Why do cows have a tail?

Many animals have tails, and different animals have tails for different reasons.

They can be used for locomotion, balance, steering like a rudder on a boat, giving a push against something to gain propulsion, hanging from, grasping food or branches, sitting back on (curled up), swatting flies - or people, warnings (rattles on a snake's tail), showing affection (cat wrapping its tail around your leg), communication (beavers hitting logs, cats' tail angles), swimming, and a lot more.

For example, the male peacock's beautiful open tail is used as a sign of mating readiness. Dogs and cats use their tails as one sign of emotion and communication. Birds use their tails to stay balanced when not moving.