A herd is a group of animals that live and travel together, usually for protection. The most common type of herd is composed of cattle, which includes COWS, steers, BISON, and HEIFERS. COWS are female cattle that have had at least one calf, while steers are male cattle that have been castrated. BISON are large, shaggy-haired mammals that are native to North America, and HEIFERS are young female cattle that have not yet had a calf. All of these animals are members of the same herd.