Food Allergies in Dogs

Allergies in dogs seem to have become more and more common over the years. Whether this is just because we are getting better at diagnosing them is debatable, but certainly the pet food manufacturers have had an important role to play in dealing with this phenomenon. Although a food allergy is thought to be non curable, the good news is that with proper diagnosis and management it can be well controlled in virtually 100% of cases.

What is a food allergy?

A more appropriate term for a food allergy is an adverse food reaction. It is where ingestion of a certain ingredient in the diet causes itchiness anywhere on the body and recurring skin or ear infections with Malassezia yeast and bacteria. Food allergies can also cause digestive tract signs too, such as fecal mucus, blood in the stools and increased frequency of defecation. They have also been associated with increased flatulence.

The root cause of these adverse food reactions is unknown, but research points towards an increase in permeability of the gut wall, or a failure of the gut associated immune system. Though it has never been proven that certain breeds are affected worse than others, some breeds do seem to be over represented. The age of onset can range from a few months to 12 years old.

What are the ingredients that dogs are most commonly allergic to?

There are 7 ingredients that are frequently responsible for adverse food reactions:

1. Beef
2. Milk
3. Eggs
4. Chicken
5. Soy
6. Wheat
7. Corn

Statistically, beef and soy are the biggest offenders. Many dogs will be allergic to more than one of these ingredients, and may also be allergic to things in their environment, such as pollen, certain grasses or fleas.

How can a food allergy be diagnosed?

If a dog has had general itchiness that does not lessen in the winter months, recurrent skin and ear infections or intermittent soft stools, it is worth investigating for a food allergy.

There are 3 recognised diagnostic methods:

1. A blood test to measure antibodies to various ingredients.
2. An intradermal skin test where allergens are injected at various points on the skin and the reaction is measured.
3. An elimination diet.

The intradermal skin test is thought to be very inaccurate, and the jury is still out on the blood test. The elimination diet is seen as the most reliable, and the cheapest of the three options. It does however require a motivated and disciplined owner in order to achieve meaningful results.

Elimination Diet

There are three basic elimination diet choices:

1. Home cooked food

This is not generally recommended as it is time consuming for the owner and can also provide an unnatural and nutritionally unbalanced diet. However, if the dog is incredibly fussy and the owner cannot bear to force it to eat a commercial diet, the best ingredients are one of either lamb, fish, duck or turkey, plus one of either rice or potatoes. The two ingredients selected (the former high in protein, the latter a carbohydrate source) should be ones that the dog has preferably never eaten before.

2. A commercial, limited antigen diet

If one of these diets is to be recommended, suitable ingredients would be venison, rabbit or oatmeal. Remember, we are looking for ingredients that your dog has never eaten before, so cannot possibly already be allergic to.

3. A commercial, hydrolysed protein hypoallergenic diet

These contain proteins that have been broken down to the extent that they are no longer capable of causing an allergic reaction. They are often referred to as prescription diets because they are usually purchased via a veterinarian, although they can be obtained over the counter without a prescription. They are significantly more expensive than limited antigen diets, so it is wiser to try a limited antigen diet first as if the elimination diet is successful, the dog will remain on that food for life.

The elimination diet must be given for a minimum of 6 weeks, and possibly up to 10, in order to observe the maximum response. Owners must not give their dog ANYTHING else during the trial period, meaning no titbits, treats or vitamin supplements. For example, many owners do not realize that rawhide chews are made from cow derivatives and that with beef being the most common culprit in allergies, these chews could be the root of the problem. During the trial period, nothing must enter the dogs mouth apart from the chosen diet and water.

If the symptoms in question are intense itchiness, many vets will prescribe antihistamines or steroids during the first few weeks of the trial in order to make the dog more comfortable. If the dog gets better as the trial goes on, and the initial drugs to provide temporary comfort have worn off, then it is suggestive of a food allergy. If this occurs, the dog is then challenged with its former diet to see if the symptoms return and therefore confirm the diagnosis. It usually takes between 3 and 7 days for the symptoms to return after initiating the challenge.

If there is a partial improvement in the dogs condition, it is likely that the dog indeed has a food allergy but also has other allergies at the same time. The dog will then be kept on the elimination diet while other potential allergies are investigated, such as flea bite sensitivity and atopy. These can be checked for via intradermal testing or blood tests.

If a food allergy is confirmed, the owner can either continue to feed the same food given during the elimination trial indefinitely, or can persevere with dietary trials by introducing the 7 most common allergic ingredients (see above) one by one until it is ascertained exactly what the dog is allergic to.