Allergic conditions are very commonly seen in pets. Many of the allergic conditions seen are due to seasonal allergies and a wide variety of other causes. However, 5-15% of dogs and 1-10% of cats with skin or ear disorders are likely to be food allergic. There are no recognized age, sex, or breed predilections. The age of onset is 4 months to 14 years in dogs and 3 months to 11 years in cats.
The most common sign of food allergy in both dogs and cats is itching, scratching, biting, or licking the skin. In dogs the itching is often generalized but in many cases is limited to the face, ears, legs, feet, armpit and groin area, and/or the area around the anus. In cats, the head, neck, ears, around the eyes and in front of the ears are commonly affected, but other areas may be involved. Ear infection is often present and may be the only clinical sign in dogs and cats. Skin redness, hyperpigmentation (darkening of the skin), infection, ulcerations, hair loss, scaling, and flaking are other clinical signs. Approximately 30-50% of animals with skin signs of food allergy also have signs of vomiting, diarrhea, increased frequency of defecation, and abdominal pain.
Other possibilities for the clinical signs described above include fleas, mites, lice, bacterial and yeast infection, contact allergy, and atopy (hypersensitivity to substances in the environment including house dust mites). Many animals have combined allergies (both atopy and food allergy). Non-seasonal allergies (late fall and winter months) can be highly indicative of food allergy.
Foods reported to cause allergies in dogs include beef, chicken, corn, dairy, egg, soy, and wheat. Uncommon food include fish, lamb, pork, rabbit, duck, and venison. In cats, common foods include beef, fish, and dairy. Uncommon foods include wheat, barley, egg, lamb, pork, poultry, rabbit, and duck.
The main challenge of performing a food trial is compliance. A food trial will fail if you feed treats, snacks, rawhides, pig ears, human foods, scraps, garbage, outdoor feeding, and any other items not specifically ordered in the food trial. There are three food trial options available: 1) veterinary therapeutic/prescription food, 2) over the counter (OTC) food, or 3) formulated home-prepared recipe. There are advantages and disadvantages to each approach.
Veterinary diets include novel protein and hydrolyzed therapeutic diets. Novel protein diets include ingredients such as rabbit, venison, fish, duck, or kangaroo, on the theory that other commercial pet foods rarely use these ingredients, so previous exposure is not likely. More and more OTC retail products are becoming available with these ingredients but some are contaminated with possible food allergy offending ingredients. Also, most novel protein veterinary diets are formulated for adult maintenance, not growth or reproduction. Hydrolyzed diets are not designed to be novel. They are formulated to provide small peptides, that are not recognized by the immune system, instead of larger intact proteins. These diets may be chosen if an animal has been exposed to several different diets in the past. Over the counter foods may be offered but limited data suggests that cross-contamination of retail foods can lead to traces of other ingredients. Lastly, home-prepared diets may be offered but they can be expensive, inconvenient, time-consuming to prepare, and difficult to formulate as complete and balanced (vitamins, minerals, etc.).
Animals with immunologic food allergies and food responsive gastrointestinal symptoms usually respond positively to food trials within 4 to 12 weeks. Clinical signs, such as itching, ear infections, and gastrointestinal upset will start to improve in the first month, but up to three months may be necessary to see significant improvement. Secondary bacterial and yeast infections will need to be treated during the early stages of a food trial. Be sure to use a topical flea and tick preventative during the appropriate months, as ectoparasites can cause many of the same skin and ear symptoms seen with food and environmental allergies.