Equine Digestive System

The horse is a continuous grazer and the digestive system is designed for the nibbling and eating of a variety of grasses while continuously walking, normally up to 17 hours a day. Confinement of horses and meal feeding high energy, high grain diets create a series of assaults with which the digestive system was not designed to cope. Developing an understanding of the digestive system, its process and limitations is essential for the successful feeding of the modern horse.

The Stomach

The equine stomach is unique in that it is relatively small in volume for the size of the horse, accounting for only 8% of the total gut capacity. Feed moves through the stomach in approx. 20 minutes.

Acid secretion in the stomach continuous. This acid is buffered by both the presence of food within the stomach and the production of saliva in response to chewing. The mucous content in the saliva also helps with swallowing. It is important that a horse has access to hay or pasture as they produce nearly twice as much saliva than if they are eating gran based feed. If a horse is fed short stem roughage such as chaff, grain and premixed feeds, will produce less saliva with the result of increased acidity in the stomach. This can impact directly in the incidence and occurrence of gastric ulcers.

Small Intestine

The small intestine is the principle site of digestion and absorption of protein, fats, starches and sugars. Horses lack a gall bladder and so bile is secreted continuously into the duodenum along with the pancreatic enzymes for digestion. If too much starch is fed and can not be digested in the small intestine then it will be fermented in the large intestine,, with the potential to cause serious digestive disturbances. It takes 2-8 hours for food to pass through the small intestine. The rate of passage is influenced by particle size, quantity and composition.

Hindgut

The hindgut is made up of the caecum and colon. They made up a large fermentation vat containing billions of bacteria and protozoa which ferment fibre and the remaining soluble carbohydrates into volatile fatty acids which are then absorbed into the bloodstream and utilised as a source of energy by the horse. Bacterial fermentation also produces certain B-group vitamins that are absorbed and utilised by the horse. It is also a major site of water absorption, as well as phosphorus and certain electrolytes. Bacterial fermentation releases a lot of heat and is important in thermoregulation of horses. This is why a horse can happily stand outside in low temperatures as long as they have plenty of forage.

In stabled horses on high grain, low fibre diets, chronic reduction in hindgut pH has been implicated in an increase in the incidence of stereotypic behaviours such as wind sucking and weaving, as well as an increase in the prevalence of 'hot headedness'.

The key to maintaining efficient digestive function in a horse is to mimic his natural diet as closely as possible:

base the diet on forage: ideally not less than 50% of total feed intake by weight.
keep a steady supply of forage available
balance diet around forage
make feed changes gradually, over 7-10 days
do not feed more than 2.5kg of grain or concentrate in any one meal.