I have a shar pei bull mastiff mix that is losing his hair all up his back legs and most of his back. I thought it to be mange but when I went to my local farm supply place the lady said it sounds like an allergy to corn that is in the dog food, we have 5 dogs so we always just buy cheap food from wallmart, and to try the corn free food they sell. She said her dogs had the same problem and the food cured it. Our dogs have had mange in the past but not like this. Any ideas?