The horse is a non-ruminant herbivore. Non-ruminant refers to animals with only one stomach, compared to a ruminant animal (e.g. cattle), who have multiple stomachs in their digestive system. The horse being a herbivore, lives on a diet of plant material.
Looking at the equine digestive system in its completeness, we are faced with some unique factors that we need to take into consideration, when choosing the right feed for the horse.
Digestion and physiology in a horse relates to 4 key parts of the body – the mouth, stomach, small intestine and large intestine. Digestion starts at the mouth, progresses to the stomach, then the small intestine and finally the large intestine before it leaves the body.
Digestion can either be physical or chemical. Physical digestion involves the breakdown of food through force, for example, grinding, mixing and turning, whereas chemical digestion is the breakdown of feed with acids and enzymes in the stomach and small intestine.
Digestion in a horse starts in the mouth. This is where the initial physical digestion occurs. It starts with the teeth through chewing or what’s referred to as mastication. Horses have a full set of teeth and both an upper and lower jaw. Many other species do not have a combination of an upper and lower jaw which makes the horse a little bit unique. Horses have incisors at the front, designed for biting and cutting grass and leaves, and they have a large set of molars at the back of their mouth designed specifically for grinding. When horses chew, they don’t chew in an up and down fashion like humans, they grind their food in a three-way motion – up and down, side to side and backwards and forwards in what we call an occlusal pattern.
Saliva is produced in the mouth which is designed to moisten the food bolus. The bolus is formed when a horse chews up its food and then mixes it all up into a ball. If the bolus is too dry it is very difficult to pass down through the oesophagus (or throat) into the stomach. Horses unfortunately cannot regurgitate, they have only a one-way movement of feed down their oesophagus so if anything gets stuck, they can’t push it back up like humans. They must somehow force it down. So, the bolus must be lubricated.
When horses chew fibre, they produce a lot of saliva, primarily from the parotid gland at the back of the mouth. We are able to influence the amount of chewing the horse does and with that increase the production of saliva up to ten times, by feeding a high fibre diet. One of the ways horse’s select their feed is through taste, which also occurs in the mouth.