A number of dairy herds are kept in barns or sheds for most of their lives and are given feed that has been especially made for them. This feed contains grain like corn, hay including grass and alfalfa or clover, and fermented chopped feed called silage that is usually made from corn, wheat or barley. Cows are often kept in stalls where they have enough room to lay down comfortably. Such large dairies must supply straw or saw dust for the cows to rest on without getting sore from the hard concrete floor.