Horse leg hair is falling out?

[Traveller02]

Hi, I have a 30 year old retired Quarter Horse/ Morgan cross who has a crazy thick winter coat that sheds out weird every spring...( Vet ran a whole bunch of blood work last season and she has no health issues and does not have Cushing's disease. ) She is getting now just getting over mud fever that she gets every spring because of the mud... But this is the first time she is losing the hair behind all 4. of her legs. Their is noscabs when the hair comes off-( it's comes off in clumps. ) She doesn't act like it hurts her and she is not itchy... When the hair falls out in clumps there is a whole bunch of new smooth "baby". Underneath. It's only on the back of her legs from the pasterns up to her "armpits". She does have very very thick hair on her legs... Should I be concerned? Does it have something to do with her shedding out her coat for the spring?? Is it normal?? Does it have to do with the mud fever??

Any help will be greatly appreciated!
Thank you.

 

[eggs]

Had something's no similar with my old mare. Coming out of winter I could rub my hand up and down the back of her cannons and small clumps of hair would come out especially on her fronts. Never seemed to cause a problem.