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Food allergies in dogs and cats and how to manage them

Dogs and cats can suffer from different types of adverse food reactions. Adverse reactions to a food group fall into different categories: food intolerances or food allergies. These occur when specific ingredient(s) within the diet trigger local irritation within the gut (intolerance) or a more generalised immune response which, in addition to the gut can cause symptoms in other parts of the body e.g. skin, ears, eyes. Since the symptoms of both food intolerances and allergies overlap a differentiation is rarely made, so we will consider them as one for the purposes of this article. In this article our vet explains the causes, symptoms, diagnosis and management for food allergies.

This article was written by a FirstVet vet


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What causes food allergies in dogs and cats?

A food allergy is an inflammatory or immune-mediated response to a specific ingredient or multiple ingredients within the diet as it passes through the stomach and intestines. These ingredients can be proteins, carbohydrates, additives (dyes, flavours, preservatives) or any other molecule that is present in the diet, and narrowing these down to identify the offending ingredient can be tricky. It is not known exactly what triggers the body to develop these inappropriate responses, but once they have developed, they can be lifelong.

What are the symptoms of a food allergy in dogs and cats?

The main symptoms of a food allergy are associated with irritation of the gut and include:

  • Diarrhoea

  • Vomiting

  • Flatulence (wind)

  • Poor body condition or weight loss

  • Poor coat condition

  • Poor appetite

Some food allergies can present as skin allergies and are called ‘cutaneous adverse food reactions’ (CAFR). Symptoms of CAFR include: itchy skin, paws and ears (sometimes only one ear!), red skin, scabby skin, hair loss, ear and skin infections.

Most dogs or cats develop food allergies and begin showing symptoms as young adults (between 12 months and 4 years of age).

How do I find out which ingredient is causing the problem?

An elimination diet trial is the gold standard and most reliable way of diagnosing which diets are causing the food allergy. If your dog or cat has recurrent episodes of vomiting and diarrhoea, or itchy red skin, which appears to be triggered by diet, or in the absence of other medical conditions, your vet will likely recommend an elimination diet trial for 6-8 weeks. While on an elimination diet, you must avoid feeding any other food or treats to your dog.

The three different types of elimination diet:

  • A commercial complete balanced hydrolysed diet. A hydrolysed diet means a protein source that has been broken down (hydrolysed) to very small components which the body does not recognise as an irritant. Examples include but are not restricted to Royal Canin Hypoallergenic, Hills z/d, Purina Hypoallergenic.

  • A commercial complete balanced diet with a single novel protein i.e a protein your dog has never been exposed to, for example salmon, duck, venison

  • A home-cooked balanced diet with a single protein and single carbohydrate. If home-cooking a diet it is important to consult your vet or a licensed veterinary nutritionist to make sure you are providing a complete balanced diet for your pet and do not cause them to become deficient in important nutrients.

Most vets will recommend trying a hydrolysed diet first, and only if your dog or cat refuses to eat the hydrolysed diet consider a diet with restricted nutrients. This is because a hydrolysed diet has no molecules in it that resemble food molecules and therefore has the best chance of success. The other diets may still contain ingredients that your dog may react to.

How do I manage a food allergy in the long term?

If your pet’s symptoms have resolved or greatly improved while on an elimination diet, it is very likely that a food intolerance or a food allergy was the cause.

If this is the case, long term management can achieved by:

  1. Continuing to feed the elimination trial diet long-term. Commercial complete hydrolysed diets are likely to be balanced and are good diets to use long-term in adult dogs and cats. If your pet is less than 12-18 months of age, it is important to check the diet is appropriate for growth. Home-cooked diets with restricted nutrients are often not appropriately balanced and are not ideal for long-term feeding. You could either switch to a commercial diet with similar base ingredients, or speak to a veterinary nutritionist who can assist you in balancing your home-cooked diet. Many people find long-term home-cooked diets expensive and labour intensive, but as long as they are balanced they can be used.

  2. Finding out which ingredients caused the intolerance or allergy with a diet challenge. This involves introducing ingredients from the old diet to the diet and monitoring your pet’s reaction. A flare up can take a few days to two weeks and suggests an intolerance or allergy. Stop feeding this ingredient and continue on the elimination diet until symptoms resolve. Then move onto the next ingredient and repeat the process. The main ingredients to test are protein, carbohydrate and grain.

Once you have found a diet that is well balanced for long-term use, that your dog or cat eats well and that does not trigger any gastrointestinal or dermatological symptoms, you have achieved your end goal.

What role does allergy blood testing play?

Although blood tests are available, studies have shown they can be variable and unreliable. Food allergy blood tests investigate the levels of immune molecules called immunoglobulins in your pet’s blood against different food molecules. A high level of immunoglobulins against a food molecule suggests the body is mounting an immune response that is likely to cause allergy symptoms. However, it is not uncommon for blood tests to show false positives, i.e a positive or high result for ingredients that in reality do not cause a problem, or false negatives i.e a negative or low results do ingredients that in reality do cause a problem - for example a food causes a local reaction in the gut (intolerance) but not a fill allergic response (allergy). However despite this, it can still be a useful guide for making elimination diet selections.

Allergy testing is much more reliable for dermatological cases caused by environmental allergens, for example when grass causes itchy skin.

In conclusion food intolerances and food allergies can be frustrating for owners and their pets, and they take a methodically consistent approach to manage. You will need to commit to a long-term plan for diagnosis and management. However, the results are rewarding and can help prevent the uncomfortable effects of adverse food reaction and cutaneous adverse food reactions

When to see your vet

  • Ongoing diarrhoea and/or vomiting

  • Poor body weight or weight loss

  • Poor coat condition

  • Inappetence (Anorexia)

  • Itchy red skin


Further reading

Diarrhoea and vomiting in dogs

Skin allergies and itching in dogs

How to do a food trial for a dog

Cutaneous adverse food reactions

Get help with a first assessment!

If you are unsure whether you need to seek help for your cat or are worried about another reason, you can book a conversation with a vet at FirstVet for advice and an initial assessment.

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