I have a 25 yr old horse, who does have longer hair, and some of it is wavey too. And actually she is shedding out now to have short hair, although some of the long hair is still there. I did a power pack on her last year and she shed out great after that.
I have owned her all 25 years, and she always wanted to have longer hair at the wrong times, even when she was under lights and in a warm barn, even at 2 and 3 yrs of age. Sometimes we had to body clip her to get that nice show coat. She has absolutely no other signs of cushings. I understand that testing her now won’t give a true results, something about the fall weather or something, and that testing in late winter is the best time. also, sometimes the tests aren’t conclusive.
Also, I read somewhere that one should NOT treat a horse for cushings unless they know for sure the horse does have cushings. Right now she is getting soaked alfalfa pellets, grass hay, and pasture. She is doing fine on that and keeps good weight.