The horse has a different digestive system than other farm animals. Although the horse has a single compartment stomach (like humans, pigs and dogs), the horse can utilize roughage like a cow or sheep which are ruminants (animals that use four stomachs to break down forages). This is possible because the horse has an unique type of large intestine.

The principle organs of digestion include salivary glands and teeth, stomach, small intestine, caecum, large colon, small colon and rectum. The liver and pancreas also contribute to the digestive system. The total length of the system is about 27 meters (90 feet) and the capacity is about 227.25 litres (50 gallons). The complete digestive process, from time of eating until the expulsion of the feces takes 3 to 4 days.

The Salivary Glands and Teeth
The digestive process begins in the mouth where the food is ground up and mixed with saliva by the molars. Saliva is discharged into the mouth from ducts located inside the cheeks, on the floor of the mouth and under the tongue. Saliva facilitates swallowing and helps convert the starches in the food into sugar. The rate of flow of the saliva is determined by the moisture content of the feed. Grinding is accomplished by the lateral (side-to-side) movement of the lower jaw against the upper jaw. If your horse has difficulty eating grain or is not doing well, check its teeth. Floating or rasping (usually a veterinary procedure) of the horse's molars and pre-molars as necessary will improve digestion.

After the food has been ground and throughly mixed with saliva, it is moved to the back of the mouth where the muscle of the pharynx force the food into the esophagus and into the stomach. Food moves down through the esophagus by successive waves of muscular constriction. These muscles only allow movement in one direction and prevent the animal from vomiting.

Stomach
In the stomach, glands located on approximately half of the stomach lining secrete gastric juices which are added to the saliva-soaked food. Gastric juices are slightly antiseptic and consist mainly of water, 0.3% hydrochloric acid and enzymes (pepsin). The action of the pepsin breaks down vegetable fats and changes proteins into a form that can be absorbed by the body. The food warms up to body temperature and, with the fluid conditions prevailing inside the stomach, the food begins to break down. The enzymes work best when the stomach is less then full.

Small Intestine
The small intestine is suspended from the underside of the backbone by a membrane called the mesentery. The intestine, like the stomach, secretes digestive juices through intestinal glands. Enzymes from the liver (bile) and pancreas are also secreted. The rate at which the food is broken down is sped up. The food breaks down into small molecules that are absorbed through hair-like villi that covers the walls of the intestine.

Caecum
The caecum is the first part of the large intestine. It is a unique structure that allows the horse to utilize roughage because of micro-organisms that help to break down woody material. It is also known as the water gut because it has a capacity of about 36 litres (8 gallons). In addition to digesting roughage and absorbing nutrients, it serves as a reservoir for storing water for the system.

Large Colon
In the large colon the bacterial action continues to break down the fibrous portion of the food, releasing carbohydrates. This action can take several days, which is the reason that the large colon is so large; three to four metres (10-12 feet) long, about 25 centimetres (10 inches) in diameter and can hold about 91 litres (20 gallons).

Small Colon
In the small colon, much of the fluid content is re-absorbed into the horses body.

Rectum
When the residue of the food moves into the rectum, it is pressed into the shape that characterizes horse droppings. The droppings of a healthy horse consist of 25% solid material and 75% water.

The feces from your horse can be an indication of their health. Check them routinely for undigested grain (it is normal for some whole oats to pass through) and any sudden change in consistency, color, odour or amount. Any of these conditions could be the first symptoms of a more serious problem.