I honestly don't feed my horse anything other than the hay she gets since she does wonderfully on it at the moment. If I start working her hard, I am probably going to have to start her on something else too, but after reading up on nutrition, I've learned that a lot of the grains out there actually aren't as healthy as they are advertised as, and the labels are not exact for several different reasons, but I know that of all the different grain mixes that are out there, sweet feed is the worst, adds more sugar than a horse needs or knows that to do with, and has almost no nutritional value what so ever. I would be picky, and say that you would like him to stay on the same stuff, and see what you can come up with. I used to mix my horses food (a different hay then that barn fed, plus her grain), and bag it up in hay bags and a little plastic baggie, and they would just grab it out of her box, and feed it to her. To me it was worth it, because I knew that she got what she needed (though in hindsight she probably could have done without the grain lol), and it made me feel better knowing that I had control over how much and what she got fed.