I get how "Cows eat grass." and "Cows don't eat carrion." are generally true statements about cows. However "Cows are not cats." seems different to me since it is not information about cows. it is sort of nonsense, while the other two statements could be informative, say, to a child. If बिल्लियाँ could be understood as "felines", I could understand this sentence as "a general truth." Perhaps a child would not know the word "feline", but I think it would be more natural to say "A cow is not in the cat family." But that seems too obvious state. Hindi speakers, to your mind is this a good example of the use/meaning of होता है?
Hindi does not have a definite article that's equivalent to 'the'. If you really want to specify definiteness, you can use यह/वह (this/that) but otherwise, definiteness is inferred from context. So, for most sentences, you can translate into English with or without the 'the'.
But because this sentence has a 'होती', this is a general statement about all cows and not a particular set of cows. Therefore, using 'the' isn't appropriate.