As to your exact question, I was told by a vet who specializes in dog allergies that some intestinal parasite infections can cause allergy type reactions in dogs. In fact, when I took my dog in, they gave me an anti-parasitic medication to give him for a few days without even testing for parasites (it’s easier/less expensive to give the treatment and see if the symptoms go away than it is to test). In my case, this didn’t work, but it might in yours.
On another note, my guess is that your dog likely isn’t allergic to all the things you mentioned (bones, antler, etc.) but is much more likely to be suffering from an environmental allergen (pollen, dust mites, grass, etc.). The only way to find this out is to take your dog to a vet that can test for a reaction to environmental allergens. It’s very much the same as how they test people for allergies – they have to shave off some of the hair, then they prick the skin in a bunch of small spots with various possible allergens. If your dog is allergic, there will be a skin reaction in the corresponding spot.
Basically, you’re going to go crazy if you keep trying to guess. I strongly recommend heading to the nearest vet that can do a skin test for allergic response – even if that means driving a long distance.
