I would go out and look into wither mare and foal feed (it can be fed up to 2 years of age and sometimes even older). Either find something that is already fortified with vitamin and minerals or buy an additional vitamin and mineral supplement. I like the purina feeds, especially the strategy and omolene lines. These are fortified feeds and you do not have to feed all that extra vit and min supplement. Try to go for something 16% protein and around 6% fat or maybe even a little higher.
On the other hand to all the people who think that cow hocked horses will always be cow hocked when they get older. Every single baby I have ever owned has been cow hocked at least a little, but if it is not severe it can be corrected at young ages with proper hoof trimming and proper muscling. Very rarely do do I ever see a yearling that has the proper muscle tone unless someone is longeing them everyday and building the proper muscle needed to correct small conformation problems. The same thing goes for horses that are slightly toe out! A lot of people do not understand how important muscling is on their horse, it can correct minor confirmational problems and it makes them look like a completely different horse!
You know how to make a miniature horse even smaller? Leave them in the dryer a little longer!
"Don't ever regret something that once made you smile"