Adverse food reactions (AFR) encompass food intolerances as well as immunologically mediated hypersensitivities, that is, food allergies, and may occur in companion animals. As there is no cure for food allergies today, it is of utmost importance to identify the causative allergens and pathophysiological mechanisms (functional changes in the body) in order to develop adequate preventive measures and treatment strategies.

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The true prevalence of food allergy in dogs and cats is unknown. In dogs with clinical signs suggestive of food induced allergic dermatitis (FIAD), the prevalence of AFR (including immunological and non-immunological conditions) was reported to range between 7.6% and 25%, and AFR were diagnosed in 1.69% of the total canine population presented to a veterinary teaching hospital over 12 months. The prevalence of AFR in cats ranged from 0.22% to 6% of animals with cutaneous and from 17% to 22% with gastrointestinal tract signs.

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Risk Factors

Factors influencing oral tolerance are the integrity of the intestinal epithelial barrier, tolerance‐inducing antigen‐presenting cells (APC), and T‐regulatory cells. The known risk factors for atopic dermatitis are the same in humans and in companion animals and are also associated with a higher risk for food allergy.

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Clinical Signs

Companion animals may spontaneously develop skin, respiratory (only cats), and gastrointestinal tract reactions due to food intolerances. However, there is no clear evidence of an association between AFR and respiratory symptoms in companion animals, where AFR generally manifest as cutaneous (FIAD) or gastrointestinal tract abnormalities. In dogs, cutaneous symptoms are commonly reported and are frequently indistinguishable from those of canine atopic dermatitis due to environmental allergens. Generalized or localized non-seasonal pruritis (itching) of the face, ears, paws, axillae, inguinal, and perineal regions is the most frequently described dermatological sign. Otitis externa (ear infection) and recurrent pyoderma (superficial bacterial infection) with or without itching have also been associated with AFR in canines.

Clinical signs reportedly develop between 4 hours and 14 days after eating the offending food and suggest that more than one pathophysiological mechanism is involved. Gastrointestinal tract signs may include vomiting, diarrhea, weight loss, and abdominal discomfort. Between 10% and 30% of cats with AFR show cutaneous and gastrointestinal tract symptoms.

The most common food allergen sources for dogs are beef, chicken, milk and dairy products, and lamb. For cats, important food sources evoking AFR are beef, chicken, and fish.

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Diagnosis

Firstly, a thorough diagnostic work‐up is indispensable in companion animals to distinguish type I Hypersensitivity (allergy) from other AFR (Type IV Hypersensitivity) in order to choose the appropriate food allergen avoidance diet, which is the only cure for food allergy. A food diary may be helpful.

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Second, a skin prick test or prick‐to‐prick test with native food is performed. These detect food allergy with high sensitivity, although specificity is rather low at 50%. It should be acknowledged that the risk of false‐positive results may result in unjustified dietary restrictions.

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The third cornerstone of diagnosis is food antigen‐specific IgE in serum. In dogs and cats with suspected AFR, IDT reactivity to food antigens and food‐specific IgE are not reliable and therefore not recommended. Repeatability, sensitivity, and specificity of food‐specific IgE have been unsatisfactory. This may be due to the lack of IgE involvement in canine AFR.

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If diagnosis cannot be confirmed with the previously mentioned measures, the next possibility is using an elimination diet to further assess AFR. During an allergen‐free dietary period, symptoms should subside over several weeks. Consequently, AFR in cats and dogs are diagnosed by feeding an elimination diet with a novel protein for ≤8 weeks. In improved situations, re-challenge with the original diet should lead to clinical deterioration. Patients should subsequently improve again during elimination diet, with gastrointestinal tract signs often subsiding before concurrent dermatological problems.

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During the elimination diet, the pet must not receive any other food, treats, medications (under close veterinary supervision), vitamins, or supplements with any protein other than the one chosen for the diet. In animals, anaphylactic episodes are rarely observed. Management of AFR in dogs and cats currently also relies on avoidance of the offending food. Also, flavored medications, treats, or supplements may contain soy, pork, and beef. Finally, taxonomic relationship between meat sources should be considered to avoid the risk of cross‐reactivity (poultry, domestic ruminants, large wild game, etc).

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Elimination Diet

A food elimination diet is the most accurate way of identifying food allergens and providing relief for dogs and cats. An elimination diet will be necessary for 8 weeks, up to 13 weeks in acute cases, in order to identify food allergens. Because clinical signs can take between 4 hours and 14 days to present themselves, a single protein source should be fed up to 14 days as long as no new symptoms manifest and current symptoms do not become worse.

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Within 2-3 weeks on the single protein source the animal should show significant improvement in clinical signs. Evidence has shown that by 5 weeks in dogs and 6 weeks in cats after starting an elimination diet more than 80% of companion animals have achieved remission of clinical signs of adverse food reactions.

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The most common food allergen sources for dogs are beef, chicken, milk and dairy products, and lamb. For cats, important food sources evoking adverse food reactions are beef, chicken, and fish. During the elimination diet, the pet must not receive any other food, treats, medications (under close veterinary supervision), vitamins, or supplements with any protein other than the one chosen for the diet. Kefir should be avoided as it is a milk product. Taxonomic relationship between meat sources should be considered to avoid the risk of cross‐reactivity (poultry, domestic ruminants, large wild game, etc).

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*It is recommended that Omega-3 be supplemented during the elimination by Krill Oil or Squid Oil. Avoid using any fish oil until fish has been ruled out as an allergen. Refer to our Fish Oil file for dosage*

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Begin by keeping in mind any suspected and/or common proteins as being an allergen. Do not use these during the elimination diet. Once the 8 week period is complete, suspected proteins can be reintroduced in order to determine if they are indeed an allergen. If possible source novel proteins to begin the elimination. Novel refers to a new protein that has never been introduced or any protein that has not been fed in over 8 weeks and which no known allergies to it are suspected. Liver, secreting organs, and RMBs can be fed during the elimination diet as long as they are all from the same protein source. Avoid eggs unless they come from the animal being introduced. Stop feeding any protein at the first signs of an adverse reaction.

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Week 1-2

• Feed only one protein that is not suspected to be an allergen to begin introducing the novel protein.

• Begin with slowly introducing just the meat and bone until the meal is entirely the new protein. If successful begin introducing liver followed by secreting organs. Eggs can now be fed if applicable.

• Only move forward once poop is well formed.

• Feed the new protein 14 days as long as there are no new signs or current signs worsen.

• If new signs develop or current ones worsen within 4 hours to 14 days, the protein is considered to be an allergen. Stop feeding it and choose another protein.

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Week 3-4

• With no signs of an adverse reaction it is safe to introduce another protein in the same manner as above. Meat and bone until the entire meal has been replaced with the new protein then liver and secreting organs.

• Feed the new protein 14 days as long as there are no new signs or current signs worsen.

• If new signs develop or current ones worsen within 4 hours to 14 days, the protein is considered to be an allergen. Stop feeding it and choose another protein.

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Week 5-6 and 7-8 will be done in the same manner.

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Once 3-4 proteins have been successfully introduced, meaning no clinical signs are present, the elimination diet can be deemed successful. More proteins can now be introduced to allow for more variety in the diet. Suspected food allergens may be reintroduced over 14 days in an attempt to accurately identify them as food alergens.