You have to be careful with ponies, as they can easily get overweight. I'm not sure about the BOSS, but the vegetable oil will add fat to his diet nicely. I would also switch his feed to a feed that is formulated for growing babies, like Purina's Equine Junior. I have used it alone with great success. It is a complete feed, so there is no need to supplement it with Vit/Min. Just feed/hay/water. The Purina feeds are also concentrated so it doesn't take as many pounds of feed per pounds of body weight.