hi mate, ive had a similar problem with my bull bitch and in her case its an allergy to yeast, i hope this helps, good lucl
Your bang on Barney.The vet couldnt pinpoint what was causeing it so he told my mate to keep the dog away from nettles etc, treat the feet for mites,Reduce the protein.My mate tried all this and the dog was still chewing his feet.Too cut a long story short my mate took him back to the vets and it was found the dog had an intolerance to yeast.I think he just feeds the dog raw now and hes been fine so far.