Why do cows have four stomachs?
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Cows—mammals called ruminants—have four stomachs in order to process their low-quality diet of grass; they eat rapidly and do not completely chew much of their food before swallowing. The liquid part of their food enters what is called the reticulum first, while the solid part of their food enters what is called the rumen, where it softens. Bacteria in the rumen break the food material down as a first step in digestion. Ruminants later regurgitate the partially liquefied plant parts into their mouth, where they continue to munch it in a process known as “chewing their cud.” Cows chew their cud about six to eight times per day, spending a total of five to seven hours in rumination. The chewed cud goes directly into the other chambers of the stomach, where various microorganisms assist in further digestion. And to give their intestines time to absorb nutrients, these herbivores have a longer small intestine than most mammals.