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How to do a food trial for a dog

Food trials are performed in dogs for both diagnostic and treatment purposes. A food trial can be performed to help establish if your dog has a food sensitivity, a food intolerance or a food allergy to something in their diet. Common signs of a food sensitivity, food intolerance or food allergy can include diarrhoea, vomiting, itchy skin, itchy paws, hair loss, ear infections, skin infections or a skin rash. Read our advice here.

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A food trial involves feeding your dog a special elimination diet advised by your vet, for a set period of time, during which your dog should not be allowed to eat anything else. For a diagnosis to be confirmed, there must be improvement of the symptoms when the original diet is withdrawn and return of the symptoms after feeding this diet again. If your dog improves during the food trial, long-term feeding of an appropriate diet is a very effective treatment.

What food can I use for a food trial?

Care is needed when choosing an elimination diet for your dog’s food trial as some commercial products can have cross-contamination with potential allergens, which will therefore affect the outcome of the food trial. There are 3 main diet options:

1. A veterinary diet with limited ingredients (single novel protein diet): A novel protein is one that your dog has never eaten before. Options could include pork, rabbit, venison, duck, kangaroo and fish (for example salmon, cod, capelin).

These are complete and balanced diets. They are generally palatable and appropriate for long-term feeding.

2. A veterinary diet with hydrolysed protein (some hypoallergenic diets): These are complete and balanced diets, in which the protein source has been broken down into small peptides or amino acids that are too small to be detected by the immune system and consequently cause any reactions. These diets are appropriate for long-term feeding and highly digestible but the palatability can be variable. An example of a hydrolysed diet is Purina Pro Plan Veterinary Diets Canine Hypoallergenic HA. This diet contains hydrolysed soya as the protein source and is formulated for dogs of all life stages including puppies. Therefore, it is suitable for nutritional management during growth and maintenance.

3. A complete and balanced home-cooked diet: This can be made using one novel protein source and one novel carbohydrate source. These can be very palatable and digestible. However, unless the recipe is formulated by a veterinary nutritionist, it is likely that it will be incomplete and unbalanced. This could lead to nutritional deficiencies, toxicities and other health effects.

What about treats/chews/supplements during a food trial?

The smallest amount of any potential allergen could cause a reaction. It is therefore very important to try and avoid all potential triggers during your dog’s food trial. All treats, animal-based chews, dental chews, supplements, probiotics, toothpastes etc. should be avoided. Note that some medications, for example some flavoured oral parasite medications, may contain animal protein in the formulation, in which case they should be avoided. Ask your vet about this if you are unsure.

No scavenging or hunting should be allowed. To avoid this, use of a short lead, constant supervision and, occasionally, a muzzle may be required. If your dog accidentally eats something other than the elimination diet, make a note of what and when, and monitor for any symptoms.

During your dog’s food trial, normal treats may be substituted with a small amount of the elimination diet food. Many dogs consider any food given outside normal meal times as a treat, therefore this should keep them happy during their food trial.

What should I give my dog to drink during a food trial?

You should only offer your dog plain water to drink during the food trial. Nothing should be added to the drinking water and your dog should not be allowed to drink milk, as this may affect the food trial.

How long should I continue a food trial?

There are 3 to 4 phases of a food trial. The length of each phase will vary depending on the symptoms and how quickly these resolve. If your dog suffers mainly with gastrointestinal signs (diarrhoea and/or vomiting), positive results could be seen as quickly as 2 to 3 weeks. If your dog suffers with itchy skin, the food trial may need to be continued for 5 to 12 weeks.

How to perform a food trial

Phase 1: feed strictly only the elimination diet for up to 12 weeks, until resolution or satisfactory reduction in the symptoms. During this phase, your dog should not be given anything else orally, other than water to drink. It can be beneficial to keep a diary to record your dog’s symptoms each day.

Phase 2: re-introduce the original diet, along with any usual treats, chews, supplements, toothpaste etc. and monitor for a return of the symptoms. If there is a food sensitivity, a food intolerance or a food allergy, symptoms may recur within 2 to 3 days. However, they can also take up to 2 weeks to return. It is important only to give a very small amount of the original diet, as sudden dietary changes can cause an upset tummy in many dogs irregardless of whether they have a food intolerance.

Phase 3: once symptoms have recurred, return to feeding strictly only the elimination diet. If the symptoms resolve again, this confirms a food sensitivity, a food intolerance or a food allergy. This could take 2 to 4 weeks.

If the elimination diet is appropriate and balanced for your dog, it can be continued long-term. Alternatively, you and your vet may decide to proceed to Phase 4, to identify the specific ingredients that cause the symptoms.

Phase 4: continue feeding the elimination diet, while offering previously fed ingredients as treats. One ingredient at a time should be offered for up to 2 weeks, starting with a protein as these are the most common triggers. If there is no return of the previous symptoms, this ingredient is safe to continue feeding. However, if there is a flare up, this ingredient should be avoided.

Reasons the food trial may be unsuccessful

  • Environmental allergens or atopic dermatitis

  • Flea allergic dermatitis

  • Uncontrolled secondary skin infection and/or parasitic infestation

  • Poor compliance

  • Unreliable diet formulation or preparation (food contamination) or inappropriate choice of novel protein source

When to see your vet

  • Any vomiting, ongoing diarrhoea or soft stools

  • Uncontrolled itchiness of the skin, paws and/or ears

  • Sore skin, a skin infection or a skin rash

  • Hair loss

  • Recurring ear infections

Further information

Diarrhoea and vomiting in dogs

Food sensitivities/intolerance/allergies

Cutaneous adverse food reactions

Skin allergies and itching in dogs

Still have questions?

Book a video appointment to have a chat with one of our FirstVet vets for advice, treatment, and if necessary, referral to your local vet.

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