When I brushed him on monday I noticed that about a 3 inch section of his mane about half the way down started to come away. Over the past couple of days it has come away even more and that area of mane is almost completly bald. It is not affecting any other part of his mane, coat or tail, just this 3 inch section. I have ruled out mites and a fungal infection. But am now at a complete loss as to what it can be. Help!