Food allergy is a relatively uncommon problem in the dog and only accounts for approximately 3 to 15 percent of all allergies in dogs. Feline food allergy tends to be more common and has been reported to account for up to 40 percent of all allergy cases in cats.

Food allergies can develop in animals as a reaction to any ingredient in their food. Most often, this is due to an allergy to a protein component (ie. beef, chicken, fish, egg, etc.), or a carbohydrate (ie. corn, wheat, soy, etc.) in the diet, but may be due to an additive or preservative. The onset of the problem can develop at any age, and is not usually related to a diet change, as most animals have been eating the offending food for 2 or more years by the time they develop a problem.

Clinical signs

The most common sign is pruritus (itching).  Typically this is seen as:

• licking the feet
• chewing at the legs
• face rubbing
• licking the armpits, belly and groin  
• inflammation and redness of the skin
• head shaking and ear infections are also common
• scooting and perianal pruritus
• atypical signs can include vomiting and diarrhea 

Clinical signs associated with food allergy persist as long as the aggravating food item is present in the diet.

Diagnosis

There is no quick and simple test available to diagnose food allergy. Blood tests and intradermal skin tests are not useful in diagnosing food allergy. The only method to identify food allergy is to feed the pet a restricted diet for 8 to 12 weeks to determine if there is improvement in their clinical signs. If secondary infection is present (bacteria / yeast) it needs to be treated during the diet trial.

Since most commercial diets contain similar types of ingredients, simply changing the brand of food is unlikely to help. The goal is to feed a diet that contains a protein source that the pet has never eaten and it must be fed (exclusively) for 8 to 12 weeks. This is called a hypoallergenic diet, because an allergic reaction should not occur to a food that the animal has never before eaten. It often takes the full 8 to 12 weeks for the diet to work and alleviate the clinical signs. No other foods, treats, table scraps, rawhides, chewable medications (such as flavored heartworm medication), or anything flavored can be fed during the trial.

Diets should be introduced slowly over a 4 to 5 day period by gradually mixing the new food in with the former diet. This will minimize gastrointestinal upset (such as vomiting or loose stool). After the transition period and once the new diet is being fed as the only food source, this is to be considered Day 1 of the 8 to 12 week trial.

If there is only slight or no improvement seen after the 8 to 12 week trial, and it's confirmed that the pet has eaten nothing but this new diet, and all secondary infections have been concurrently treated, then it is most likely that there is another underlying cause of the skin problem, such as airborne pollens or an inhalant allergy.

* Keys to success of the Elimination Diet protocol

• Feed the pet only the prescribed diet. No other foods or treats are allowed.
  
  
• Make sure all family members and friends know that the pet is receiving a special diet, and not to give any other type of food.
  
  
• If you need to use treats for rewards or training purposes, use some of the prescribed diet.
  
  
• If there are other pets of the same species in the household, feed them the same diet or feed them separately.
  
  
• Keep the pet out of the room during your meals to avoid him or her picking up dropped food. 
  
  
• If pills are prescribed for the pet, don’t hide them in anything other than the prescribed diet. If giving medication to the pet is difficult, discuss this with your veterinarian.
  
  
• Flavored products, such as those found in medications, toothpaste, and certain plastic toys, must be avoided during the diet trial.
  
  
• If the pet is in the habit of eating dropped food or garbage when exercised outside, keep him or her on a leash. 
  
  

* Things to avoid in a diet trial

• Flavored vitamin supplements

• Flavored medications including chewable heartworm, flea, arthritis, etc., medication

• Rawhide chew toys, pig ears and other flavored chews

• Cat food (and cat litter boxes)

• Outdoor access (such as well-meaning neighbors with treats and small game such as rabbits, squirrel, birds, etc.)

• Substances used to conceal medications (cheese, lunch meat, peanut butter, etc.)

• Table food (difficult in households with small children)

• Toothpaste and other flavored dental products

• Access to an open dirty dishwasher

 
Suggestions for Success

Keep a food diary and record everything your pet eats during the food elimination trial and share it with your veterinarian. It is better to be honest in a food diary and acknowledge accidental lapses rather than fail to rule out a potential allergen.

Contributed by:  Karen Helton-Rhodes, DVM, Diplomate ACVD