The correct name for adult male cattle is "bull." Technically, the term "cow" refers only to an adult female cattle. "Calf" is the correct term for baby cattle, regardless of gender.
"Bullock" is a term used for a specific sect of male cows, but its exact meaning can vary amongst different types of English. In British English, "bullock" refers to a bull that has been castrated and is no longer able to reproduce. In North American English, "bullock" refers to a young bull (generally under the age of two) that has not been castrated and can still produce offspring.