Cud is a portion of food that returns from a ruminants stomach to the mouth to be chewed for the second time. It is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant, produced during the physical digestive process of rumination. Ruminants, such as cattle, giraffes, goats, sheep, alpacas, and antelope, are unable to produce the enzymes required to break down the cellulose and hemicellulose of plant matter. Accordingly, these animals rely on a symbiotic relationship with a wide range of microbes, which largely reside in the reticulorumen, and which are able to synthesize the requisite enzymes. When the stomach content, or the cud, arrives in the mouth of the ruminant, it is pushed against the palate with the tongue to remove excess liquid, the latter is swallowed, and the solid material is chewed thoroughly so the cattle can extract the minerals present in the cud brought to the surface during rumination.
Cows chew their cud because they are ruminants, meaning that part of their stomach, the rumen, is like a large fermentation vat. It contains bacteria that digest the cow’s feed and convert it into energy and protein. This softened food is called the cud, and it is sent back up to the cow’s mouth, where it is re-chewed before going back down into her stomach to be fully digested. Chewing cud produces saliva, which is important for controlling rumen acidity. Too much acid hinders the growth and function of the rumen bacteria, especially those that digest fiber. Cows need to be comfortable and relaxed to chew their cud, and usually lie down to do it. They can lie down for very long periods of time, not to sleep, but just to chew their cud. Cud-chewing cows are generally healthier. With a well-functioning rumen, cows will digest more of their diet and produce more milk.
