Updated April 12, 2021
Elsewhere on this site we’ve published the evidence for which foods dogs and cats are allergic to. Now we’ll show you how to figure it out for your own pet. This even works for a mouse!
Diagnosis of Food Allergies
The bad news is that there is no simple test. Popular blood test kits are not reliable enough.
The good news is that you can do it at home. It’s called an elimination diet. You have two choices:
- Buy one off-the-shelf
- Make it yourself (this is preferred if possible, see below)
Note: if you give any other food item, even tiny scraps or flavourings, you could ruin the test. You should place your pet where they can’t hoover up table scraps, crumbs or kitchen waste especially around mealtimes. Keep the dishwasher closed and supervise animals when outside. Other pets in the house are best fed on the same diet if there’s any chance of cross-contamination.
Commercial Elimination Diets
In Australia, both Hills Pet Nutrition, Royal Canin and Prime100 sell elimination diets. Purina options are also available in other countries.
Which ever you choose, it’s best to only use one. This is especially true for Anallergenic, which is currently our preference.
Food Allergy Diets for Dogs
- Hill’s Prescription Diet d/d Potato & Venison Formula – canned & dry
- Hill’s Prescription Diet z/d – dry
- Royal Canin Hypoallergenic – canned & dry
- Royal Canin Anallergenic – dry
- Prime100 SPD kangaroo & pumpkin or crocodile & tapioca – loaf
Food Allergy Diets for Cats
Whether you make or buy it, it is essential that every cat in the house on the same elimination diet. It is impossible to prevent exposure to a degree that will stop the symptoms completely. For example, water shared between cats is likely to become contaminated with microscopic food particles.
- Hill’s Prescription Diet d/d Venison & Green Pea Formula – dry
- Hill’s Prescription Diet z/d – canned & dry
- Royal Canin Hypoallergenic – dry
- Royal Canin Anallergenic – dry
- Royal Canin Gastrointestinal (pouches- this isn’t truly an elimination diet but I’ve included it as it works well for many cases of IBD)
Bold = in stock at Walkerville Vet (the rest can be ordered)
Home-Made Elimination Diets
The home-prepared diet is considered the gold standard elimination diet. Although commercial alternatives from your vet are easier, we always recommend at least starting by trying to do it yourself. Here’s how you do it…
Step 1: Understand the theory
This is a giant test to see if your dog or cat is allergic to part of their existing diet. Therefore, if we design a diet with NO previously used ingredients there should be no reaction. You can’t be allergic to something your body has never encountered.
You have to make a simple diet entirely out of ingredients your dog or cat has never eaten. Your diet won’t be balanced but if your pet is adult, in good health and not pregnant, no harm should occur over the trial period.
Step 2: Make the diet
For dogs, choose one meat and one carbohydrate source at a proportion of 1:2 or 1:3. Ingredients might include one of: [goat, camel, rabbit, kangaroo, fish species] plus one of: [pumpkin, sweet potato, potato, tapioca] etc. By all means, cook it in batches to save time. Turkey and duck may be best avoided due to possible cross-reaction with chicken allergy.
For cats, just choose one meat source from the above list and there’s no need to cook. It’s a lot easier. However, only use meats fit for human consumption. The meat needs to be 100% pure, with nothing else packed on the same equipment without cleaning.
Step 3: Never, never compromise
This is the critical thing: the immune system is the most sensitive detector we know. It can’t be fooled. There’s no point in doing an elimination diet until every member of the household is on the same team and agrees to avoid treats or accidental food access.
Step 4: Run the test for long enough
For skin problems, it takes 8 weeks before 90% of food-allergic dogs and cats will have improved. By this time, if your pet is still itchy or unwell, the cause is unlikely to be a food.
For gastrointestinal problems, the response is typically more rapid. I expect to see some results within 2 weeks.
If they are getting better, you still have more to do…
Step 5: Rechallenge the original diet
The real test is this: do the skin or gastrointestinal problems return when they go back to the old food? Otherwise the improvement might have been due to something else. If you get a worsening after rechallenge, your pet most likely has a food allergy. The next step is to find out to what…
Step 6: Identify the allergen(s)
Put them back on the elimination diet until they are better again. Now, a week at a time, add back one individual ingredient (such as beef, chicken, wheat, dairy) until your pet starts reacting to one of them. There could be more than one.
Step 7: Design a lifelong diet
Once you know the offending ingredient, the problem is usually that it will be found in all pet foods at some level. Choices are:
- Find a mainstream limited ingredient diet
- Make your pet’s food yourself
- Use the veterinary diets listed above (e.g. when you go on holidays)
Remember, home made elimination diets aren’t balanced enough to use beyond 8 weeks. You need to either find a commercial alternative that is tolerated or get nutritional advice on how to construct a balanced diet.
If you got this far, well done; you’re on the home stretch now.
If your diet trial failed, don’t despair. It’s probably not the food but there’s so much more your vet can do.
You might also like: The myths about food allergy in dogs.
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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These articles are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!