Food hypersensitivity in the dog and cat: now what do I feed? (Proceedings)
Food hypersensitivity, food intolerance and other adverse reactions to food (ARF) could be the subject of a carrier of study. Food hypersensitivity in the dog and cat can cause a myriad of effects on several different systems of the body, with the integument and digestive system being most commonly affected. These notes will hopefully give insight into how ARF will affect the skin in dogs and cats.Because food hypersensitivy can be the manifestation of a type I, III or IV hypersensitivity reaction, the onset of clinical signs can range from minutes to days after ingestion of the offending allergen. In humans the allergen usually has a molecular weight above 12,000 Daltons, although this has not been confirmed in domestic animals, where the offending allergen may be smaller. A number of studies published over the years have listed the most common food allergens in dogs and cats. Summarizing these reports has led many dermatologists to conclude that animals have the potential or ability to become allergic to any food stuff to which they are exposed, especially proteins. In a 1996 report (Jeffers) from the United States, the most common allergens were beef, chicken, chicken egg, cow milk, wheat, soy and corn. In this report 80% of the dogs reacted to just one or two items although there are reports of dogs allergic to as many as nine food items. Additional published reports will list fish, rice and potato as foods known to cause adverse reactions. The food items most commonly known to cause ARF in cats include chicken, fish and dairy products. A few minutes spent reading ingredient labels of most commercial cat foods will show these are the most common ingredients used in formulating the diets.
One common misconception by clients and many veterinarians is that food allergy is more likely to develop only after a recent diet change. In fact when food allergies develop the offending allergen has often been fed for over two years, and some patients will eat the same protein for many years before the allergy develops. To further complicate the workup of a suspect food allergic patient is the recognition that some patients will have cross reactions between related food ingredients. This phenomenon is well recognized in human medicine as well. Examples include patients allergic to chicken who will not tolerate duck or turkey. Some patients allergic to beef will cross-react or show clinical signs when exposed to other ruminants, such as lamb or venison. Fortunately not all food allergic patients will have cross reactions, but some will, which further complicates the workup of these patients
Food hypersensitivity in dogsNo age or sex predisposition is known to exist regarding the development of food allergy in the dog, but as many as 50% of food allergic patients may exhibit clinical signs at less than a year of age. There may be a higher rate of food allergy in "allergic breeds" such as Cocker spaniel, Springer spaniel, Labrador retriever, Miniature schnauzer, Shar Pei, West Highland white terriers, Wheaten terriers, German Shepherds, and Golden retrievers. Three breeds of dogs this author associates with a higher rate of food allergy are German Shepherds, Rhodesian ridgebacks, and the Shar Pei dog. Clinical signs are variable but nonseasonal pruritus, otitis, and dermatitis are frequently seen in dogs suffering from a food allergy. Sometimes the clinical signs are as simple (or vague) as recurring pyoderma or a nondescript keratinization disorder (seborrhea). Food allergy should always be considered as a cause for any patient with recurring urticaria, and eosinophilic vasculitis has also been associated with ARF.
In general the clinical signs of food allergy are non-seasonal, although they could be episodic if due to sporadic treat administration. It is also possible for the effects of a food allergy to be low or subclinical (below a pruritic threshold) and only with the addition of environmental allergens will the patient flare.
Any dog with a non-seasonal pruritic dermatosis should have food allergy ruled out as a contributing cause of the skin disease. In addition there are several other clues which may raise the index of suspicion that a patient is suffering from a food allergy. One is the pattern of skin disease. Food allergies are known to commonly affect the "ears and rears" of the patient. Another potentially useful clue is the response to corticosteroids. Atopic dermatitis is usually responsive to corticosteroids at anti-inflammatory doses. While some patients with a food allergy will be very steroid responsive, some will not, and when the pruritus is not steroid responsive, food allergy should be considered. Nearly half of this authors patients will have gastrointestinal manifestations of their ARF. Dramatic GI signs include vomiting and diarrhea, but it may be as subtle as flatulence or frequent (more than 2/day) bowel movements. Rarely reported clinical signs of ARF include seizures and respiratory signs including bronchitis, rhinitis and chronic obstructive pulmonary disease, all of which have been recognized by this author.