Cattle are large grass-eating mammals .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.