If you put on him on a senior feed it should help. You need to be careful with vitamins and minerals , it dependes where you live, and what the hay /feed is like. Try googling 'Understanding Vitamins and minerals for horses " . You may get some decent articles. Biotin supplement for his hooves. It takes A Year for a hoof to grow out. His hooves should improve, it will just be time consuming. As he gains weight his overall health etc will be improving. I would be concerned with the roaring, and have him Vet checked on that to see if it does affect his breathing . Good luck .