Animals get food and energy from plants or from animals that eat plants directly or indirectly. However animals differ greatly in their needs. Each kind of animal has its own particular needs and each must have a certain amount of the right kind of food.
A large range area is needed to give sheep enough grass. Sheep aet grass right down to the roots and time must be allowed for grass to grow back where they have grazed. Thus they must be moved to order grazing areas fairly often. Goats also eat grass.
Cattle need grass, hay and grain for their food. But they also feed other kinds of food.
The best broiler breed is well-known for its white feathers, yellow skin and fast growth. It grows well and needs a relatively small amount of food. Broiler chicks are fed a mash mixed of ground corn, meat meal, fish meal, soybean meal, minerals and vitamins. With 7 pounds of this food a farmer can raise a 3 pound crossbred broiler. There is no animal other than chicken so efficient in producing meat.