Dogs and cats can become allergic to components of their diet whether they have been eating the same food for years or they have recently been introduced to a new brand or type. Food allergies or hypersensitivities are relatively uncommon but should be suspected if an animal develops itchy skin, vomiting and/or diarrhea and other more frequently diagnosed disorders (e.g., allergies to environmental triggers like pollens or molds, fleas or primary gastrointestinal disease) have been ruled out.
To diagnose a food allergy, a pet must be fed a diet that contains protein and carbohydrate sources that the animal has never eaten before. Commercially prepared foods that are made with venison, duck, rabbit and potato are available, or an owner may choose to prepare a homemade version. All diets must be nutritionally complete and should avoid beef, lamb, pork, soybean, egg, dairy, corn, wheat, barley, rice and for cats, fish as most animals have been exposed to foods containing these ingredients. Any treats that are fed should contain the same ingredients as the pet's new food. All other potential sources of dietary allergens, including table scraps and chewable medications, must be eliminated. Owners need to feed this strictly limited diet for two to three months and monitor their pets for any improvements in their clinical signs before the dietary trial can be deemed a success or failure.
If a pet's condition improves significantly during the diagnostic period, food allergies are at least partially to blame for its symptoms. Owners may elect to continue feeding the same diet that was used during the food trial or to reintroduce protein and carbohydrate sources one at a time to determine what the trigger may be. An animal's symptoms should return within one to ten days of being fed an offending ingredient. Whichever approach is taken, lifelong avoidance of the substances that trigger an allergic reaction is necessary to keep food-allergic pets healthy and happy.