I was told my dog might have food allergies, but he has eaten the same food his whole life. How can he now have a food allergy?
Unlike people, who may have an allergy to a food they rarely eat such as peanuts or strawberries, pets typically develop allergies to foods that they have been exposed to for prolonged periods.
In an allergic reaction to food, antibodies develop to a particular component of the food, usually a protein or complex carbohydrate. It takes time for the body to develop these antibodies. Therefore, it is most common for a food allergy to develop after eating the same brand, type or form of food for months or even years with no trouble.
Although a food allergy can cause GI disturbances in pets, most often the allergy manifests as skin or ear problems. Food allergies are one of the itchiest conditions that pets can get. In dogs, signs classically include chewing on the feet or limbs, facial or belly itching and ear infections. Cats most often have itchiness or scabs around the face and neck areas.
Almost any food ingredient can cause an allergic response. However, there are some more common offenders. The top three reported food allergens in dogs are beef, dairy products and wheat, accounting for 68% of canine food allergies. In cats, accounting for 80%, the top three food allergens are beef, dairy products and fish.
There is no gender predisposition to food allergies. In dogs the reported age range is 4 months to 14 years. However, up to one-third of cases may occur in dogs under one year of age. The age range of affected felines is also broad, varying from six months to twelve years. According to one study of cats with food allergies, nearly half the cats affected had developed signs of the disease by two years of age.
A pet with a food allergy often also has other types of allergies, such as flea allergies or environmental allergies (atopy). In fact, up to 50% of dogs and 30% of cats with suspected food allergies have concurrent flea allergies or atopy. So strict flea control is essential for any itchy pet to ensure fleas are not a complicating factor.
A food allergy can only be diagnosed by doing a test known as a food trial. During a food trial, your pet is exclusively fed a special hypoallergenic diet for 8-12 weeks. This diet contains limited ingredients including as a novel protein and a novel carbohydrate source (ingredients your pet has never been exposed to before, such as duck, venison, green pea, or rabbit).
A food trial has a very strict, but simple, protocol. Your pet can have water and the special prescribed diet and nothing else. Treats, chew toys, anything flavored such as certain types of preventatives, table scraps, etc. are completely off limits. Giving you pet any of these things invalidates the feeding trial; so the entire family, friends and other visitors must understand and follow the rules for the trial to be successful.
If you pet’s itchiness and/or GI signs improve or resolve during the feeding trial, then the test is positive for food allergies. To determine the specific food allergen, you can slowly reintroduce one ingredient at a time and see if that causes the itchiness starts again.
Most commonly, however, I follow the “if it ain’t broke, don’t fix it” rule, and continue with the hypoallergenic that resulted in improvement of the signs. Sometimes it might take several food trials with different limited ingredients to find what is best for your pet, so patience and not getting discouraged are keys to success.