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Veterinary Forum July 2008 (Vol 25, No 7)

Challenging Your Pet's Food Trial

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    Now that you have completed the first phase of the food trial, the elimination diet, it is time to challenge your pet with his or her original diet.  The goal of a food trial is to determine if your pet’s allergic skin disease is due to a component of the diet.  The first phase, which you have just completed, consisted of feeding your pet a strict hypoallergenic diet and watching for resolution of allergic signs, including itchiness, hair loss, redness, papules and crusts. Now that your pet’s skin disease has resolved, it is time to reintroduce the original diet to see if the skin disease returns.  Undoubtedly you are hesitant to cause a relapse in your pet’s allergic skin disease now that it has resolved. While the thought of a recurrence of signs is undesirable, there are several good reasons to go on to the next step of the food trial and challenge your pet with his or her original diet.

    The main reason to challenge your pet with the original diet is to obtain a definitive diagnosis of food allergy.  It is possible that your pet’s clinical signs have resolved reasons other than the food elimination trial; therefore, observing the return of those clinical signs when you begin to refeed your pet’s previous diet is the only way to determine that it is indeed the change to a hypoallergenic diet that has caused the improvement. In addition, it may be possible to identify specifically the items to which your pet is allergic. This will enable you to avoid the expense and possible inconvenience of feeding your pet the elimination diet for the rest of his or her life.

    The procedure for performing a food challenge is as follows:

    1. Introduce the original diet gradually over the course of 5 days, in such a way that meals progress from 75% hypoallergenic food and 25% original diet, to 50% and 50%, to 25% and 75%, to 100% the original diet.
    2. Monitor for reappearance of clinical signs (itching, redness, flaking).  If this occurs, discontinue the food challenge and consult your veterinary dermatologist.
    3. If no signs reappear after 2 weeks, slowly begin introducing your pet’s original treats, supplements and flavored medications.
    4. Monitor for reappearance of clinical signs (itching, redness, flaking).  If this occurs, discontinue the food challenge and consult your veterinary dermatologist.
    5. If no signs reappear 3 weeks after you being reintroducing treats, flavored medications, etc., consult your veterinary dermatologist about discontinuing all diet trials, as it is unlikely that your pet has a food allergy.   

    It is imperative that you avoid any breaks in the food trial because deviating from the above protocol may confound the challenge; there would be no way to know whether the break in the trial or the challenge truly caused recurrence of signs. If signs recur during the challenge period, a diagnosis of food allergies can be comfortably established and your pet can be placed back on his or her hypoallergenic diet.

    Once a diagnosis of food allergy has definitively been made, there are two ways to use this information. You may elect to maintain your pet on the hypoallergenic diet. Alternatively, you may choose to find precisely which ingredient(s) in the original food your pet is allergic to. This would be achieved by performing an individual ingredient elimination trial, in which one potentially allergenic ingredient at a time is introduced into your pet’s hypoallergenic diet.

    Click here to download this article as a PDF.

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