Food Allergies In Dogs And Cats

Reactions to food are a major concern to many pet owners. Here’s what we know about food allergies, and which foods cause most of the problems.

What Is A Food Allergy?

Strictly speaking, we call them Adverse Food Reactions, including:

  • Food allergy
  • Food intolerance
  • Non-allergic food hypersensitivity

I’ll keep using both ‘food allergy’ & AFR to mean all these things.

What Does Food Allergy look Like?

Food allergies in dogs and cats cannot be distinguished from other allergies. You need your vet to help you decide whether your pet’s symptoms are due to a food allergy or something else. Dogs and cats usually show a range of symptoms including:

  • Hair loss from the flanks and belly.
  • Itchy faces (with nasty infected scratch wounds in cats)
  • Itchy skin. Especially armpits, groin, ears and feet.
  • Pinpoint skin crusts (miliary dermatitis).
  • Chronic diarrhoea, vomiting or weight loss (follow the links for other causes).
  • Urticaria (‘hives’) & angiooedema (facial swelling)

AFRs appear to start earlier in life and be less responsive to treatment than other allergies. Click here to read about non-food causes of allergy in dogs and cats.

How Common Are Food Allergies?

This is a source of intense debate. I was taught in the early 90’s that AFRs account for around 1% of allergies in dogs. Since then, that number has been steadily rising. We now think that AFRs are present in around one quarter of dogs with allergic disease (Proverbio et al, 2010).

Which Foods Are Dogs & Cats Allergic To?

This table shows a summary of many studies on AFRs in dogs and cats (Mueller et al, 2016). Not all the studies were as strict as others but the general idea looks clear. There doesn’t appear to be a major culprit. Dogs and cats appear to be reacting to the ingredients already found in their foods, such as beef, chicken, wheat, fish and dairy.

I suspect that if we fed dogs on camel and avocado these would end up high on the list as well. Though looking at the rate of reaction to fish and dairy products, I wonder if we should be including these unnatural ingredients in pet foods at all.

Food Allergy In Dogs & Cats
FOOD% OF 297 AFR DOGS% OF 78 AFR CATS
Beef3418
Dairy products174
Chicken155
Wheat134
Soy6
Lamb53
Corn44
Egg41
Pork2
Fish217
Rice2
Barley0.31
Rabbit0.31
Chocolate (!)0.3
Kidney bean0.3
Tomato0.3

Study data used under Creative Commons Attribution 4.0

How Do We Diagnose Food Allergies?

The bad news is that there is no simple test. The good news is that you can do it at home. It’s called an elimination diet.

The home-prepared diet is considered the gold standard elimination diet (Proverbio et al, 2010). You can buy commercial alternatives from your vet called hydrolysed protein diets but we always recommend at least starting by trying to do it yourself. Here’s how you do it…

How To Make An Elimination Diet

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.

Step 2: Build the diet

For dogs, choose one meat and one carbohydrate source in roughly equal quantities. Ingredients might include one of: goat, camel, rabbit, kangaroo, unusual fish species, duck, plus one of: pumpkin, sweet potato, potato, tapioca, etc. By all means, cook it in batches to save time.

For cats, just choose one meat source from the above list and there’s no need to cook. It’s a lot easier. However, never buy ‘pet grade’ meats if they are fed alone, only use meats fit for human consumption. Read why here.

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.

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 or kitchen waste,. Never leave food where they might have access, including that of other pets.

It’s worth also asking about the food source. The meat will need to be 100% pure, with no other other meat packed on the same equipment without cleaning.

Step 4: Run test for 8 weeks

After feeding it for 8 weeks, over 90% of food-allergic dogs and cats will have improved (Olivry et al, 2015). By this time, if your pet is still itchy or unwell, the cause is unlikely to be a food. If they are getting better, you still have more to do… 

Step 5: Rechallenge the original diet

This is the real test; do they get itchy again when they start eating the old food? Otherwise the improvement might have been due to something else. If you get a worsening of itch 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. However, you can choose special veterinary diets, high quality limited ingredient diets, or just decide to make your pet’s food yourself.

Remember, 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.

References

Mueller, R. S., Olivry, T., & Prélaud, P. (2016). Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC veterinary research, 12(1), 1.

Olivry, T., Mueller, R. S., & Prélaud, P. (2015). Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC veterinary research, 11(1), 1.

Proverbio, D., Perego, R., Spada, E., & Ferro, E. (2010). Prevalence of adverse food reactions in 130 dogs in Italy with dermatological signs: a retrospective study. Journal of Small Animal Practice, 51(7), 370-374.

By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on Facebook and Twitter. Like or follow our page or subscribe via email to read the latest.
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