OK -- every time I say this, I get flak, but here I go again -- Aloe Vera Juice and Slippery Elm Bark (white/cream colour) -- it works! Vets may tell you otherwise, but I have seen it work and swear by it. It will cost you about $30 - $50 / month if you buy it at a natural health food store.
I'm so tired of getting flak for this this that I won't even go into it further, but my own vet saw it and was flabbergasted. The horse was better within 2 weeks and major improvements in a month. Try it... it's cheap and harmless -- what do you have to lose?