Well, you can't really blame blogtown, since the original video hillbilly claimed the horse's butt itched. But it's actually been scientifically observed that horses masturbate against trees, and unless you just happen to be privy to this "special" information, I can see how it might be mistaken for butt-itching.
Hmmm...someone's been googling "painful rectal itch." Now we know why WSH has been spending less time sitting in his office and more time hanging out in the the hall in his underpants.
That is a female horse, and she is masturbating.