An adverse food reaction (AFR) is any clinically abnormal response due to the ingestion of food or food additives, it is classified as a food allergy (immune-mediated response to a food) or food intolerance (abnormal physiological response to food with no immunological basis).¹ Some dogs with AFR are presented with signs at a young age and have both dermatologic and gastrointestinal (GI) signs. Adverse food reactions should be considered likely in dogs with non-seasonal pruritus, otitis externa and/or perianal pruritus and concurrent signs of GI disease including soft feces, intermittent diarrhea, flatus or frequent defecation. The most commonly reported food associated with ARF in dogs is beef, followed by dairy products, chicken and wheat (Figure 1).² A clinical diagnosis of AFR in an individual patient requires consistent clinical findings, thorough diet history, and resolution of signs after exclusive feeding a novel or hydrolyzed protein food.

Diet History

A thorough diet history is critically important for diagnosis and effective management of AFR. It provides clues about the underlying cause of the patient's clinical signs, including those consistent with ARF or other causes such as seasonal pruritus due to environmental allergies. It is important to ask owners about all sources of foods including dog walkers/pet sitters, toddlers, grandparents, and other individuals who have contact with the pet. It is frequently helpful to allow the owner to complete the diet history form at home so it's as accurate as possible when recording foods and treats given. Specific and open-ended questions are encouraged when taking a diet history to ensure that the owner feels comfortable sharing openly and honestly. For example, it may be useful to ask "What treats does your pet get when s/he comes in after going to the bathroom?" rather than, "Does your pet get any treats?" When owners feel that it is assumed their pet receives treats they are more likely to share openly.

An effective dietary elimination trial hinges on a complete diet history so that an appropriate food may be identified for the trial and all other foods may be addressed with the owner. The diet history is made easier by using a standardized template such as the Short Diet History Form found at www.wsava.org/nutrition-toolkit.

Figure 1. Ingredients reported to cause adverse reactions in 330 dogs are shown2 Beef, dairy, chicken, and wheat are most common in published cases of adverse reactions to food or food ingredients.

Selecting Foods for a Dietary Elimination Trial

An appropriate food for a dog undergoing an elimination trial contains a single, novel (new to that particular dog) or hydrolyzed protein source identified based on that dog's unique diet history. Many commercial and therapeutic novel and hydrolyzed food options exist. Whether a novel or hydrolyzed therapeutic food is chosen for a particular pet undergoing an elimination trial should depend on the diet history, owner and pet preferences, concurrent conditions, as well as response to therapy.

Novel Protein Foods

The rationale for using a novel protein food to which the dog has not been previously exposed during a dietary elimination trial for food allergy is that an immune response to a food component can only occur if the dog has previously been in contact with the offending food allergen. There is nothing intrinsically hypoallergenic about novel proteins; they are simply used because they are novel to the allergic pet's immune system. For this reason, commercial therapeutic novel protein pet foods ideally contain one intact protein that is not commonly eaten by pets. These foods are typically highly digestible and therefore also appropriate for dogs with a food allergy resulting in gastrointestinal (GI) signs, and contain a limited number of ingredients to limit possible antigenic exposure.

Commercially available novel protein foods have documented benefits in dogs with chronic, non-seasonal pruritic dermatitis.³ In a prospective, multi-center clinical study, 2 novel protein foods with salmon or venison and enhanced concentrations of omega-3 fatty acids and antioxidants were fed for 8 weeks to dogs with suspected ARF and/or atopic dermatitis. A total of 74 dogs from primary care veterinary practices across the United States completed the study. Veterinary assessment revealed significant improvement over time for dogs receiving both foods and pet owners also reported significant improvements in clinical signs (face rubbing, scratching, licking, head shaking, ear scratching, skin redness, hair loss, and skin and coat condition) over time.

Hydrolyzed Protein Foods

Hydrolyzed therapeutic pet foods contain one protein source that has been hydrolyzed (broken down) to polypeptides <10,000 Daltons in size, reducing their potential to be allergenic. In theory, this results in a protein that cannot accommodate cross linking of IgE receptors on mast cells, which are necessary for mast cell degranulation and initiation of an immune response to an offending antigen in an allergic pet. There are some advantages of using hydrolyzed therapeutic foods. Because it is the protein size (rather than its novelty) that prevents an immune response, a protein can be fed to which the pet has been previously exposed. This can be of particular use in pets that have been adopted and obtaining an accurate diet history is often impossible. Hydrolyzed foods are also highly digestible, which may be beneficial for some pets with GI signs due to AFR.

A commercially available therapeutic chicken hydrolysate food was useful for the diagnosis of AFR in dogs with non-seasonal pruritus when fed exclusively at least 6 weeks.⁴ This retrospective study included 63 dogs with non-seasonal pruritus (n=59) or ear disease (n=4) that were evaluated at an academic referral practice (Royal Veterinary College, United Kingdom). A total of 46 dogs completed the feeding trial and 30 dogs (65%) had improvements in pruritus and clinical scores. Of these 30 dogs, 22 had improvement in pruritus, which recurred after challenge with their original food indicating that an AFR was likely causing their clinical signs. Concurrent GI signs were reported in six dogs with AFR; GI signs resolved in all dogs after feeding the therapeutic food and recurred in five dogs when challenged with their original food. Overall, 19 of 21 dogs (90%) with concurrent GI signs had complete resolution of their clinical signs during the dietary trial.

Dietary Trials - Tips for a Successful Outcome

A recent review of available evidence found that when an elimination diet trial was followed closely, >90% of dogs and cats with cutaneous AFR responded by 8 weeks.⁵ Regardless of outcome, strict adherence to an exclusive elimination trial for at least 8 weeks provides invaluable information that may be used to identify the underlying cause of pruritus and help manage clinical signs. Client-education is likely the single most important component of a successful elimination trial for dogs with suspected AFR. Owners need to understand the basic underlying cause of an AFR and importance of feeding the recommended elimination diet exclusively.

They should be cautioned that even minimal exposure to other foods (treats given by a friend or occasional kibbles of another pet's food) could potentially cause misinterpretation of the results of their pet's elimination trial. Prior to beginning a dietary food trial, owners should be counseled on substitutions for flavored medications, supplements and preventatives currently being administered - these may affect the pet's response during a food trial. It is important for owners to educate other individuals that have contact with the pet; they should be aware of the pet's food restrictions during the trial and about alternatives if treats are given. Although undoubtedly challenging for the family of a pet undergoing an elimination trial, it is important to recognize that no other currently available diagnostic test is able to accurately diagnose AFR.

Long-Term Management

To confirm a diagnosis of AFR, a re-challenge or provocation is necessary after the elimination diet trial is completed. In reality, many pet owners are satisfied with improvement that occurs during an elimination trial and decide to continue feeding the elimination diet indefinitely versus a dietary provocation trial. In these patients, it's important to re-introduce any new foods/treats or favored medications/toothpastes one at a time so the potential allergenic item can be more easily identified.

References

1.  Jackson HA. Food allergy in dogs - clinical signs and diagnosis. Eur J Comp Anim Pract. 2009;19:230–233.

2.  Roudebush P. Ingredients and foods associated with adverse reactions in dogs and cats. Vet Dermatol. 2013;24:293–294.

3.  Fritsch DA, Roudebush P, Allen TA, et al. Effect of two therapeutic foods in dogs with chronic nonseasonal pruritic dermatitis. Intern J Appl Res Vet Med. 2010;8:146–154.

4.  Loeffler A, Lloyd DH, Bond R, et al. Dietary trials with a commercial chicken hydrolysate diet in 63 pruritic dogs. Vet Rec. 2004;154:519–522.

5.  Olivry T, Mueller RS, Prelaud P. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res. 2015;11:225.