Allergies are a common problem for dogs. Typical symptoms include itchiness resulting in excess scratching, biting, or licking, and sometimes chronic or recurrent skin/ear infections. While dogs most frequently suffer from allergies to environmental triggers (e.g., pollen, molds, and dust mites or flea bites), allergic reactions to food are possible, and are frequently a source of greater controversy.
Diagnosing canine food allergies is not easy. It typically requires a food trial during which a dog eats ABSOLUTELY NOTHING other than a food containing protein and carbohydrate sources to which he has never been exposed before. Another option is to only allow your dog to eat food that has been processed in such a way as to make it hypoallergenic. A food trial needs to continue for at least eight weeks before its success or failure can be evaluated. This is easier said than done!
I think the difficulty we have in definitively diagnosing food allergies in dogs is at least partially responsible for some of the myths that have developed around the condition. Let’s look at a few, along with the truths behind them.
Myth: Dogs are typically allergic to corn, wheat, soy, and other plant-based ingredients.
Truth: In a study of 278 cases of food allergies in dogs where the problem ingredient was clearly identified, beef was by far the biggest culprit (95 cases). Dairy was number two at 55 cases. Wheat came in third with 42 cases. Soy and corn were actually minimal offenders, coming in at 13 and 7 cases, respectively.
In fact, protein sources are more often to blame than grains. Beef, dairy, chicken, egg, lamb, soy, pork and fish were responsible for 231 of the food allergies, while wheat, corn and rice combined accounted for only 54. (Some dogs were allergic to more than one ingredient, which is why these numbers total more than 278.)
Myth: "I’ve changed my dog’s diet several times and he’s still itchy, so he can’t have a food allergy."
Truth: Dogs are allergic to particular ingredients, not to brands or types of food. So if your dog is allergic to chicken, and each of the foods you have tried contains chicken, he will still be itchy. Look very closely at the ingredient list; it will usually contain multiple protein and carbohydrate sources. It is not unusual for a food that is labeled "lamb and rice," for example, to contain chicken or other potential allergens as well.
It is difficult to guess correctly as to what your dog might be allergic to, which is why veterinarians typically reach for foods with novel ingredients like venison and potato (your dog’s dietary history is important for picking out the right one), or specially processed, hypoallergenic foods.
Myth: "I haven’t changed my dog’s diet. It’s hard to believe that he would be developing a food allergy now."
Truth: Dogs can develop food allergies at any time in their life, and with any dietary history.
Myth: "If my dog is suffering from food allergies, why doesn’t he have diarrhea?"
Truth: Some, but not all, dogs with food allergies have concurrent gastrointestinal signs like vomiting or diarrhea, so you shouldn’t rule out food allergies just because his GI tract seems to be functioning normally. If your dog has chronic gastrointestinal problems in addition to non-seasonal itchiness, a food allergy will be at the top of the list of potential problems.
If you think that your dog could have a food allergy, talk to your veterinarian. He or she can help you find the right food to keep your dog’s symptoms at bay while still providing the balanced nutrition that is essential to good health.
Dr. Jennifer Coates