Sheep have always been very popular in the Bible - Isaiah reflects this when he states "all we like sheep .."!
Sheep were also a valuable commodity and were often taken as plunder in wars.
Israel are once recorded as taking six hundred and seventy-five thousand sheep from the Midianites in one go.
Sheep need a shepherd and many a prophet or king has earned a crust looking after the flocks of another (e.g. David, Amos).
Symbolically, God's people (Israel, or the Church) are often referred to as sheep, and Jesus is the good shepherd who lays down his life for his flock.