The horse is a hindgut-fermenting herbivore. That means most of the digestion of fibre takes place only in the caecum and the colon, after the feed has passed through the stomach and the small intestine. Feeding a horse should therefore imitate the natural way of taking in food: often, in small portions, and mainly as fibrous material (hay, grass). In nature, horses graze for up to 16 hours a day! Their digestive system is adapted to a slow, constant flow of fibre, not to infrequent, large meals rich in cereals.
The horse’s stomach is relatively small (about 8-15 litres) and works almost without a break. It does not stretch as it does in other animals, so portions that are too large can lead to overload and colic. In addition, the horse cannot vomit, which makes it particularly susceptible to indigestion. The small intestine is mainly responsible for digesting proteins and fats and for absorbing nutrients. Unfortunately, this process works effectively only with a limited amount of starch. Any excess passes on, into the large intestine. The caecum and colon are the centre of fermentation, where microorganisms break down plant fibre. As a result, the horse draws its energy mainly from volatile fatty acids, not, as a person does, from sugar or starch.
Disturbing this delicate balance can have very serious consequences. A horse’s diet should be based mainly on fibre, that is hay, grass and chaff with no added molasses. Fibre not only supplies energy; it also regulates the work of the gut, improves motility and has a beneficial effect on the bacterial flora. Cereals such as oats, barley and maize contain a lot of starch, which in excess can lower the pH in the large intestine and lead to serious disease, such as laminitis or fermentative colic. Feeding a large amount of concentrate is a common mistake. For most of the day the horse should have access to forage, which supports the natural rhythm of digestion and reduces the risk of ulcers. It also needs constant access to fresh, clean water. Dehydration can slow gut motility and lead to impactions.
And what about supplementation and extras? When the foundations of the diet, that is hay and grass, are of suitable quality, often not much more is needed. In sport horses, horses recovering from illness, older horses or those with metabolic problems, however, it is worth discussing the feeding with a nutritionist. Supplements such as electrolytes, feed yeast or probiotics can support digestion, but they will never replace a well-balanced foundation.
To sum up… The horse’s digestive system is a precise but delicate system that needs the right approach to feeding. The key is a natural diet, based mainly on fibre and regular access to forage. Avoiding excess starch, hay of suitable quality and care over hydration are simple rules that keep a horse healthy for many years.