Westie with allergy to chicken

My dog has an allergy to chicken, he's been eating Purina Little Bites his entire life but now they've added chicken to their food and he's extremely sick. I need to find him a new food without chicken but he's also had problems with beef in the past so I'm unsure as to what kind of food to use, any suggestions?

Buy lamb dog food. This is what's given to dogs with allergies.
   
Any good mid-level (Iams, Hills) is good; avoid Beneful, it has too many vegetables & most vets don't approve of it.
   
Read the side of the package to double-check the contents.