The term “antonym of cow” is a bit tricky as nouns like “cow” don't typically have true antonyms in the traditional sense.
A cow is a specific type of animal, a female bovine. If we were to stretch and look for something that might be considered in opposition in some way, we could perhaps mention “bull” as the male counterpart. However, this is not a true antonym as an antonym usually implies an opposite in meaning rather than just a different gender.
Another way to approach this might be to think in terms of characteristics. For example, a cow is docile and gentle. So, an animal that is fierce and aggressive, like a tiger or a lion, could be seen as contrasting with a cow, but again, this is not a proper antonym.
In conclusion, it's difficult to find a true antonym for “cow” as it is a specific noun that doesn't have a direct opposite in the way that adjectives or verbs might.