Cud, or Bolus, is a combination of semi-digested food and bile, which is produced by the first two chambers (the rumen and the reticulum) of the stomach of a ruminant.
The stomach of a cow, goat, sheep or antelope is insufficient on its own to break down the cellulose of plant matter, a necessary step on the way to the digestion of food such as pasture grass. The ingested material is therefore regurgitated as cud, and slowly chewed in the animal's mouth (usually while the animal is at rest) to properly combine the food and bile and to render the plant fibers digestible. The cud is then swallowed, and the latter two chambers of the stomach (the omasum and abomasum) continue the process of digestion.
