Sheep have been kept as agricultural farm animals for centuries and provide meat, skin and wool. As herbivores and ruminants they graze and chew the cud by turns. Because there are hundreds of sheep breeds, these mammals can differ considerably as far as their fur and size is concerned. Sheep weigh between 45 and 180 kilograms and can reach ten to twenty years of age. They compensate for their impaired spatial eyesight with an excellent sense of hearing and a very sensitive sense of smell. In a flock, sheep mostly follow the instructions of a shepherd. However, they have their own hierarchy as well.