What is it?
Cats and dogs can develop an allergy to an ingredient in their diet. Usually the allergy will be directed against a protein (chicken, beef, egg, and dairy are the most common). While “grain-free” diets are a popular fad right now, it’s very rare for pets to be allergic to grains such as wheat, corn, or gluten.
What are the signs of food allergy?
Most pets with a food allergy will be extremely itchy all year round. Many don’t improve with traditional anti-itch medications like antihistamines, steroids, or Apoquel. Usually signs will develop before 1 year of age or later in life like 8-9 years. Any breed can get food allergy, but some breeds are predisposed such as the German Shepherd dog and Cocker Spaniels. About 20% of pets will also have GI signs like vomiting, diarrhea, or frequent bowel movements (pooping 3-4 times daily). A smaller subset of food allergic pets won’t be itchy at all, but instead will get recurrent skin and ear infections that are very hard to resolve.
How is food allergy diagnosed?
Food allergy can be very challenging because there is no valid test to diagnose it. You can read about blood, saliva, and hair tests online, but if you find the fine print, they all mention that their tests are not valid diagnostic tools, so we never recommend performing these tests for food allergy. The only valid way to diagnose food allergy is through a strict prescription hypoallergenic diet trial. A special food is selected that is not expected to cause food allergy and that is feed exclusively for 8-12 weeks. You can use either a novel protein, meaning a protein source the dog has never been exposed to before (rabbit, venison, kangaroo, etc); or you can use a hydrolyzed diet (Royal Canin HP, Ultamino, Hill’s Z/D), meaning the protein has been broken up into such small particles that the immune system cannot recognize it as an allergy (though they still get calories from the food). If the skin condition improves by the end of the diet trial, that suggests the pet has a food allergy. To prove it for sure, we rechallenge the diet by giving either the previous pet food or a certain ingredient (such as chicken breast). If the patient is allergic to that new ingredient, they will get itchy within 24-48 hours (watch closely for up to 1 week just to be sure). If the patient does not improve at all at the end of the strict diet trial, that suggests that food allergy is not the cause of their skin problems and other causes will be investigated (such as environmental allergies).
What does a “strict” diet trial mean?
The pet has to eat only the special prescription food for 8-12 weeks with no treats, rawhides, table scraps, toothpaste, flavored medications, oral heartworm medications, or pill pockets. We switch to a topical heartworm preventative such as Advantage multi or Revolution. If the client needs something to hide pills, we use the canned food version of the special diet to make little meatballs. If the client needs to give treats for training or emotional reasons, they can use a few kibbles of the special food, or they can bake the canned food into little cookies (we have a separate handout with baking instructions). If a mistake happens and the pet eats something other than the special prescription diet, the diet trial needs to be started over, which will cost the owner more money in the long-run, so it’s best to be as strict as possible from the beginning.
Can I use an over-the-counter diet with special ingredients?
Not for the diet trial. Over-the-counter diets like Blue Buffalo may claim to have special ingredients like venison, but they are made in the same factory as regular pet food. Studies have shown that many of these over-the-counter diets still contain normal pet-food proteins like beef, which means they are not appropriate for a strict diet trial. Prescription hypoallergenic diets are made in separate factories or have special cleaning procedures between different foods, so they are guaranteed to be pure. That is why we have to spend the extra money on prescription food for the diet trial. Remember that this is only for 8-12 weeks, and we’re using the special food as a test to prove whether or not the pet has food allergies. After the test is over, we may be able to change to an over-the-counter diet for long-term use.
What is the prognosis for a pet with food allergy?
Pets with food allergy are expected to have a normal life-span. Their allergies can be well-controlled for life if the owners are careful with their diet. In a way, having a diagnosis of food allergy is better than other allergies because it can be managed with diet change alone, and doesn’t require medications for life that can have side effects.
