Have you ever heard of the product HS-35? Absolutely wonderful horse supplement. I would definately put this horse on it. It's great you're adding biotin but that alone will not do it. You need a balance of trace minerals also. The forms of minerals are most important too. This supplement contains proteinate forms of zinc, copper & manganese which are the best you can buy. It's hard to find a supplement with this quality in forms you know the horse can utilize. I don't know if HS-35 is available in your area, but from the brochure I have on it, you could contact
faye@hs35.net or call 1-888-875-2425.