if it looks "shaved" your dog is most likely gnawing at its legs.... my Shelby does this once and a while, in fact i posted about something like this about a year and a half or so ago
she had blood work done, allergy tests, etc and there was nothing abnormal.... it turned out to be a habitual thing, she seems to chew on her backside near her rear and hind legs when she is angsty or bored i guess lol i ended up buying her a "cone" and it helps. It's an "every now and then" thing for her, she hadnt done it in a long time (since after my last post) but started up again when we started moving to our new place, after this i now believe that it is a nervous habit and/or anxiety related.