The truth is that there is no noun in general use that refers equally to a cow or a bull.
Zoologists use two terms. The first is ‘ox’, which is often restricted to animals of the genus Bos (i.e. the wild cattle – gaur, banteng, yak, aurochs, and kouprey – as well as domestic cattle). In popular use, though, the word ‘ox’ often refers to a castrated male animal, so that isn’t a perfect solution. The second zoological term is ‘bovine’, which is used as a noun to refer to any animal of the wider group that comprises cattle, buffaloes, and bison. But this would be a strange choice in most general contexts.