International Science Symposium : Nature , Nurture , and the Case for Nutrition Diagnosis of Adverse Reactions to Food in Dogs : Efficacy of a Soy-Isolate Hydrolyzate-Based Diet 1 , 2

Adverse reactions to food include allergy (reaction with an immunological mechanism) and intolerance (nonimmunological reactions, including idiosyncratic, metabolic, and toxic responses) (1). Adverse reaction to food results in dermatological (pruritus, otitis externa, seborrheic dermatitis, recurrent bacterial or fungal dermatitis) and in 10% of cases in gastrointestinal (diarrhea, abdominal discomfort) signs (2). Food sensitivity is one of the most common causes of nonseasonal allergic skin disease in dogs. A diagnosis of adverse reaction to food is confirmed by elimination-challenge tests (1,3). The elimination period involves feeding the dog a specialized diet; the diet must include all common foodstuffs and incorporate novel ingredients to which the dog has not had prior exposure. An improvement in clinical signs during this period indicates the likelihood of an adverse food reaction. The elimination period is followed by a challenge with the dog’s usual diet, and if symptoms return, this confirms the diagnosis of adverse food reaction. Because they are easily customized and assumed to be free of food additives, homemade diets have been recommended by veterinary dermatologists for the diagnosis and management of adverse reaction to food. Although food additives have been linked to adverse reaction in humans, a similar link has yet to be established in dogs and cats (1). A homemade recipe is custom designed so that it provides the dog with novel sources of protein, carbohydrate, and fat. However, owners are often reluctant to feed homemade diets because they are time consuming to prepare, expensive, and might be unpalatable (4). The noncompliance is high (4). In addition, achieving a nutritionally balanced diet using a homemade recipe can be challenging. Commercially available elimination diets have been marketed for some time (3), utilizing a range of protein sources not normally found in standard dog diets. Such diets are cost effective, convenient, and nutritionally complete, but are not truly hypoallergenic because they contain whole proteins to which the dog may or may not have had prior exposure. This may have contributed to the apparent poor performance reported for some of these diets (5). A strategy for reducing allergenicity involves hydrolyzing the protein source with enzymes. Food allergens are usually glycoproteins, with the most common ranging in size from 14 to 40 kD (6), although smaller (10 kD) and larger (70 kD) molecules can be immunogenic (1). They are usually stable despite heating, pH, or digestive enzymes (7). By enzymatically breaking the protein down into smaller peptide fragments it becomes intrinsically less allergenic and more digestible. This latter point is probably of great importance, because if a dietary protein is properly digested before contact with the gastrointestinal mucosa, it will not activate the immune system. In a study of veal calves, a soy hydrolyzate diet was utilized more efficiently, and was less immunogenic than a diet containing intact proteins (8). This strategy was also used successfully in babies with allergies to cow’s milk (9). The purpose of this study was therefore to assess the efficacy of a diet containing soy isolate hydrolyzate for the diagnosis of adverse reaction to food in dogs in a multicentric field study.