Some horses will eat anything, especially if it's got a salty taste (hence the dog food being so popular with Sara's pony.) My mom had a trail horse who would refuse to budge if he heard her rustling around on his back with a food-like substance until she offered some to him. He even at a bologna sandwich one day.
Of course, just because they'll eat it doesn't mean you ought to feed it to them. Horses are not designed to consume meat. Then again, there are those who'd argue that hot dogs are not meat