One could make an argument for the fox-horse race based on the fact that people riding horses hunt foxes.

I have only seen racing pigs at a county fair. It was hilarious. There were four pot-bellied pigs with colored sashes around their mid-sections and the green one came in last because he had to pause and poop in the middle of the race. And I think at one point he stopped and went the other way, just because he felt like it. All in all, it was a quality way to spend part of my afternoon.