I have been told to use Copper Sulfate mixed with Stockholm Tar and apply that to the bottom of the hoof every day, I have seen it work very well though I have never used it myself.
For my big boy, I spray Stock Iodine (that we spray on umbilical cords of calves) onto his hooves and that worked a treat, he used to abscess really bad and this winter *touchwood* I have had no abscesses at all. I make sure to only get it on the bottom of his hooves, I don't bring it up the wall at all or near the coronet band. And I stand him either on concrete, or some other dry surface until his hooves are dry with iodine
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms