In this sentence both subject and predicate are nouns. In situation like this the word це is often used to avoid ambiguity and to make clear that it is a sentence and not just a strange combination of two nouns. The word before це is a subject.
I would like to add that when there is a word це before predicate there should be a dash before це, for some reason it was neglected here
Корова is singular and so is тварина. So the translation must be A cow is An animal.