I think horses are similar to us in the idea that everyone of us has a different metabolism, because horses do too. I have seen horses that live for 40 years eating straight alfalfa, and horses live 40 years eating grass out of a pasture. Personally, I've fed orchard/timothy mix, orchard/rye/oat mix, three way hay (oat, wheat, pasture grass), alfalfa/orchard mix, straight alfalfa, pasture grass, and bermuda. I have found that like others have said, orchard/timothy, first or second cutting, is really the best. I like rye mix if you can get the horse to eat it, and 3 way is another hay that is pretty good for most horses.