• Most common food allergies in dogs are to beef, dairy and wheat, but may be any dietary ingredient, especially proteins. Other allergens reported include pork, chicken, milk, egg, fish and soy. One study has suggested that food allergy may account for up to 10% of all allergic disease (Scott, 1978) while the prevalence of food allergy in non-seasonal allergic skin disease has been estimated at 23% (Reedy & Miller, 1989).
• The relevance of adverse reactions to food for GI conditions may be greater than that for dermatological signs, although these may or may not be allergic (immune-mediated) reactions.
• Allergic breakthrough should also be considered - the clinical signs of an allergic response may only become apparent when some arbitrary threshold of immunological activity is exceeded (Brostoff & Hall, 1996) and a small increase in the total allergen load may therefore be tolerated or be sufficient to break through the allergic theshold and provoke an allergic response.
• Detection of food-specific antibodies in blood sample may indicate hypersensitivity to a specific food Skin: food hypersensitivity ; however, correlation with food trials has not been consistently good.
• Identifying allergens responsible for allergy may aid in selecting a food which avoids these for a food elimination trial Elimination diets for adverse food reactions. The best method is to use a hydrolyzed protein or a protein source not previously fed Dietary diet: for adverse food reaction.
• Recent research has shown that high levels of food-specific IgG may be better predictors of food allergy than IgE levels.
• Several conditions may, in some cases be related to adverse reactions to food, eg gluten-sensitive enteropathy and inflammatory bowel diseases Inflammatory bowel disease: overview such as eosinophilic colitis Colitis: eosinophilic and lymphocytic-plasmacytic colitis Colitis: overview (Simpson, 1985).
• The food allergy dermatological response in dogs is often delayed with up to 6-8 weeks of allergen-free diet to induce remission, and up to 2 weeks to provoke a relapse. This wide range of responses has made the direct connection between the clinical signs and diet more difficult to establish as compared to humans.
• Blood tests for food allergies are no longer recommended as these have been proven to be unreliable. 

Uses

Alone

• The new diet should be fed exclusively for a period of 3-10 weeks. If the clinical signs resolve, the dog should ideally be challenged with its original presenting diet in a provocation test (Simpson et al, 1994). However, while this strategy cannot confirm whether the mechanism responsible for the adverse reaction is a true food allergy or food intolerance (Guilford, 1994), this distinction may not be clinically relevant to an individual animal. Furthermore, many owners are reluctant to have their dogs undergo a food challenge after resolution of signs.

In combination

• With other diagnostic tests in the investigation of a pruritic dog or a dog with a gastrointestinal disorder.

Other points

• Established approach to diagnosis of food allergies is elimination diet of 3-10 weeks followed by provocative diet challenge if signs resolve.
• Allergen testing aims to shorten the period required to make a diagnosis of hypersensitivity.
• Food-allergies commonly co-exist with other hypersensitivities such as atopy Skin: atopy and flea hypersensitivity Skin: flea bite hypersensitivity