03-28-2018, 08:10 PM
Bearing in mind the proposal was for just a day or so, and most of the time male animals spend waiting around for -someone- to go into estrus, I would have to say:
Draft horse stallion, on some farm with my own field (so I don't have to whup-ass some other horse), with females provided by humans for natural service.
I have some reservation with being a dog; male dogs always seem to have a sort of awkward look on their faces after they tie.
I also wouldn't mind standing in for a boar hog, or a jack donkey.