"When children see animals in a circus, they learn that animals exist for our amusement. Quite apart from the cruelty involved in training and confining these animals, the whole idea that we should enjoy the humiliating spectacle of an elephant or lion made to perform circus tricks shows a lack of respect for the animals as individuals" – Peter Singer from the book Animal Liberation (I think)
Asking an elephant to stand on its hind legs or to sit is an affront to respect but Australian philosopher Peter Singer is A-OK with people having sex with animals* so long as the animal isn't harmed. Although it isn't mentioned, I will assume that he also demands those having sex with their pets respect them in the morning.
*in an article titled "Heavy Petting"