The ultimate farm animals, sheep are usually kept as livestock on farmland and provide three primary agricultural products of wool, meat and milk to millions of civilised human beings across the world. They are four-legged mammals who, as ruminants, are vegetarians and obtain all their nutrients from plant based foodstuffs. Sheep come in a wide variety of different breeds – some are used for their wool, some for their meat and some purely for their millk. In recent times scientists and farmers have developed special breeds to emphasise particular characteristics of the sheep to increase productivity and profitability. For example, the aptly named Polypay (meaning multiple return) is a commercial sheep breed created in the USA in the 1960’s to provide a high yield of both meat and wool.