tends to live in woody-cellulose  products-      wood bunks,    old dead tree stumps in their pen,   even  piled up  ricks of manure holds it-  basically anything they rub on...
    I've had decent luck  using  diesel fuel/iodine mix to   spot treat patches  early.    It takes  about  2-3 weeks to see   new hair to re appear.

When the hair is about to change for summer heat,  might as well  let mother nature  do it for you.. as  sunlight and heat will kill it too.