The digestive system in animals is a major system. Its function is to convert food that is ingested into fuel for the body and eliminate the waste. The structure and process varies from animal to animal. The digestive tract of grazing animals differ greatly from that of omnivores and carnivores.
Grazing animals have either the most complex digestive system as with cows or the most primitive as with horses.
The mouth of grazing animals accommodate the feeding on grasses. They have tearing incisors, a gum bar instead of canine teeth and grinding molars. The .prey animals have large dagger like canine teeth for ripping into the flesh and their incisors have evolved to grip and hold. Rodents have enlarged incisors for gnawing.
The saliva of grazing animals is rich in minerals to initiate the digestion of starches. Prey animals do not keep their food in their mouth but swallow large chunks of meat to begin the digestive process in their stomachs.
All animals have a pharynx, a tube that accommodates both respiration and digestion. At the junction of the trachea and the esophagus is the bronchial tube acting much like a valve allowing air to flow through the trachea and food to continue down the esophagus. This is where the digestion of grazing animals depart. The cow has a very involved sytem.
Once a cow swallows its food it enters the rumen the first of four chambers where the plant matter is broken down. It is then passed to the oesophagus which allows the partially digested vegetation to regurgitate back to the mouth where it chewed. It is known as cud. Once the cud is thoroughly mixed with the saliva it is swallowed again and enters the reticulorumen where any undigested food is combined with friendly bacteria to complete the breakdown. It then passes to the omasum where any liquid is assimilated into the body and pumps the digested food to the true stomach called the abomasum where acid digestion takes place. From there it enters the small intestines, the main digestive center of the animal. Then to the duodenum where the food is mixed with the endocrine enzymes. The jejunum is the next stop in this complicated process here the sugars of the digested food is absorbed. The caecum connects the illium, which continues by absorbing the proteins and the large intestines. It stores the undigested food and further breaks down cellulose. The large intestine absorbs vitamins and pushes the waste into the rectum where it leaves the body at the anus.
The horse’s digestive system is the most primitive of the grazing animals they have what is known as a one way digestive tract which means they cannot regurgitate their food. This results in a tendency for colic.
Omnivores and carnivores swallow their food into their stomachs, digest it, and eliminate the waste.
Milwaukee area residence can find more detailed information about the digestive system of animals at the Milwaukee Public Museum the Milwaukee Public Library and at the Milwaukee County Zoo.