We took our dogs to the vet for their checkups the other day. The are a large breed, and require lots of exercise, so we spend a lot of time with them. The only problem we had noticed was that one of them appeared to have an ear problem, because she was constantly scratching at her ear, and rubbing it against surfaces, and occasionally she'd hurt herself and yelp. Long story short, the vet suggested a change in diet, something without any chicken in it. We read a handout about it and tried a change. After a week or so, no more annoying ear problems, other than normal amount of cleaning etc.
The information we found was from a handout by the Mountain Animal Hospital in Hamilton.