What is the singular of plural of cattle?

Cattle is a plural noun, referring to more than one. There is no particular Word for a single bovine animal.

If you wanted to refer to one animal and still use the term cattle you could say one head of cattle, but even head has a connotation of more than one. The usual method is just to call the animal by its name: cow, bull, bullock, steer, heifer, calf, or so forth.