If your dog or cat is itchy and we have ruled out parasitic and infectious causes (see our Itchy Pet handout which discusses parasites and infection in more detail), he or she may have a food allergy.
A food allergy occurs when the immune system starts reacting to a specific component in your pet’s diet. This reaction can occur within weeks of being fed the “allergic” food or may take years to develop. Therefore, a food allergy can start as a puppy/kitten, an adult, or as a senior pet. Food allergies can cause itching anywhere on the body and many pets with food allergies have chronic ear infections. Some food allergic pets also have histories of recurrent vomiting or diarrhea.
What food is causing the allergy? Since proteins are a much larger molecule than carbohydrates and are therefore easier for the immune system to “see” and react to, most pets are allergic to the protein in their diet. Allergies to carbohydrates are less common, therefore feeding a “grain-free” diet does not typically help a food allergic dog. The immune system can only develop an allergy to a food it’s been exposed to, therefore, it’s important to determine what foods the pet has eaten. Chicken is the most common food to cause an allergy because there are so many pet foods and treats containing chicken. We must emphasize that chicken is not more allergenic than other foods, it just is the most prevalent protein in our pet foods. An animal can develop an allergy to any food that it’s eaten, and if your pet has been eating fish, lamb, venison, etc., then your pet may have an allergy to those foods.
So what pet food should you switch to? First, it is extremely important that the correct food is chosen during this trial phase since the diagnosis can only be accurately made when the itching improves after an elimination diet is fed. Secondly, during the food trial, nothing else can be fed, including meat-flavored medications which include many oral preventatives. It typically takes 4 to 8 weeks for the immune system to quiet down and the pet to stop itching on the new diet- typically either a hydrolyzed or novel protein food.
A hydrolyzed food is one where the protein and carbohydrate components are broken down so that when the food is digested and absorbed, it enters the blood stream as such a small molecule that the immune system can’t react to it. Since a pet can develop an allergy in just weeks of being fed a new food, some dermatologists prefer using a hydrolyzed diet to diagnose a food allergy since the pet can’t develop an allergy to these diets during the 2 month trial phase. We recommend Royal Canin HP, Royal Canin XP, Hills Z/D, Purina HA hydrolyzed diets.
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Another option is to feed a “novel’ food diet. This involves feeding a pet food that has ingredients the pet has never been fed before. It is very important to be careful in selecting these foods. Many pet foods have other proteins beyond what is listed on the label due to cross contamination from other foods processed in the same equipment. If a dog is still eating very small amounts of the protein that they’re allergic to, then the itching won’t improve and the food allergy diagnosis will be missed. It’s similar to people with peanut allergies- some people can tolerate some peanut exposure and others can’t even be in a room with peanuts. This is why it’s very important to consult with your veterinarian when selecting which food will best diagnose your pet’s possible food allergy. We recommend Royal Canin, Hills, and Purina’s limited ingredient diets as well as certain over-the-counter foods. Foods can also be purchased through RayneNutrition.com– they even have alligator treats!
Another option is to cook for your pet. This way you have total control over what ingredients your pet is ingesting. You can use venison (if not previously exposed to beef or lamb), duck (if not previously exposed to chicken), pork, ostrich, emu, pheasant, rabbit, goat, elk, moose, alligator, kangaroo. These meats can be purchased from Avon Prime Meats in Avon, Ct or may be ordered from www.MyPetGrocer.com. If you would like to have a diet custom made for your pet, we recommend www.balanceit.com. This company also sell supplements to be sure your pet is getting sufficient vitamins and calcium in their diet.
What If My Pet’s Allergies Don’t Improve?
What if there is no improvement after the 8 week food trial? We may recommend trying a different diet- either switching from hydrolyzed to novel protein (or vice versa), trying a different protein diet, or home-cooking to control exactly what your pet eats. If your pet does not respond to the food trial, then an environmental allergy (atopy) is diagnosed- see our handout on Atopy for more information.