Hello!
By-product meal is the first or second ingredient in Royal Canin dog food. There are better options if it is in your son's budget to try an alternate food. When I first adopted my Frenchie, she was 1 year old, and had been on the "French Bulldog" formula by Royal Canin in her former home. The woman sent her home with us with a bag, but I took her off of it immediately. Her ears were red and itchy. I took her to the vet and they discovered she had a very bad ear infection that included pus! Mine is sensitive to chicken, so taking her off that brand was necessary. ACANA, Orijen, ZiwiPeak, Zignature, etc...are all higher quality foods. Many bulldogs are sensitive to chicken. You may want to try another protein. Mine does well on duck. I would say have your son take his dog to the vet for a quick check just to make sure it does not have an ear infection, which can be common for a dog experiencing allergies or sensitivities.