This sentence is translated to be a general statement: horses are big animals.
I have seen a few comments indicating that होता (hota) is used as a general term, ie. चुहे काले होते हैं - Rats are black.
Why doesn't this sentence translate to "the horses are big animals" since होवे is not included in this sentence?
I think चूहे काले हैं । can mean both 'Rats are black' (generic) and 'the rats are black' (specific), although I am not very good at using होता (hota) yet... I queried this answer before, because, like you, I think this translation is inconsistent with the one before.