Dump the sweet feed. I like to feed my youngsters on Purina Equine Junior until they're about 2 years old. If your horse is stunted, then I'd keep him on it longer. If he wasn't underfed for too long, he'll catch up, it'll just take him some time. Due to problems with OCD and other joint issues, I won't feed mine over 16% protein. It's plenty to feed them for growth, and not so much they grow so fast that it causes joint issues. If you're not a Purina fan, Nutrena, Triple Crown, Buckeye are other names of good feeds that I can think of right off the top of my head.