Food allergy

From Dog
Food allergy-induced otitis externa[1]

Food allergy is a common nutritional disease of dogs characterized by skin diseases after ingestion of food allergens.

Adverse reactions to food consist of two different responses: immune-mediated and non-immune-mediated. The disease caused by the former is called food allergy and is a type-IV hypersensitivty reaction[2], whereas the latter reaction is recognized simply as food intolerance. Food allergy in dogs causes clinical signs such as chronic dermatitis with pruritus, vomiting, and diarrhea, and it is difficult to diagnose because the clinical signs in skin is similar to those of canine atopic dermatitis[3]. To distinguish food allergy from atopy, the allergens involved must be identified at the onset of clinical signs[4]. In dogs, these allergens may include one or multiple items such as gluten, food additives (such as coloring, flavor enhancers and preservatives) or high levels of certain proteins.

Despite the entry of food allergens via the intestinal tract, in the majority of dogs clinical symptoms are usually associated with the skin (e.g. atopy)[5], although acute respiratory disease (e.g. asthma) and lymphocytic-plasmacytic enteritis may also occur less commonly and is rarely as severe as what occurs with humans that may have severe, life-threatening anaphylactic responses to certain food groups (e.g. peanuts[6]).

Allergen-induced T cells are thought to be involved in initiation of the cutaneous symptoms, and the presence of fermentation byproducts of dietary protein digestion (especially ammonia, phenol, indole, short-chain fatty acids, branched-chain fatty acids and valerate) play a role in initiating allergic responses in dietary sensitive breeds[7]. Although IgE levels have been shown to drop in food-allergy sensitive dogs, the lymphocyte populations appear responsible for regulating the long-term food-allergy response[8].

In some dogs, food allergy is a result of frank dietary mineral and vitamin deficiency, especially in young dogs fed home-made food preparations[9].

Clinical signs in affected dogs are usually skin-related or intestinal-related symptoms such as pruritus around the head and trunks, secondary otitis externa, pododermatitis, chronic intermittent and refractory diarrhea (especially colitis).

Diagnosis is one of exclusion. Other causes of pruritus and intestinal signs include environmental allergens (e.g. dust mites, pollen, topical applied or ingested chemicals, certain skin preparations, shampoos, etc) as well as skin parasites (e.g. flea-allergy dermatitis, Dirofilaria repens[10], Demodex spp, Sarcoptes spp, Malassezia spp), pyoderma, cutaneous lymphoma and lupus erythematosus. Skin scrapings, skin cultures and skin biopsies are recommended in most cases.

When all other possibilities have been excluded, patch testing has been employed using allergen-specific serum IgE and IgG antibodies to attempt to identify possible triggering allergens which may vary between dogs[11]. The usefulness of patch testing has been controversial[12].

Treatment involves dietary exclusion trials (elimination diet) aimed at introducing the dog to a novel protein source (e.g. lamb with rice) for a test period, usually 4 - 6 weeks, and once successful, then reintroducing other dietary components until or if dermatological symptoms reappear. An elimination diet trial followed by food provocation has been regarded as the standard for diagnosis of food allergy, however, the cumbersome nature of the elimination diet trial makes it difficult to accomplish.

In many dogs, desensitization to specific allergens within the food may not be reduced and long-term therapy with elimination diets may be required to prevent relapses in cases with skin-related food allergy[13]. In dogs with chronic idiopathic enteropathies, response to an elimination trial is frequently observed and only a fraction of them relapse after a dietary challenge[14].

In severe or chronic cases, oral prednisolone may be required to modulate the pruritic response and long-term antimicrobials may be necessary if secondary bacterial infections with Staphyloccus pseudintermedius is evident. Other drugs such as astaxanthin (a carotenoid) have shown promise at alleviating clinical signs in food allergy cases[15].

Antipruritic medicated shampoos may help to minimize secondary bacterial and yeast infections[16].


  1. Vetnext
  2. Ishida, R et al (2004) Lymphocyte blastogenic responses to inciting food allergens in dogs with food hypersensitivity. J Vet Intern Med 18:25–30
  3. Olivry, T et al (2007) Food for thought: pondering the relationship between canine atopic dermatitis and cutaneous adverse food reactions. Vet Dermatol 18:390–391
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  9. Becker N et al (2012) Calcium deficiency: a problem in growing and adult dogs: two case reports. Tierarztl Prax Ausg K Kleintiere Heimtiere 40(2):135-139
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  12. Olivry, T et al (2007) Food for thought: pondering the relationship between canine atopic dermatitis and cutaneous adverse food reactions. Vet Dermatol 18:390–391
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  16. Schilling J & Mueller RS (2012) Double-blinded, placebo-controlled study to evaluate an antipruritic shampoo for dogs with allergic pruritus. Vet Rec 171(4):97