Food Allergies in Dogs and Cats

By Amy J. Randall, DVM, MS, Diplomate, ACVD

    Food allergy (hypersensitivity or food intolerance) is a common skin disorder in dogs and cats that is caused by an allergic reaction to food. The component of the food that the animal reacts to is the protein. Most common proteins include beef, chicken, fish, egg, dairy, soy, corn, wheat and rice. However, there is also concern with other components of diets including preservatives, additives and dyes. Because this is an acquired disease, the animal often has been fed the food for months and even years prior to the onset of the allergy.

     The most common signs of food allergy are non-seasonal itching, licking and chewing. In dogs, the itch tends to be generalized, but the ears, face, feet and rear may be more severely affected. Some dogs may exhibit signs of recurrent ear and skin infections as the only manifestation of food allergy. Food allergy in cats usually affects the face and neck, and the itch may be so severe that the animal scratches itself until it bleeds or there is significant hair loss. Up to 35% of animals with food allergies have accompanying gastrointestinal signs (vomiting, diarrhea, soft or mucousy bowel movements). In both species, the disease may be poorly responsive to steroids (prednisone). The majority of dogs and cats with food allergies manifest clinical signs at a very young (less than one year of age) and extremely old age. However, the problem may occur at any age.

     The diagnosis of food allergy involves a food elimination trial. There is currently no other accurate test to determine if your pet has a food allergy. The blood testing for food allergies offered by several independent laboratories across the country provide too many false positive and false negative results. It is believed that animals may react to allergens in their food for up to six weeks or more; therefore a restrictive diet must be given for up to 6 - 8 weeks. Because food allergy is an acquired disease (a food component becomes allergenic after being fed), only foods that the animal has never eaten before may be used. One protein source and one carbohydrate source are chosen, and all other foods are discontinued. It is important to be complete when relating your animal’s diet history so that an appropriate diet may be chosen for your pet.

     Most common limited ingredient diets available for food trials include venison and potato or sweet potato, duck and potato or sweet potato, kangaroo and oat, fish and potato or sweet potato, rabbit and potato. Many of these diets are prescription diets which can be purchased through your primary veterinarian or dermatologist.

     During a food trial, the prescribed diet is fed exclusively for the period of time recommended by a veterinary dermatologist or your primary veterinarian. Treats, rawhide chews, dog biscuits, pig’s ears, chew hooves, chewable vitamins, food supplements, or unapproved medications (including chewable heartworm and chewable flea preventions) may not be given. Your dermatologist or primary veterinarian may change your pet’s heartworm preventative to a non-flavored liquid for the duration of the trial period. Components of the trial diet may be used to administer medications. You may not use cheese, hot dogs, bread, peanut butter, etc., to disguise medication during the diet trial. Treats must consist of the same ingredients used in the diet trial. Example: Serenegy offers potato, duck and potato and oats treats which are all natural and human grade ingredients.

     Outdoor cats must be kept away from other food sources to have a successful food trial. It may be necessary to confine them indoors for the duration of the trial. Please exercise caution if you have other pets and make certain that the pet on the trial diet never gets an opportunity to eat any of the other animal’s food (or even lick their bowl!). One morsel of another type of food has the potential to invalidate the entire elimination diet trial and could necessitate commencement of a different diet for 6 – 8 weeks.

     If necessary, other animals in the household could also be fed the elimination diet. Inform everyone in the household, the bank teller or gas station attendant, etc. that your pet is on a special diet. It is important to be diligent when your pet is on walks to ensure that ingestion of foodstuffs does not occur. Simply changing the brand of dog food (even to diets described as “hypoallergenic”) is not equivalent to an elimination diet. Most dog foods share similar protein, grain meal, preservatives, and/or dye sources.

     Your primary veterinarian or dermatologist will recommend a restricted or hydrolyzed protein diet. Switch gradually to the new diet over a period of four days by giving each diet 50/50. At the end of the 4-day transition period, feed only the new diet. Some animals may have loose stools while receiving the trial diet. Your pet may develop vomiting, diarrhea, constipation or may refuse to eat the new diet. Cats may begin to develop a serious liver disease if they do not eat for two days or more. Do not allow your cat to go without eating for more than two – three days. Consult with your primary veterinarian or dermatologist if any of the other problems occur before giving up or changing the diet. It is advisable to keep a daily diary during the trial so that progress may be monitored.

SUMMARY:

1. Various foods, food preservatives and additives, when ingested may
cause itchy skin disease and/or intestinal disease in certain animals.

2. This is an acquired disease and frequently the animal may have been
ingesting the allergic food for months to years before any problems arise.

3. There is currently no accurate blood or skin test to tell if your pet has a
food allergy. The only method is by avoidance and challenge.

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