Dermatological Disorders

Food Trials in Dogs: Updates and Communication Tips

Galia Sheinberg

MVZ, ESP, DLACVD

Dermatologia Especializada Centro Veterinario México

Mexico City, Mexico

Q. Why should veterinary teams consider performing food trials? What is necessary before initiating the trial?

A. A diagnostic food trial is commonly used when managing canine patients with dermatological or gastrointestinal problems. Patients with cutaneous adverse food reactions (CAFRs) can manifest in various ways, and a thorough clinical history should always include all aspects of the patient’s health. For example, when a patient is presented with skin disease, the clinician should always include gastrointestinal-associated questions; otherwise, important clues with diagnostic value can be missed.

Canine CAFRs manifest primarily with non-seasonal pruritus, otitis, and secondary infections: bacterial pyoderma and Malassezia. Some patients will also present with gastrointestinal problems such as chronic or recurrent diarrhea (up to 80%), flatulence, vomiting, poor fecal consistency, increased number of bowel movements, and eating grass. Dogs can start presenting with symptoms very young, often before 1 year old, but older dogs may also develop the condition.^1,2

Pet owners will seek help at different moments, sometimes when secondary infections have developed or when the problem has become more prominent; this is why a good clinical history is so important. Clinicians must keep in mind that symptoms of CAFRs and environmental allergies are clinically indistinguishable.

Q. What is necessary to help a client be successful during a food trial?

A. Food trials are still considered the gold standard for the diagnosis of CAFRs. Although there is a myriad of available tests on the market, based on available studies, none have been proven to be consistent and sensitive enough to use for clinical diagnosis and these tests should not be used.³

If a food trial is to be successful, client education, communication, and follow-up in the form of messages, calls, and visits are all essential components. Pet owners should be well informed on why a diet trial is needed, what it consists of, and the length of the process; and they should be involved in diet selection. Having a motivated and well-informed client will make all the difference in correctly implementing and harnessing this process’s diagnostic value. Do not proceed when a client is unable to do the trial and, in those cases, proceed with symptomatic control or environmental diagnosis.

Having practical tools to inform and educate owners can be very helpful; providing written information, short videos, and links can expedite the process. This information can be reviewed at home and as many times as needed. 

Q. What diets can be used during food trials?

A. Diet selection can also be a sensitive point for many owners. Veterinarians should work with them to gather sufficient feeding history and preferences to recommend the right diet choice; acceptance by the owner and the pet is essential.

A hydrolyzed or amino acid-based diet is the best commercial diet choice, reducing the chance of using a protein that has previously been fed. Commercial veterinary therapeutic novel protein diets can be considered, but choosing the correct “novel” protein can be difficult. Limited client recollection of previous diets and the possibility of allergen cross-reactivity, undeclared ingredients, and ingredient quality issues are important considerations, especially with well-pet diets.^4,5 Home-prepared diets are also an alternative for some owners. A veterinary nutritionist should be consulted when using a home-prepared diet, as these are not complete and balanced unless adequately formulated.

Q. What are other ways to be successful at performing food trials?

A. Regarding the length of the diet trial, most dogs with CAFRs will respond to the diet by eight weeks. New studies suggest an alternative to make the process easier and increase compliance is prednisone or oclacitinib at the beginning of the dietary elimination trial.⁶ Depending on the patient’s needs and response, these medications are stopped two to four weeks into the diet trial to evaluate if pruritus returns. In the case that it does not, a diet challenge can be performed as early as four weeks. Careful communication and follow-up are necessary in all diet trials but critical when deciding to challenge and understanding what to do if pruritus returns. 

Finally, treating and resolving any secondary infections (skin and ears) and using appropriate flea prevention in all patients undergoing a dietary trial for CAFRs are critical. If these are not addressed, those patients can continue with pruritic behavior, complicating the possibility of a potential food-responsive solution.

1. Olivry, T., & Mueller, R. S. (2019). Critically appraised topic on adverse food reactions of companion animals (7): Signalment and cutaneous manifestations of dogs and cats with adverse food reactions. BMC Veterinary Research, 15(1), 140. doi: 10.1186/s12917-019-1880-2
2. Mueller, R. S., & Olivry, T. (2018). Critically appraised topic on adverse food reactions of companion animals (6): Prevalence of noncutaneous manifestations of adverse food reactions in dogs and cats. BMC Veterinary Research, 14(1), 341. doi: 10.1186/s12917-018-1656-0
3. Mueller, R. S., & Olivry, T. (2017). Critically appraised topic on adverse food reactions of companion animals (4): Can we diagnose adverse food reactions in dogs and cats with in vivo or in vitro tests? BMC Veterinary Research, 13(1), 275. doi: 10.1186/s12917-017-1142-0
4. Fossati, L. A., Larsen, J. A., Villaverde, C., & Fascetti, A. J. (2019). Determination of mammalian DNA in commercial canine diets with uncommon and limited ingredients. Veterinary Medicine and Science, 5(1), 30-38. doi: 10.1002/vms3.125
5. Olivry, T., O’Malley, A., & Chruszcz, M. (2022). Evaluation of the theoretical risk of cross-reactivity among recently identified food allergens for dogs. Veterinary Dermatology, 33(6), 523-526. doi: 10.1111/vde.13110
6. Fischer, N., Spielhofer, L., Martini, F., Rostaher, A., & Favrot, C. (2021). Sensitivity and specificity of a shortened elimination diet protocol for the diagnosis of food-induced atopic dermatitis (FIAD). Veterinary Dermatology, 32(3), 247-e65. doi: 10.1111/vde.12940