What is the opposite gender of doe?

The opposite gender of a doe is a buck; in some deer species people also say stag for the adult male.

Doe = female; Buck or Stag = male, depending on the animal and local usage. 

The word doe usually refers to an adult female deer. Its male partner is called a buck. In larger deer such as red deer, the male is often called a stag. For other animals, the female can also be called a doe, and the male is still called a buck, for example rabbits and goats.