This isn't really an urgent problem but one that I am monitoring and am curious to know what is causing it.

My male Briard who is nearly 1 yr old has white patches of fur on both of his knees. He is fawn. Over the last few months he has been nibbling where the white patches of fur are. He doesn't nibble anywhere else on his body, just these two areas. He also has a big white streak down the front of his chest, this doesn't appear to irritate or bother him. In all aspects, he is behaving normally. He is not excessively nibbling but he does do it at least once or twice a day for a few minutes each time.

He is having his first proper undercoat moult at the moment but his coat wont be fully in for another 6 months or so.

I have looked at the skin underneath the fur and it is normal in colour with no redness, bumps, lumps etc. He doesn't have fleas, ticks or any other nasty. I am fully grooming him at least 3 times a week and there are no problems elsewhere. Have never had a Briard with white knees before or this particular problem.

Any ideas?

Could it be growing pains?  Does he do it after hard exercise? 

Not really, there is no fixed times when he does do it. I find it really strange that he just nibbles these areas, perhaps the skin is different there, pigment or something that is making the fur white. Sounds crazy I know :-D

I have a rescue WSD who does this to both front knees - he spent the first year of his life on a chain and is a failed cattle dog. I think he probably started this habit through boredom or stress. When I first had him both knees were pink (he has white knees) and the hair was chewed really short. He rarely does this now but if he does I just redirect his attention to something else which seems to work.

If he has done a lot of chewing the skin underneath feels "gritty" and the hair looks as though I have cut it really short with a pair of blunt scissors.