Will this also open the door on Zoophilia?

From a utilitarian perspective, is it any worse to live in a loving, sexual relationship with a dog or a horse [which is illegal] than to force these animals to undergo castration or neutering against their will [which is common practice]?

Interspecial relationships also exist in nature, of course.

a loving sexual relationship????? Between an animal and a person???? Yeah pets and their masters love each other but that is a owner-pet relationship, as in owner provides food and shelter pet provides loyalty and guarding. Anyone who falls in love(romantic love) with an animal needs help.

I know you're just taking the p*ss, but I'll put this out there for those who might be looking at Fido with a longing eye. Animals are not capable of giving consent to a sexual relationship with a human. Humans have too much power (worldly power and brain power) for animals to be able to relate to them on the same level.

Sexual behavior is only moral between equals. Even in BD/SM relationships, the power differentials are only possible because one party gives power to the other. When power is forcibly taken without a parties consent in a sexual relationship, that's called rape. When someone in full possession of their faculties has sex with a person who is not capable of making a rational decision (someone mentally incapacitated through illness, birth defect, or who is otherwise deficient) that is also rape. Animals cannot give consent, and physical arousal is not sufficient to imply it.

Yeah, I've probably thought about this too much.

Ummm, we EAT animals. I don't see any of them volunteering to be steak. Whats the difference?