Cattle are large grazing animals with two-toed or cloven hooves and a four-chambered stomach. This stomach is an adaptation to help digest tough grasses. Cattle can be horned or polled (or hornless), depending on the breed. The horns come out on either side of the head above the ears and are a simple shape, usually curved upwards but sometimes down. Cattle usually stay together in groups called "herds". One male, called a "bull" will usually have a number of "cows" in a herd as his harem. The cows usually give birth to one "calf" a year, though twins are also known to be born. The "calves" have long strong legs and can walk a few minutes after they are born, so they can follow the herd.