My 10 year old Sheltie (male/neutered), started losing hair around age 6. It started with his tail and has been slowly working it's way up to his ruff. He has lost all his undercoat. He looks awful. I've been to 3 different primary care vets, a canine dermatologist, canine oncologist and canine nutritionist. My dog has had every test under the sun, some several times by different vets. No one can find an answer. If anyone can help, I'd appreciate it.