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Food Allergies and the Itchy Dog

Itchy skin in the small animal is often more than just a minor annoyance. Red, oozing bald patches; rashes; and large expanses of hair loss are unfortunate markers of very real discomfort for which a cause should be sought and dealt with.  Flea control is always fundamental when it comes to itch control but of course there can be other causes.  Thankfully due to the newer and safer technology of products like Bravecto, the oral flea & tick preventative also works against mites (microscopic litter critters that are everywhere like dust mites in your bed).

The food allergy is one of the itchiest conditions known to cats and dogs. Animals eat a variety of processed food proteins, fillers, and colorings that are further processed inside their bodies. Proteins may be combined or changed into substances recognized by the immune system as foreign invaders to be attacked. The resulting inflammation may target the gastrointestinal (GI) tract or other organ systems, but in dogs and cats it is the skin that most often suffers from this immunologic activity.

Many people erroneously assume itching due to food allergy requires a recent diet change of some sort. In fact, the opposite is true.

Food allergy requires time to develop; most animals have been eating the offending food for years with no trouble.

What Kind of Allergy?

Sarcoptic mange and inhalant allergy (also known as atopy) are the two conditions which must be distinguished from food allergy as the treatment approach to each is markedly different. Much time and money can be wasted pursuing the wrong problem.

Please consider the following clues that contribute to pointing us towards the food allergy as a diagnosis. Your pet demonstrates:

  • Your pet has been treated for sarcoptic mange without any positive change.
  • Your pet’s itchiness is not and has never been a seasonal problem.
  • Your pet has responded poorly or only partially to cortisone-type medications.
  • Your pet has had a skin biopsy demonstrating changes often associated with allergy or, more specifically, food allergy.
  • A lesion distribution pattern that is common for food allergy (see illustration above).
  • Your pet did not have skin issues before age 5 or 6.

Any of the above findings or observations warrant pursuit of food allergy.

How to Deal with the Food Allergy Suspect: The Hypoallergenic Diet Trial

The Basic Principle
To determine whether or not a food allergy or intolerance is causing the skin problem, a hypoallergenic diet is fed for a set period of time. If the pet recovers, the original diet is fed for up to two weeks to see if itching resumes. If we see recovery with the test diet and itch with the original diet, then food allergy is diagnosed and the pet is returned to either the test diet or another appropriate commercial food indefinitely.

What is a Good Hypoallergenic Diet?

Fortunately, many pet food companies have discerned the need for diets using unusual protein and carbohydrate sources with a minimum of additives. Foods can be obtained based on venison and potato, fish and potato, egg and rice, duck and pea, and even kangaroo. Diets used for allergy trials must contain basically one protein and one carbohydrate source and neither can be something the pet has had before. Recently several diets that include duck, venison, kangaroo and rabbit have been released to the general market. Be aware of foods that contain these ingredients because these ingredients will not be usable for future diet trials if they were ever used in the pet’s regular food.

It is important that no unnecessary medications be given during the diet trial. No edible chew toys (such as rawhides or bones) should be given. Treats must be based on the same food sources as the test diet. (Beware of rice cakes, though, as wheat is commonly used as a filler.) Chewable heartworm preventives should be replaced with tablets.

The Hydrolyzed Protein Method

Recently a new approach has been introduced using therapeutic diets made from hydrolyzed proteins. This means that a conventional protein source is used but the protein is broken down into molecules too small to excite the immune system. Some hydrolyzed diets are on the market; discuss with your veterinarian which is best for your pet.

How Long to Feed the Trial Diet

In the past, four weeks was thought to represent a complete trial period. More recent work has shown that only one food allergic dog in four will respond within this time frame and that a more appropriate trial period would be 10 to 12 weeks.  Eighty percent of food-allergic dogs will have responded to diet trial at least partially by six weeks. The Labrador retriever and cocker spaniel appear to require longer trials.

Most commercial diets used in food allergy trials have a 100% guarantee. This means that if your pet doesn’t like the food, the food can be returned for a complete refund, even if the bag is opened. This is especially helpful for feline patients, as cats are famous for being choosy about what they are willing to eat.

What to do if the Diet isn’t Successful?

If diet alone is not controlling the itch then the problem lies in environmental allergies or a combination of allergies may be at hand.  Thankfully there is a broad spectrum of treatment for the itchy dogs these days and with certainly less side effects than the historical standard of steroid usage.

Cameron S. Dow, DVM
Prescott Animal Hospital