When my Cody was young (11 mos to 2 yrs.) I used Triple Crown Jr. Or whatever their feed for youngsters is, plus as much grass hay as he could eat. He stayed in good weight through all the growth spurts. Now he is 4 1/2 and I love Strategy by Purina. He gets maybe a lb. Morning and night, loves it, plus all the grass hay (orchard/bermuda) he can eat and he maintains very nicely.
From what I've learned with drafts you need to stay away from alfalfa and "grain" do a low starch diet, up the fats in their diet by actually giving them 1 cup per 1000 lbs. Of pretty much any kind of oil over their food. This is to prevent muscle issues some drafts have. Check out "Draft Horse Resource Index" at draftresource.com and there is a section on feeding drafts and people who are really knowledgeable about them.
Your Ben looks good. Looks like you got another girth?