The equine gut, unlike that of the ruminant, has a relatively small stomach, approximately 9% of the total gut capacity. On the other hand it has a large hindgut, which consists of a colon and a caecum, representing 38% and 16% of total gut capacity, respectively. The equine rectum represents 7% of total gut capacity, and is extremely efficient at removing the water content of the droppings. The long small intestine represents 30% of total gut capacity, and it is rarely full; in fact, the total gut fill is usually less than one-third of total capacity.

All food has to be converted into a form that can be readily absorbed. First of all it has to be physically ground down by the teeth. Although each bolus of food will be chewed several times before swallowing, the equine’s food, unlike that of the ruminant, is allowed only one passage through the mouth. Forage needs to be chewed more than concentrated feeds. Not only is there more lateral excursion when long-fibred forage is chewed, but also the number of times it is chewed is greater. One kilogram of concentrated feed requires 1000 chews, while 1 kg of poor-quality roughage needs three times that number of chews. The condition of an equine’s teeth is extremely important, and therefore it is very important that they are checked regularly. However, an equine has only a finite amount of tooth to last its lifetime, unlike a rodent, and therefore only the sharp enamel overgrowths should be removed by regular rasping. The occlusal surface, unless there are other problems, should not be touched.

Fig. 8.1. Horses need to feed 18 out of every 24 hours.

After the physical maceration of the food, the animal has to break it down chemically, initially in the stomach and small intestine. This is the process of digestion, when the enzymes produced by the glands in the intestinal wall break down the food. Further along the gut there is a process of fermentation, where the animal is assisted by enzymes produced by bacteria, protozoa and fungi to break down the fibrous food into nutrients that can be absorbed and utilized by the body. The fibre consists of hemicelluloses, cellulose and lignin. The latter cannot be broken down by the enzymes and is voided via the rectum. Hemicelluloses are digestible fibre, but cellulose requires fermentation by microorganisms before it can be absorbed and utilized by the animal.

Energy is required to live and to work. In the young animal extra energy is required to grow. In the adult animal energy is required for reproduction; this includes oestrus, mating, pregnancy and lactation.

The main energy requirement is going to be supplied by ingestion of carbohydrate. However, some energy may be supplied from the ingestion of protein that is in excess of the animal’s protein requirement. Energy can also be supplied from a limited ingestion of fat.

In developed countries horses are often fed large amounts of so-called non-structural carbohydrates, which are mainly starch. These short feeds include corn, which is usually either oats, barley, wheat or maize, which are quickly converted by the liver to glucose. Horses, and particularly ponies and donkeys, tend to be too fat. This is poor husbandry; it compromises the animal’s welfare as it causes many easily avoidable diseases. On the other hand, working equines that would benefit from such a diet do not receive one in the developing world. The ideal diet for an equine is a high-roughage diet containing a large amount of structural carbohydrate. The problem with a high-roughage diet is that it takes time to chew, in the region of 18 h/day. Time is just what a working equine does not have. Therefore, ideally a working equine should receive a balanced diet containing a large amount of long fibre containing structural carbohydrate, with a supplement of short feed containing non-structural carbohydrate.