Why do some animals chew their cud?

Animals like cow, buffalo, sheep, goat and camel have the habit of swallowing their food first and later bringing it back into the mouth to chew it at leisure. Such animals are called ‘ruminants’ or ‘cud-chewing’ animals. Thousands of years ago, these animals could not protect themselves against their aggressive enemies like, the lion and the tiger. In order to survive, they would swallow their food quickly without chewing it and run to a safe place, where they would chew their food at leisure. But, what makes such a strange process possible? The cud-chewing animals have a peculiar digestive system. Their stomach has four compartments — (i) Paunch or rumen (ii) Reticulum or honeycomb bag, (iii) Omasum or many plies, and (iv) Abomasum or the true stomach. When the animals swallow food, it goes into the first chamber. This is the largest of the four compartments. At this stage food is in the form of coarse pellet, that is the unchewed portion of food. In this compartment, it is softened and moistened. From here it goes to the second compartment, where it is converted into small pieces of convenient sizes called ‘cud’. At the time of chewing, the cud comes back to the mouth through a process called ‘regurgitation’. After it is chewed, it goes into the third compartment. From here, it passes on to the stomach where digestion takes place. Unlike other ruminants, camels do not have the third compartment. Cows, sheep and goats do not have any teeth in the upper jaw. Instead, the gums form a tough pad. So, with the help of the lower teeth and this pad these animals graze and chew the food.