How does the
digestive system
work?

The whole digestive tract of the horse has been developed to their natural foraging behavior, which is eating small portions of fibre-rich material throughout the whole day.  Under these natural circumstances, horses spend about  16 hours per day  on  grazing.  

Digestion starts already in the mouth, by reducing particle size through chewing and thereby also adding saliva to the feedstuff. The saliva, only produced while chewing, works as a lubricant for smooth passage of food, but also  helps to neutralize the acid through the presence of bicarbonate  in the stomach. In the stomach, this acid is needed to further reduce particle size, it functions as a suitable environment for digestive enzymes and besides, it eliminates undesired  micro-organisms that entered the intestinal tract together with the feed.  

After passing through the stomach, the feedstuff enters the small intestines. At the beginning of the small intestines,  digestive fluids are added. Fluids from the pancreas reduce protein and carbohydrates, and bile salts from the liver reduce fat. Contradictory  to humans, horses do not have a gall bladder, so bile salts are directly added from the liver. When proteins, carbohydrates and fats are split, they can be  absorbed through the wall of the small intestine. Furthermore, the soluble  fibres  from the feed serve as fuel for the desired microbes in the intestines.  

After passage through the small intestine, the food enters the large intestine and caecum, where the most important digestive process takes place. The for the horse  indigestible,  fibre-rich feed material is converted into a digestible form through  fermentation, which is done by bacteria. This digestible form can be absorbed by the horse. The horse obtains most if its energy (about 90%) from fibre-rich food.