Not to do with your question, really, but my allergy doctor said that anyone at any time can develop allergies, it is your body having an immune system reaction inappropriately. In my case, I had other allergies, but no food allergies until ten years ago, when they developed out of the blue. That it happened to all your dogs at once of course suggests something in common, are they genetically connected? Or just all Rotties who live in your house and get the same treatment?