Answer:
Mature, intact male cattle that are used for breeding cows and heifers are called bulls.
Intact male cattle that are almost, of or past weaning age but are younger than 2 years of age are called bullocks. ('Bullock' may also be a European term for a steer, according to the Canadian Oxford Dictionary.)
Male cattle that are castrated before reaching puberty are called steers.
Male cattle that are castrated after puberty are called stags.
Note that there is no such thing as a "male cow." A cow is only female, never both or either or.