What is a name for an adult calf?

First of all, there is no such thing as an adult calf. A calf is no longer a calf after he/she is weaned. After a calf is weaned, she would be called a heifer. If it's a male, then he would be called a steer (if he's already been castrated) or a bull (if still intact or uncastrated). A heifer becomes a cow after she has had at least two calves. When she has her first calf, she is commonly referred to as a first-calf heifer.