Diet trials useful in diagnosing canine itching

Diet trials have proved successful in diagnosing food allergies, but veterinarians must be educated on their availability and use

By Don Vaughn •  Royal Canin

Frequent itching in dogs is one of the most common dermatological issues seen by veterinarians. Left untreated, it can be distressing to pets and owners alike, and potentially lead to more serious health issues.

Itching can have a variety of causes, notes a 2018 State of Pet Health Report from Banfield Pet Hospital, including fleas, scabies, and other parasites, and environmental allergens such as pollen, mold, and household cleaning solutions. Food allergies affect just 0.2 percent of dogs, the Banfield report notes – but experts say they can be the most difficult to diagnose and treat. One helpful tool in the veterinarian’s toolbox is Royal Canin Ultamino®, a diet specially prepared for dogs with food sensitivities.

The symptoms of a food allergy frequently mimic the symptoms of other types of allergies, notes Megan R. Painter, DVM, DACVD, a board-certified dermatologist with Angell Animal Medical Center in Waltham, Massachusetts. The most common include scratching, ear shaking or scratching, and excessive paw licking.

“Making an accurate diagnosis of a food allergy can take a lot of time because there are a lot of manifestations of canine allergy,” Dr. Painter observed in a recent podcast with Update. “The most challenging part is confirming that the dog has allergies. and you know what is driving that allergy. You don’t want to miss anything.”

Taking a detailed history is vital, and Dr. Painter says she spends at least 10 minutes just talking to the owner about their pet’s specific issues. “I want to know when the issues started,” she says. “Was the dog 6 months old? Two years old? Do you notice seasonality? Is there anything that you feel flares your dog up? The history is an essential part of any allergic work-up because you want to know the patterns, if any.”

While allergies are a frequent source of skin issues in dogs, there are many others that veterinarians should also keep in mind, Dr. Painter says. “It’s important to pay attention to your signalmen,” she notes. “If you’re looking at a 2- to 8-year-old with issues, that’s different than if you’re looking at a 15-year-old dog with new problems. And when you’re looking at the age of the dog, comorbidities the dog may have and other medications it is on are essential when creating a differentials list for some kind of skin manifestation.”

Reactions to food are immunologic or nonimmunologic. An example of a true immunologic reaction would be the immediate hypersensitivity seen in children with a peanut allergy. “We don’t see this happen commonly in dogs,” Dr. Painter says, “but when we do it’s usually the patient who presents to the E.R. with recurrent hives and diarrhea. But true IGE hypersensitivity driven by food in dogs is not very common, which is why we don’t have blood or skin tests for food allergens in dogs.”

An important indicator that canine itching may be due to food allergies are recurring gastrointestinal issues such as soft stools and a greater frequency of defecation, Dr. Painter notes. “If you get a dog that is coming to you every August but is clinically normal for the rest of the year, it’s probably not a food allergy,” she says. “But if you have a dog that’s continuously pruritic, always having ear infections, always licking its paws, and has soft poop all the time, that dog is food-allergic until proven otherwise.”

At that point, Dr. Painter says, a diet trial may be the most accurate way to confirm a food allergy. “I prefer the term diagnostic diet trial,” she notes. “What we’re trying to do is determine the percentage of the problem that is driven by food. If we can say 100 percent of a dog’s problems went away because we fed him a particular diet, great, we just nailed it. But if they’re not 100 percent better, there might be some variability there, which can be difficult to pick up.”

The client plays a significant role in a diet trial because they must give the prescribed food for a period of weeks and record any noticeable changes in their dog’s behavior that may suggest it’s working. This can be problematic, Dr. Painter says, because the client may not return for rechecks, or be unable to afford the cost of the food and office visits.

“I believe a lot of veterinarians worry that it’s going to be hard for pet owners to do, and that’s actually a very valid worry,” Dr. Painter notes. “My research conducted during my residency looked at adherence to diet trials, which is basically the pet owner’s ability to follow through on the recommendation to be strict because the main rule for the diagnostic diet trial is that it’s an 8-week diagnostic test in which they’re feeding their pet one food very strictly. You don’t want a lot of treats or pill pockets being given, or the patient eating the other’s dog’s food. There are a lot of barriers that could get in the way of someone performing the diet trial to a diagnostic standard. I think a lot of veterinarians worry that they won’t be able to coach pet owners appropriately.”

Dr. Painter encourages veterinarians to have “some language in their back pocket” when talking to pet owners about a diet trial. Owners should be questioned about how they are going to give medication during the trial, and their plan for feeding other dogs separately.

“Veterinarians need to remember that these are other human beings who have their own barriers and issues and schedules that could make a diet trial difficult,” Dr. Painter says. “That’s not a problem, we just need to talk about it. Having these conversations can take time for a veterinarian, but they also can help make it so that when we recommend a food trial, we are recommending it for a reason, and feel good about that recommendation.”

A variety of veterinary diets are available for diet trials. Dr. Painter recommends hydrolyzed food over whole protein food. “In my opinion, the benefit of hydrolyzed food far outweighs the potential benefit of a novel protein,” she says. “Novel protein was the way things were before hydrolyzed foods came to market and were heavily developed for dogs. What we would do was take a thorough diet history and say, it looks like this dog has had chicken and beef, so I’m going to select a rabbit-based diet. That should be novel to the immune system and less likely to cause a reaction. And in some cases that would be correct. You might be able to make a diagnosis using a whole protein diet or a novel protein diet.

“However, there’s the potential for cross-reactivity between proteins, which means there could be some proteins that rabbits and chickens share. This could mean your diagnostic diet trial will not be diagnostic because of cross-reactivity; you have the potential sensitization to whatever that whole protein was. And that’s going to make it so the dog still looks like it has allergies, because it does. It’s still allergic to whatever that whole protein was.”

The use of hydrolyzed foods removes the potential for cross-reactivity, Dr. Painter notes. “We have incredibly sophisticated hydrolyzed foods available to us in veterinary medicine,” she says. “Hydrolysis is the process by which we change the size and chemical structure of a protein to make it less antigenic, to make it less reactive and immune systems less likely to care about it. The reason for that is because it’s smaller, or we’ve disrupted the epitope, which is the lock-and-key that the immune system binds to, creating an immune reaction. Hydrolyzed foods create less of an immune response as a result of the fact that the food is less antigenic.

Many veterinarians turn to Royal Canin Ultamino®, a veterinary-exclusive dry dog food for adult dogs with food sensitivities needing a short-term elimination diet or long-term nutrition. This innovative diet is the result of years of extensive research, formulated as a nutritional solution for pets with severe food sensitivities. Its clinically proven and highly palatable formula contains a protein source that is broken down to an amino acid level, so it can be absorbed in the digestive tract a with reduced risk of triggering a food sensitivity.

Royal Canin Ultamino® contains optimal amounts of B vitamins and amino acids which reinforce a dog’s skin barrier. Omega-3 fatty acids EPA and DHA help promote healthy skin and coat, Royal Canin notes, and an exclusive blend of fibers helps support healthy digestion in dogs prone to digestive upsets, including diarrhea. With strict manufacturing procedures to help avoid cross-contamination, pet owners can confidently feed Royal Canin Ultamino® long-term to dogs with food sensitivities.

Diet trials have proved successful in diagnosing food allergies, but many veterinarians aren’t well educated on their availability and use, Dr. Painter observes. “Even when I was in school, some of my mentors did not believe that food allergies were a problem,” she says, “so this is something that really takes getting in with someone who is very keen on diet. It’s an area that I love because there’s nothing more satisfying than helping a dog come off medication, not have infections, and have normal poop because I switched one thing, and that was their food. It’s a wonderful diagnosis to make. About 25 percent of patients will respond to a diet trial. It’s worth it to the animals who have been suffering from this condition and may have been misdiagnosed for years.”

Dr. Painter offers an online course for veterinarians interested in learning more about how to diagnose and treat allergic dogs. For information, visit


*Megan R. Painter, DVM, DACVD, a board-certified dermatologist with Angell Animal Medical Center in Waltham, Massachusetts. Quotes and information from podcast.



* (Itching and Allergy in Dogs)

This Education Center article was underwritten by Royal Canin.

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