Homosexuality amongst "animals" is too ridiculous to even discuss in this context.
Anyone who has ever had anything to do with rearing livestock will understand why. Animals mate by instinct, they are also given natural signals at the appropriate times by the appropriate gender.


Very occasionally when under extreme stress, as in being herded or sent to market some animals may go through the action of "mounting" one another, getting into the position for mating, but I have never known penetrative mating to take place.
This behaviour seems to be triggered by anxiety.