My border collie has been scratching under his chin so much that it bleeds. He's never had any health problems, but I have noticed lately that he is not interested in his food and wonder if maybe he has an allergy to it. I don't know if I should change is food or take him to the vet.

Thanks!
Jamie

If you are feeding a regular dog chow and little else, I would go to the vet. It could be parasites, a fungus, etc. Changing chows could complicate diagnoses and make things worse.

If you are adding very much else of this or that, cut it out. You could be ruining the carefully formulated complete and balanced diet and bringing on the itch.

It is common for herding dogs to refuse to over eat. You may be over feeding it. See the sticky, https://www.askmehelpdesk.com/dogs/information-articles-our-dogs-expert-labman-53153.html#post254171