Stunted growth due to illness buck

[myheaven]

My registered buck ended up with joint ill which in turn messed up his rumen which then stunted his growth. After many vet visits later and lots of time kayopectate and fuss later, his rumen is back to normal. With rumen screwing his growth how can I beef him up the fastest? I do not use soy so that's out. I have alfalfa pellets. I have started him on just a little of that, I also have oats, distillers grain, and corn. On top of heifer/ grass hay. I need him to breed in two months and umm he's so small! My 12 week old buck is starting to look bigger.
My girls are going to look at him and laugh till they die!