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How does a bovid’s four-chambered stomach digest tough plant material?

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An American bison, or plains buffalo (Bison bison), stands in tall yellow grass with open plains in the background. — bovid American bison, or plains buffalo (*Bison bison*).

It is a common misconception that bovids have four separate stomachs; rather, they possess a single stomach divided into four distinct compartments: the rumen, reticulum, omasum, and abomasum.1

Because bovids cannot produce the enzymes necessary to break down cellulose, they rely on a specialized digestive process:2

Fermentation: Ingested plant material enters the rumen, which acts as a fermentation vat. Microorganisms break down cellulose into fatty acids that provide the animal with energy.31
Regurgitation: The animal regurgitates the partially fermented material, known as cud, to chew it again. This mechanical breakdown increases the surface area for further microbial action.23
Processing: The reticulum assists in mixing, while the omasum absorbs water and nutrients.1
True Digestion: Finally, the abomasum—the "true stomach"—uses acid and enzymes to digest proteins, similar to the process in nonruminant animals, before the material moves to the small intestine.1