I have been mixing Captan (an agricultural fungicide) into zinc oxide and applying to clipped legs twice a week with great results. Last year (first year retired on pasture board) my 26 yo gelding with four white legs was a mess. Scratches all up his legs to the knee and funky, scratches like mess, on his rump…
My vet suggested Captan as an “old school” method. I have mixed captan with water in spray bottle to spray legs, sprinkled it on directly to top line, and this year mixed it into zinc oxide. And this season he only has a few small scabs that fall off after application.