Anyone familiar with cows knows that when they are not actively eating they are usually contentedly munching their cuds, a process that is apparently not only pleasurable but also essential to the health of the animal.
The cow’s stomach is divided into four compartments, but the statement that the cow has four complete stomachs is not true, strictly speaking. When cows eat grass or other food, they chew it only enough to enable them to swallow it.
The food passes first into the front division of the stomach, called the rumen or paunch, which is simply a storage place. From the rumen, it gradually passes into the second stomach division, where it is compacted into small masses or cuds. When the cow is resting, the cuds are regurgitated one by one, thoroughly chewed and mixed with saliva.
When the cows swallow the cud, it goes by the way of the valve in the throat to the third division of the stomach where the digestion begins. The fourth stomach division plus the intestine complete the digestive process.
Other animals that chew a cud include deer, sheep, goats, giraffes, and antelopes. Animals of this type are called ruminants because the first part of the stomach is the rumen.