Cows are ruminant animals, meaning their stomachs are divided into four sections. The rumen, reticulum, omasum and abomasum each have a specific role to play in digesting cellulose or plant fibre.
A cow can eat a whole day's meal in just minutes and store it in their rumen. In the rumen, the food is made into small balls of food called "cuds." Throughout the day, a cow will burp up a cud of food, chew it and swallow it again, as many as 60 times. Each time, the food is digested more. Cows spend up to eight hours chewing their cud or ruminating. The food works its way through the cow's remaining compartments and, just as in a human's stomach, digestive juices and fluids are added to it so the nutrients can be absorbed into the bloodstream.
In the cow's udder, small sacs, called alveoli, produce milk. The alveoli take the nutrients from the blood and add fat, protein and lactose (a type of sugar) to produce milk.