Why do cows have four compartments in their stomachs?

Answer 1

A cow's diet of coarse plant material like grass is much harder to digest than that of an omnivore's or carnivore's diet. Thus it requires several steps in order for a cow (being a ruminant) to fully digest and absorb the nutrients from the plant matter that she eats. A simple stomach that secretes hydrochloric acid and peptidases just doesn't cut the mustard when it comes to having to digest a 100% forage/roughage diet. An animal, like humans, with only a simple stomach with no cecum would starve to death on coarse roughage like dried grasses and hay. Thus, a ruminant is more adapt and efficient at breaking down and utilizing the nutrients from such fodder sources as grass, clover, alfalfa, or even leaves from trees. The multiple chambers and the ability to regurgitate and rechew partly digested matter make it all the easier for that animal to efficiently digest and use the nutrients from the grass a bovine eats.