How many chambers does a cow’s stomach have?

A cow’s stomach has four chambers. These are the rumen, reticulum, omasum, and abomasum, a digestive arrangement shared by cattle and other ruminant mammals.

The rumen is the largest chamber and acts as a fermentation vat. Microorganisms living there break down cellulose in grasses and other plant foods. The reticulum helps sort material and forms part of the pathway for regurgitated cud, which the cow chews again.

The omasum absorbs water and some nutrients. The abomasum is the chamber most similar to the simple stomach of many other mammals; it uses acids and digestive enzymes to process food and microbial protein.

“Four stomachs” is a useful shorthand but not strictly precise: a cow has one stomach divided into four compartments. Calves also have a specialized groove that directs milk toward the abomasum, allowing milk to bypass the fermentation chambers while the young animal is nursing.