Food Allergies

We got our White Lab puppy, " Bailey" when she was 7 weeks old. We stopped at Petsmart on our way home with her and bought the same puppy food the Breeder had been feeding her, a pillow, a puppy collar and some toys. All the new puppy essentials. We got home, played with her, fed her and then settled her on her new bed in the laundry room for the night. When she started whining, I took her out to potty and then into my bed until she dozed off again , then I put her back into her own bed in the laundry room. She slept through the night and I took her out early the next morning for her potties again. She did pretty good, no accidents in the house. She plays and sleeps and eats, and seems to be settling into her new home just fine. So far so good, but why is she scratching so much? We examine her for fleas and find none. We start suspecting a possible food allergy and that starts our investigation into food allergies. It takes a lot of trial and error to diagnose potential food allergies and it would be a while before we found almost everything Bailey was allergic too.