You could try some soaked alfalfa pellets. I had to take care of a couple of older horses that could not chew hay or grain at all anymore. That is what they got everyday, along with a pellet form senior feed, neither of them where skinny. They drank the whole mixture down like soup, or should I say slop. You do want to be careful not to over feed it though. Also, always use warm water when it was cold out. Good luck.