If possible, I would try and make sure that he has hay available as much of the day as possible. That will definitely help, as horses systems are made to have small amounts of food all day long. Is alfa beet like beet pulp? That should help if so. His nutrient intake from the hay depends on how much he gets, what type(s) he gets, and how good of quality it is. I would at least make sure that he has a salt block, or as others have mentioned on here, loose minerals. You can also add some grow colt, or some other similar supplement into his feed, which is said to help growing babies, but I personally have never tried it, so can't really give you an opinion on whether or not it works, or is worth it. I think that as long as he keeps looking healthy I wouldn't worry about changing things.