I'm not sure. But I use Gro 'n Win. I feed foals the "Foal Starter" pellets (a milk based pellet) starting from a few days of birth. They recommend starting them on regular Gro 'n Win at weaning (4+ months on).
Yes, my foals only get a ration balancer, it's got enough protein for growing, and mine always get fat and sassy on it. I feed Triple Crown 30% Supplement.