“Food allergies in dogs present themselves quite differently than food allergies in humans,” Patterson said. “For instance a person who is allergic to shellfish may experience throat swelling and a possibly critical or fatal reaction, but in dogs the allergy is expressed through the skin and seen most often as itch.”
Dogs who itch, lick, chew, rub, bite, and scratch themselves year round, typically around the face, ears, armpits, groin, paws, and around the anus may be showing signs of a food allergy. Since itchy flare factors have an additive effect, it is important to eliminate other possible causes of itching. First, it is necessary to eliminate any possibility that parasites, particularly fleas, are causing the dog to itch. Likewise, the veterinarian should also look for signs of skin infections (bacteria and/or yeast). Secondly, the veterinarian will also determine if environmental factors are causing itchy skin. Dogs with year-round itch, who eat roughly the same diet yearlong, are frequently candidates for a food allergy diagnosis.
“There isn’t a conclusive clinical skin or blood [serum] test to see whether a dog has a food allergy,” Patterson said. “It’s like flipping a coin to determine whether the test is a true or false positive. Because of this, we have to base our diagnosis on the dog’s history, clinical signs of skin disease, and response to a food trial. The test for food allergies in dogs simply isn’t conclusive at this time, but we hope some of our research will lead to an effective test.”
To diagnose a dog with food allergy, the first thing to do is put the patient on an elimination diet, or an “exclusive novel protein diet. This ends up being a diet with individual ingredients to which the dog has rarely ever consumed before. Usually, the diet is commercially prepared and fed for a minimum of eight weeks.
The goal is to determine if food is a component of the itching.
Typically dogs are allergic to proteins they are exposed to for extended periods of time. In the United States, dogs are generally allergic to beef, chicken, and egg protein. Patterson explained that most elimination diets replace beef, chicken, and egg based foods with an exotic meat protein like venison, duck, kangaroo, or vegetable-based. After eight weeks, the patient is “challenged” by returning to the original diet. If the dog’s symptoms (itch) improved during the eight weeks, then return when the dog’s original diet is replaced, then a food allergy is confirmed.
“Patients with food allergies typically relapse within two weeks of returning to the original diet,” Patterson said. “It is important during the elimination diet to remove any flavored medicines or supplements, table scraps, typical treats, rawhides, and pill pockets from the animal’s diet so the test isn’t compromised.”
If a commercially prepared novel protein diet is not sufficient, a prescription hydrolyzed diet may be necessary. This food is only available by prescription from a veterinarian. It helps dogs with food allergies by breaking down the protein into small enough fragments that the immune system cannot recognize it, and, therefore, does not induce a skin reaction.
Another option for dogs with food allergies is a limited ingredient home-cooked diet. Patterson recommends only doing this under close supervision of a veterinarian.
While any breed is susceptible to food allergies, Patterson sees many poodles, boxers, weimaraner, dachshunds, chocolate labs, and German shepherds with food allergies. He has also noticed dogs with German lineages tend to be more susceptible to food allergies.
Generally dogs diagnosed with food allergies can remain on commercially prepared elimination diets for life without complications.
“As with any skin disease, there really isn’t a cure,” Patterson said. “Instead, proper management of the disease can keep dogs happy and healthy lifelong.”