My 14 yr old mare has been losing a lot of hair. It's not rain rot and it's way more than just slicking down for the summer. At 1st we thought it was from the dominant mare biting her....but it's all over her body. Patches are missing from her shoulders, neck, stomach, legs and hind area. There doesn't seem to be any irritation on the bald spots. You can also pinch 2 fingers 2gether & pull out a tuft of hair (roots & all) without bothering her and very easily. Does anyone have any idea what could be causing this? Or how to treat it?