the microbes have to colonize to cause much harm, so even though your horses go right back to a wet muddy environment cleaning and treating with a comercial thrush killer still works. As after treatment it takes awhile for new colonies to form and start eating again. key is regularity. More the merrier. Scrub brush with warm water and concentrated lysol, pine oil, or good ole soap. (NOT BLEACH), do all four feet then squirt in your thrush buster, let things dry off a bit, then turn em loose. Do that at least every other day, it will clear up in a couple weeks. Then do it once a week as a preventive.