Why do cows have four stomachs?
Cows have one stomach with four compartments: the rumen, reticulum, omasum and abomasum. This system lets them digest tough grass and plants that humans cannot.
Grass contains cellulose, a tough material that most animals cannot break down. In the rumen, the largest compartment, which can hold about 150 liters, billions of bacteria and other microbes ferment the plant material. The reticulum helps sort food and forms it into soft lumps called cud.
Cows bring up the cud and chew it again, a process called rumination, which can take up to eight hours a day. When swallowed again, the food passes to the omasum, which absorbs water and nutrients, and then to the abomasum, the true stomach, which digests food with acids and enzymes much like a human stomach.
Other ruminants
Sheep, goats, deer, giraffes and buffalo are also ruminants with similar stomachs. The microbes in their rumen produce methane, a greenhouse gas that cows release mainly by burping. Scientists are testing feed additives, such as seaweed, to reduce these emissions.
Did You Know?
A dairy cow can drink about 100 to 150 liters of water a day, roughly a bathtub full.