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Why are deer classified as ruminants?

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male white-tailed deer — deer Male white-tailed deer (*Odocoileus virginianus*).

Deer are classified as ruminants because they belong to the suborder Ruminantia, a group of mammals characterized by a specialized, multichambered stomach that allows them to process plant material efficiently.12

Because deer do not produce the enzymes necessary to break down cellulose found in plants, they rely on a sequential digestive process. They store ingested food in the first chamber, the rumen, where it softens. They later regurgitate this material, known as cud, to chew it again, further breaking down the tough plant fibers.13

After being re-swallowed, the food passes through the remaining stomach chambers—the reticulum, omasum, and abomasum—where it is further digested with the help of essential microorganisms. This complex system enables deer to extract nutrients from their diet, which is vital for their high metabolic demands, such as the growth of antlers.134