from K. Chaton:
Have you checked your horses armpits lately? How about the condition of his/her skin and coat, especially in the areas where the tack goes? It’s pretty common for horses to get dandruff or scurfing of the skin during different times of year or when they are being worked regularly and are sweating.
If you’re like me, you probably want to keep your horse as comfortable as possible. I have found that it is relatively easy to avoid having this issue crop up in the first place. Some horses can be extremely sensitive to having their skin get dry and rough especially in the girth and armpit area.
As a multiday rider I have more than one method to avoid dandruff and scurfing of the skin with my endurance horses. It’s a condition that I liken to scratches - much easier to prevent in the first place, than it is to clear up once it occurs.