Dogs experience allergies to pollen, flea bites, and even food. With a food allergy, the immune system reacts adversely to one or several ingredients in the diet. Some dogs develop an abnormally intense reaction to certain ingredients, becoming hypersensitive.
Allergens usually come from meat protein sources (such as poultry, beef, pork, lamb, or fish) or from grain protein sources (such as corn, wheat, soybeans, or rice). Contrary to what many people think, a food allergy isn't a reaction to a new ingredient in the diet but a reaction to ingredients the dog's immune system recognizes, as with other types of allergies. In some cases, the intestinal lining in young dogs with intestinal parasites or infections is so damaged that the lining abnormally absorbs allergens.
Allergic reactions in dogs usually result in an uncontrollable itch on one part of the body—or all over. Food-allergic dogs tend to scratch intensely at their ears or lick at their anal area. On occasion, a food allergy appears as gastrointestinal distress, such as vomiting or diarrhea, or respiratory distress, including sneezing or breathing difficulty.
Risk factors and detection
There are no known risk factors for food allergy. However, food allergy is the third most common skin disease in dogs. Unlike other types of allergies, food allergies don't target a specific breed or gender.
If general allergy symptoms develop in a dog younger than 6 months or older than 6 years, the veterinarian likely will investigate a food allergy over other allergies, especially during the winter months when seasonal inhalant allergies are a less likely cause. Your veterinarian also may suspect a food allergy if the itching persists all year long or your dog doesn't respond well to treatments (such as steroids) for inhalant allergies.
Detecting a food allergy in your dog is relatively simple, but it requires time and discipline. Your veterinarian can use intradermal skin testing or blood tests to detect inhalant allergies in dogs. But the only way to detect a food allergy is through elimination diet trials using hypoallergenic foods.
Hypoallergenic foods must not contain any meat or grain proteins from your dog's usual diet. Many different hypoallergenic diets are available—your veterinarian can help you select the best one for your dog.
To conduct a valid allergy test, feed hypoallergenic food exclusively for four to eight weeks or more to eliminate all potentially allergic food products from your dog's system. During the test period, don't give your dog any vitamins, chewable toys, or medication that might contain an allergen. With discipline, the results can be dramatic. If your dog is hypersensitive to a food or an ingredient, he will show noticeable improvement by the fourth week of the trial. If your dog was treated with steroids, antihistamines, or fatty acid supplements, discontinue such treatments for 10 days to three weeks before the trial so they don't interfere with the trial by masking your dog's symptoms.
Most dog owners continue feeding the hypoallergenic diet once their pet's symptoms resolve. But if you want to identify what caused the allergic reaction in your dog, you can conduct a provocation diet trial. Work with your veterinarian to reintroduce meat and grain protein ingredients from the dog's original diet, one ingredient at a time, to see if the itching and scratching return. The trial for each ingredient may last up to 10 days, but in most dogs, clinical signs return within two days.
Prevention and treatment
Once you identify an allergen, eliminate that ingredient from your dog's diet or just continue feeding hypoallergenic foods. But keep in mind that a dog who is predisposed to food allergies may develop reactions to the new diet. If that occurs, you'll need to conduct a new elimination diet trial. In addition, a dog with allergies to one substance—whether it be fish, fleas, or grass—may have multiple allergies, which can complicate matters and require additional testing and treatment.
