CUD' CUD is an acronym for Cud Chewing, which is a type of behavior exhibited by animals such as cows, sheep, and goats. It involves the animal repeatedly moving its lower jaw from side to side in order to grind down food that has already been partially digested in the RUMEN, which is the first chamber of the stomach. This behavior helps the animal to extract more nutrients from the food and is an important part of their digestive process.