In order to produce four or more gallons of milk each day, dairy cows have to eat a lot. Producing milk requires additional calories in the form of extra food. A large dairy cow may eat up to 150 pounds (about 68 kilograms) of grass each day, and all that munching takes time!
Cows have special stomachs, too, that make eating a slow process. Instead of having one chamber like a human’s, a cow’s stomach has four chambers. When a cow takes a bite of grass it swallows it right away without chewing it. The food goes into the first chamber of its stomach, called the rumen (animals that have such stomachs are called ruminants), where it mixes with fluid to form a soft mass. The mushy grass is regurgitated or brought back up again later, when the cow is resting. This “cud” is thoroughly chewed, swallowed, and digested as it passes through all the other chambers of the stomach. A cow spends nearly nine hours each day chewing its cud. Scientists think that when animals like cows lived in the wild they had to snatch grass in a hurry before predators attacked them. Their special stomachs allowed them to store food for later chewing and digestion once they were hidden and out of danger. Goats, sheep, camels, and antelope are other examples of ruminants.