Ninjaedit: I understand the concern, but I already have this all typed up - and there's no way I've soiled my search history this way without having something to show for it. For what it's worth, I tried to stay as tasteful as possible.
It depends. But before we proceed, let me ask you: Are you really prepared to do quantitative interspecies penile comparatistics?
I was born ready.
Okay, let me dive in then.
Toady, if you read this: I hope I'm not crossing any lines here - I'll try to keep it as clean and detached as possible.First off, I guess we should clarify what kinds of animals we're talking about. For example, I'll be excluding cats and some dog breeds as well as gerbils and the like for being too small. Mostly I'll talk about horses and various larger dog breeds. The various bigger farm animals are left as an exercise to the reader. Data on intercourse with these species would be especially welcome since the relationship between a rural lifestyle and bestiality is currently unclear.
This Straight Dope column may serve as a starting point for further reading on the prevalence of zoophilia and bestiality in the general populace.
First off, horses! We already had an example earlier off a horse shlong, so I guess we won't need any more evidence of hung like a horse being a compliment. Given that mares are designed to withstand intrusion by those things, you'd have to need three-legged trousers to consider man-on-horse intercourse to be painful for the animal.
Moving on to dog breeds, we get into more interesting territory. I'll restrict myself to looking at length, but note that girth is similarly important here.
First, we have to ask ourselves: How big is a human dick? Naturally there is a
Wikipedia article on the subject. Average size apparently is around 13 cm.
Sadly (?) data on the average penis size of various dog breeds is
harder to come by.
This chart suggests that at least some dog breeds pack more of a punch than even well-endowed human males, so I guess we can safely assume that the females of said breeds are at least in principle equipped for interspecies intercourse.
This manual (!) appears to agree without going into details, but we must consider the possibility this may be a biased source.
Even if no currently existing breeds fit the bill, you could always apply selective breeding to attain the characteristics you desire. It is currently
unclear whether such attempts have already been made.
In closing, I'd like to remark that pigs have
huge penises. Next time someone calls me out for my table manners, I'll make sure to mention this fact.