Ruminants are herbivorous mammals like cow, goat, buffalo, etc. that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. Ruminant stomachs have four compartments: the rumen, the reticulum, the omasum and the abomasum. Rumination is a process in which the grass-eating animals bring the previously consumed food into the mouth once again and chew it.

Ruminants are the grass or plant-eating animals. Their stomach has four chambers, i.e., rumen, reticulum, omasum, abomasum. The partially digested food from the reticulum returns to the mouth to be chewed again. This partially digested or semi-digested food is called the cud.