Beagle Food Allergies

Question
I have a 5 and half year old Beagle.  The vet has told me that he has food allergies.  No matter what food I try symptoms seem to come back sometimes they are better than others though.  His symptoms include ear infections, scratching his bottom on the carpet and throwing up.  I use Mometamax fro his ears, which helps to clear them up.  The foods I have tried have been Nutro, Beneful, Putrina Pro Plan for Sensitive Stomach, Science Diet-Sensitive stomach and a few others that I can't rememeber.  I am currently trying a Purina on from the vet called LA it is supposed to have limited allergens.  I am so frustrated becasue I cannot find a food that works for him.  I think I am about to try the can food Canidae.  I was just wondering if you had any advice on what to try and why none of them work.  Thanks, Amanda

Answer
This is a case for looking at the ingredients.  If he is allergic to chicken, changing brands of chicken chow won't help.  If he is allergic to rice, Changing from chicken and rice to lamb and rice won't help.  I am not familiar with the Purina LA, but likely it substitutes less common ingredients for more common ones and may help the problem.  If it doesn't, keep working with your vet.