture, can be decreased by: (1) having any forage, but preferably long-stem hay, available for the horse to eat to satiation and for as much of the time as possible; (2) feeding as frequently, at as regular, and at as even intervals as practical; and (3) feeding as little grain as necessary. Long-stem hay or pasture forage should be the basis for all feeding programs, and grain should be fed only if necessary and in as small amounts as possible. This doesn’t mean that grain shouldn’t be fed if desired or needed, but that forage should constitute the majority of the feed consumed. Two exceptions would be for the horse with poor teeth that may do better on a complete pelleted feed and/or more grain, and when good-quality forage is poorly available or considerably more expensive than grain.
In summary, it is recommended that all feeds be fed to all horses: (1) in equally divided amounts, (2) as near the same time each day and at as even intervals as practical, and (3) at least twice daily, but as many more times daily as practical. If the amount of grain fed is small (less than 0.25 lb/100 lbs bw daily) there may be little advantage in feeding it more than once daily. Feed working horses, lactating mares, and growing horses receiving large amounts of feed (an amount equal to more than 2.5% of their body weight daily) at least 3 times daily. It may be of benefit to feed grain to horses in intense training or use 4 to 5 hours prior to exercise, and not to feed them for at least one hour after strenuous exertion.
This article is from "Feeding and Care of the Horse", second edition, by Lon D. Lewis, Lippincott Williams & Wilkins, 1995. Reprinted with permission from the publisher.