Digestive
Introduction
Unlike humans, horses digest part of their food by fermentation in the huge large intestine. This is because they are herbivores and must digest large amounts of plant matter.
Horse’s chew their food with lateral, side to side, movement of the lower jaw which allows the rows of cheek teeth, molars and premolars, to grind food. The tongue then pushes the food material to the pharynx where it is swallowed and passes into the oesophagus.
The oesophagus is made up of skeletal and smooth muscle and connects the pharynx to the stomach. There are sphincters within the oesophagus that open to allow food to pass, however, prevent it moving back towards the pharynx.
Food material enters the stomach from the oesophagus through a one-way valve that prevents food moving back into the oesophagus, hence the reason horses are unable to vomit. From the stomach material passes through another valve and into the small intestine. Here the food material is broken down into they key elements, fat, protein and carbohydrate and is absorbed into the blood. The food material then passes into the large intestine (caecum and large colon) where cellulose is broken down by the bacteria present. The large intestine has to fold within the abdomen due to its size. One of these folds, the pelvic flexure, is a common site for impactions to form. From the large intestine waste material is passed to the rectum and excreted.
Waves of muscle contractions, peristalsis, allow the flow of food material through the digestive system.
The liver is an accessory gland of the digestive system and is the largest gland in the horse’s body.