Tail goes bald,whiteblaze falls out every spring last 5 yrs, after to diff state

Hi BBT,
Yes, alopecia areata can be worse during the warm seasons and like most autoimmune diseases can be quite variable in presentation. I don’t see anything in your post that rules out alopecia areata and some things that suggests it, beside the seasonality the distribution is typical. I would like to know what other diagnosis’ you have received and the results from the biopsies. What type test was run that was positive for aa.
DrO
Ps:
1) What city and state do you live in.
2) For more on Se and Vit E see https://horseadvice.com/horse-equine/horse-care/nutrition-feeds-feeding/selenium-and-horses/
3) Insect bite hypersensitivity still remains on my list see https://horseadvice.com/horse-equine/diseases/skin-diseases-wounds-and-swellings/hair-and-coat-problems-itching-irritated-skin/culicoides-hypersensitivity-sweet-queensland-itch/