Friday, October 28, 2011

Allergies in Dogs and Cats - Part one - Food

Your Pet’s Itchy Skin

Itchy skin on your pet can be due to parasites, (fleas and sarcoptic mange) food allergy, and inhalant allergy (atopy).  Itchy and inflamed skin oozes and gets traumatized by the pet causing secondary infections.  Sometimes the secondary infection causes added itching! Ears are a continuation of your pet’s skin-if they have recurring ear infections (otitis), think allergies!  (Most people think itchy ears are mites, but out of all the dogs we see every day as veterinarians, probably one in one hundred has mites.  Cats and kittens are more commonly having mites in the ears, but this is easily treated and cats are much less commonly suffering from allergy related ear infections).

What Kind of Allergy?
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 activity. 

The top four allergenic foods in dogs are beef, dairy, wheat and chicken.  In cats, it’s beef, dairy, and fish.  But don’t assume that if you eliminate one or all of these proteins that your pet doesn’t have a food allergy.  Discuss how to do a proper diet trial with your veterinarian.

Many people erroneously assume itching due to food allergy requires a recent diet change of some sort.  But food allergy requires time to develop; most animals have been eating the offending food for a long time (months to years) with no trouble. 

To determine whether or not a food allergy or intolerance is causing the skin problem, a hypoallergenic or novel protein diet(a protein that the pet has never eaten before such as kangaroo, venison, duck, or hydrolyzed soy protein, etc. ) is fed for a set period of time, usually recommended to be 12 weeks.   

During this initial period, the skin infections need to be cleared up as best as possible to assess the pet’s level of itching and inflammation.  If the pet is not itching on the novel protein diet, food challenges can be fed for up to two weeks to see if itching resumes. (For example, we add chicken to the diet for two weeks to see if the pet itches or becomes red or smelly, then we try beef for two weeks, etc.)  

If the pet begins to itch within 2 weeks, then that protein source represents one of the pet's allergens. Return to the test diet until the itching stops and try another pure protein source. If no itching results after two weeks of feeding a test protein, the pet is not allergic to this protein.  

If we see recovery with the test diet and itch with another protein, then food allergy is diagnosed and the pet is returned to either the test diet or another appropriate commercial food without the offending protein(s) indefinitely. 

Photo Credit: Garry Cook
Many people do not want to take a chance of returning to itching if the patient is doing well; it is not unreasonable to simply stay with the test diet if the pet remains free of symptoms. It is important that no unnecessary medications be given during the diet trial. No rawhides or bones, dog biscuits, rice cakes or puffs, table food, etc. should be given

Treats must be based on the same food sources as the test diet-I actually recommend feeding the dry kibble as a treat, a bit of the canned food, or you can bake the canned food version into a “cookie”. Check and see if your pet’s chewable heartworm preventives are flavored with real proteins. If so, they should be replaced with tablets.

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.

Sarcoptic mange and inhalant allergy (also known as atopy) are the two conditions which must be ruled out from food allergy.  Lots of time and money can be wasted as the treatment for each is totally different. 

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 (steroids, prednisone) medications.
  • Your pet has had a skin biopsy demonstrating changes often associated with allergy or, more specifically, food allergy. 
Stay tuned for our next blog on Flea Allergies!

By: Dr. Dana Lewis
Dr. Dana assists families in the Raleigh North Carolina area (Raleigh, Durham, Chapel Hill and the greater Triangle, as well as Wake, Durham, Orange, and Chatham counties.)

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