Equine Digestion - By Dr. Lesely Lunn


Enzymes are protein molecules in cells which speed up chemical reactions but do not , themselves, get used up in the process.

Microorganisms are  life forms that are too small to be seen with the naked eye. They include Protozoa, Bacteria, Viruses and certain fungi and algae. The first two are involved in equine digestion.

Peristalsis is the rhythmic contractions of the alimentary canal that propel food from the mouth to the anus.

A sphincter is a ring shaped muscle which opens or closes a hollow organ.

Horses are simple stomached (monogastric) herbivores whose digestive system requires them to be trickle feeders I.e. to eat small amounts in an almost continual manner.

The digestive tract is essentially a long tube of varying diameter which begins with the mouth and ends at the anus.  It is more than32 metres long and in order to accommodate this in the body  ,the intestines loop backwards and forwards on themselves several times.

The digestive system is divided into foregut -mouth, pharynx, oesophagus, stomach and small intestine  and hindgut – -the caecum, large colon ,small colon and rectum.

The teeth, tongue, liver , pancreas and salivary glands are accessory organs in the digestive process.

The sensitive upper lip aids in grasping and moving food towards the mouth. Food is broken down into smaller particles by chewing and is moistened by saliva. Amylase, an enzyme in saliva starts digesting  carbohydrates.

Once food is chewed it starts moving down the oesophagus on the left side of the neck.(this is why your vet checks on the left when your horse is being tubed.)  The oesophagus only allows food to move one way.

The stomach of the horse is very small for his size and food moves out of it very quickly. This is why frequent feeding of small amounts ifs the best for horses. Proteins and carbohydrates are partially digested by enzymes and stomach acid. If too large a meal is ingested at one time some food will leave the stomach  without being properly digested. The cardiac sphincter is very tight and does not allow movement of food back in to the oesophagus. This is the reason that horses do not vomit.

The small intestine connects the stomach and large intestine and  most of the enzymatic digestion occurs here and food is mixed with water. Pancreatic enzymes break protein into its component amino acids most of which are absorbed in the small intestine. Bile from the liver breaks fat down into fatty acids . Starch is broken down by enzymes  to maltose which is easy to digest. The end products of carbohydrate digestion are glucose and the volatile fatty acids which are used for energy. Horses do not have gall bladders and  they become slightly jaundiced when they have not eaten for a length of time.

The large intestine comprising the caecum, large colon, small colon and rectum has about 60% of the digestive capacity and is the reason that horses are known as hind gut fermenters. The caecum, specifically, acts as a large fermentation vat in which billions of bacteria and protozoa grow and produce the enzymes that break down fibrous plant matter into volatile fatty acids. Bacterial action produces B Vitamins, Vitamin E and Vitamin K.The large intestine is the site of water absorption. Passage through the large intestine takes 36-48 hours.The small colon`s peristaltic action forms the faeces into “balls” which are delivered to the rectum where more water is reabsorbed before the faeces are passed through the anus. Healthy horses pass faeces 8 to 12 times per day. The amount, shape and consistency of the faeces are good indicators of the horse`s health.

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