I'd always heard about the horse hair. It really seems bizarre that they would have used it. I know that 'back in the day' they tried not to waste anything usable but who in the heck ever came up with the concept of adding it into plaster? - Must have been a real b*tch during the winters for them ponies! LOL!
The only horses I own are beneath the hoods of my Mopars but I do have a couple of cats. I don't think they'd be too fond of the idea.