Several years ago we had a grade QH type in our barn who had no more teeth and couldn’t eat all that well. After trying all kinds of feeds for elderly horses we were at our wits end. I had rabbits at the time and we took a look at the ingredients on the Purina Rabbit Chow bag and thought it was worth a try. That horse went on to eat rabbit chow almost exclusively for the next three or four years and died of a stroke at 38. He looked better on that feed than he had the previous ten years.