Equine Digestive Tract Structure and Function
| Author: | Dr. Bob Wright, Veterinary Scientist, Equine and Alternative Livestock/OMAFRA |
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| Creation Date: | 01 September 1999 |
A horse has the same requirements for energy, protein, vitamins and minerals as other animals but differs in the type and function of its digestive system, falling between a ruminant and non ruminant.
Non ruminants (humans, pigs and dogs) digest carbohydrates, protein and fat by enzymatic action. Ruminants (cattle, sheep and deer) use bacteria in the fore stomachs to digest fiber by fermentation and use enzymatic digestion in the small intestines.
In the horse, all true digestion is by enzymatic digestion and takes place in the fore gut ahead of the cecum. This accounts for 52-58% of the crude protein digestion and virtually all soluble carbohydrate digestion (fiber excluded). (1) In addition, bacterial or microbial digestion of fibre occurs in the cecum and colon where large quantities of volatile fatty acids are produced through fermentation and are subsequently absorbed. This dual system allows the horse to digest simple carbohydrate sources such as starch from grain in the fore gut. Fibrous sources such as oat hulls, soy hulls, beet pulp, hay and pasture are digested in the hind gut.
For enzymatic and microbial action to digest feed efficiently, the horse needs healthy teeth to grind feed and allow enzymes and bacteria to attack the plant cell walls. Teeth should be examined during the annual health check to ensure that they are wearing normally and are effectively grinding the feed.
The capacity of the stomach of the horse is only about 8-15 litres (eight quarts or two gallons), which makes it difficult to understand how a horse can consume large amounts of food or water. The emptying time of the stomach after filling can be about 12 minutes, and the rate of passage down the small intestine is about 1 ft/min. The net result is that food can go from the mouth to the cecum in about 1½ hours. The small volume of the stomach and rapid passage of food from the stomach is the reason horses eat almost continuously, thus the name "hay burners."
