If you read Starting Strength, you'd know. To summarize, it has everything baby calves need to grow strong, which is also similar to what humans need to grow strong. Lots of protein, along with some sugar and lots of vitamins and minerals.
I might add, if the lactose gives you grief, invest in some kefir grains and ferment it out. You get some extra b vitamins and folate in the exchange. Plus it's hella tasty.
