Dog Food for Allergies
The diets vets use to diagnose and manage food allergy in dogs according to the Merck Veterinary Manual - novel-ingredient elimination diets and hydrolyzed-protein diets, fed strictly for up to 3 months - and three hydrolyzed prescription diets compared on what their makers publish.
AI illustration This is a reading guide to published veterinary information and to what makers state on their own pages. A food trial is planned with your vet: Merck says to consult your veterinarian for a specific test plan for your dog.
The short answer: no everyday food fixes an allergy. For a dog with a suspected food allergy, a diet is first a test and then a long-term answer. The Merck Veterinary Manual describes two options:
- An elimination diet of ingredients the dog has never eaten before.
- A prescription diet with hydrolyzed proteins, broken down so the dog’s body no longer recognizes them.
Merck adds that blood and skin tests are not reliable for diagnosing food allergy. Food allergies are also less common than airborne allergies, so many itchy dogs need something other than a new food. Our dog allergies guide covers the other causes.
How the Food Trial Works
From Merck:
- Strictly one diet. Nothing else for the whole trial: no treats, no table food, no flavored medicines, not even toothpaste. One previously fed ingredient can make the trial fail.
- Up to 3 months. If the itch clears markedly or completely, a food allergy is suspected.
- The check. The old food goes back in. If the signs return, usually within 1 hour to 14 days, the allergy is confirmed.
- The culprit. Single old ingredients are then added back one at a time, each for up to 14 days, to find the cause. The foods dogs are most often allergic to are beef, chicken, eggs, corn, wheat, soy and milk.
- Long term. Once the cause is known, strict avoidance is the control.
Three Hydrolyzed Diets Compared
| Diet (dry) | Protein source | What the maker states | Protein | Energy | Source |
|---|---|---|---|---|---|
| Hill’s Prescription Diet z/d, Hydrolyzed Chicken Flavor | Hydrolyzed chicken liver and chicken (first ingredient: corn starch) | “Highly hydrolyzed proteins that are broken down to avoid detection by the immune system”; no intact animal protein | Hill’s gives dry matter: 20.1% | 348 kcal per cup | Hill’s |
| Purina Pro Plan Veterinary Diets HA Hydrolyzed, Chicken Flavor | Hydrolyzed protein; single carbohydrate source | Protein “broken down into small components to be less likely to cause an adverse food reaction” | 18.0% min, as sold (moisture 11% max) | 315 kcal per cup | Purina |
| Royal Canin Veterinary Diet Hydrolyzed Protein HP | Hydrolyzed soy protein (first ingredient: brewers rice) | “Low molecular weight peptides”, highly digestible; EPA and DHA for the skin | 19.0% min, as sold (moisture 10.5% max) | 324 kcal per cup | Royal Canin |
How we put this together. The hydrolyzed dry diet of each of the three main veterinary diet makers, compared on what each maker states on its own page, checked on 26 October 2026. Hill’s gives protein on a dry-matter basis, without water. Purina and Royal Canin give it for the food as sold, so the numbers do not line up directly. All three are sold through vets or with a prescription, so there are no shop links. Which one fits depends on what your dog has eaten before, which is a question for your vet. We have not fed these diets. Hill’s also sells d/d diets made with potato and salmon, venison or duck.
Over-the-Counter “Sensitive” Foods
Everyday foods sold for sensitive skin or stomachs are a different kind of product from prescription hydrolyzed diets. The three we compared list salmon, chicken or chicken by-product meal first, and chicken is on Merck’s list of the most common food allergens. For a diagnostic food trial, follow your vet’s choice of diet. Our page on food for dogs with sensitive stomachs compares three of them.
