
Is this a serious question? If it is I shall answer seriously. Yes. Cows have testicles. There are two genders in cows. Male and Female. The males have testicles. There are many dishes around the world where they use cow testicles as the main ingredient.
Now if this was not serious, I don’t understand the joke.

are you stupid?
bulls are still cows, MALE cows
it's not like bulls are a completely different race from cows
like in german there is a different word for a male cat like with cows and bulls but in the end it's still a cat
Cows have testicles?