Domestic sheep (Ovis aries) are ruminant mammals typically kept as livestock.
Although the name "sheep" applies to many species, in everyday usage it almost always refers to Ovis aries.
Domestic sheep are the most numerous species in their genus, numbering a little over 1 billion.
They are most likely descended from the wild mouflon of Europe and Asia.
They were one of the earliest animals to be domesticated for agricultural purposes.
Sheep are raised for fleece, meat (lamb or mutton) and milk.
Sheep's wool is the most widely used of any animal, and is usually harvested by shearing.
There are about 5.5 m people on the island of Ireland and about 7 m sheep.
Reference: http://en.wikipedia.org/wiki/Sheep