Itch, itch, scratch, scratch. Does your dog lick at his
paws, rub his belly on the floor or have chronic
ear infections? Many people
assume that dogs and cats with itchy skin have an allergy to ingredients in
their food – but actually food allergies in pets are less common than
environmental allergies to pollens, molds or dust mites. It can be tricky to
differentiate environmental allergies (termed atopic dermatitis) from food
allergies, but sometimes atopic dermatitis can present as skin conditions that
occur seasonally, while food-allergies are more typically year-round (although
not all animals follow these patterns).
Some cats and dogs present with diarrhea that resolves with
a change in diet. In these cases, it is more likely that the animal is responding
to differences in fat, fibre and digestibility of the food, rather than to a
specific ingredient. In fact, “adverse food reactions” can be divided into two
categories: food allergies and food intolerance.
- Food allergy involves an immune-response to specific proteins in the food. Signs can include gastrointestinal signs (vomiting, diarrhea) or – more commonly – skin problems (itching, redness, infections).
- Food intolerances do not involve the immune system, and can contribute to gastrointestinal symptoms or – less commonly – skin issues. An example of food-intolerance includes lactose-intolerances, which rarely occurs in dogs and cats, but is common in humans.
How can we diagnose
food allergies?
A strict elimination diet is a good way to reliably diagnose
a food allergy or intolerance. The new diet needs to be fed exclusively for 6-10 weeks (with no
additional treats, table scraps, rawhides or dental chews), then the animal can
be re-challenged with the original diet.
Choosing an elimination diet can be difficult. Exotic
ingredients such as lamb, duck and venison are not always good, especially if a
dog has been exposed to these ingredients in the past. Unfortunately many pet
foods are introducing new and exciting ingredients that sound healthy, which
actually complicate matters when trying to rule-out food allergies.
Finding novel ingredients requires a thorough diet history –
including all pet foods, treats, table-scraps, etc. It is important to find
novel meat and carbohydrate sources, as carbohydrates can contain allergens as well. A
proper elimination diet should contain one protein and one carbohydrate source,
plus all the vitamins and minerals required to make the diet complete and
balanced.
An alternative option to novel ingredient diets is a hydrolized
diet. These diets contain proteins that have been chemically or enzymatically
hydrolyzed to reduce them to a smaller size that is less likely to trigger an
allergic reaction.
Many over-the-counter pet foods boast the benefits of their
novel protein diets meant for food allergies. However, in many cases these
diets still contain more than one protein and carbohydrate source, either
intentionally or through unintentional contamination from other food lines made
in the same manufacturing plant. A true hypoallergenic diet should be created
in a facility with strict cleaning protocols, and should always be the first
diet manufactured to decrease the risk of contamination. Furthermore,
hydrolized diets are not available in over-the-counter recipes. It is possible
to use over-the-counter diets as a management diet once a food-allergy is
diagnosed, but should not be used during the strict elimination diet period to
diagnose a food allergy.
What about grain-free
or gluten-free diets?
While there has been a lot of marketing talk lately
regarding a movement to grain-free options for dogs and cats, in reality grains
are less common causes of allergies than animal products. The most commonly
reported food allergies in dogs are beef, dairy, wheat, chicken and egg; in
cats beef, dairy and fish are more common culprits. See our next blog in the
nutrition series for more about grain-free diets.
In humans there are medical conditions (e.g. celiac disease)
that cause people to be sensitive to gluten, a protein portion of some plants.
It is currently a popular trend towards pet-foods labelled as gluten-free.
However, gluten-sensitivity has only been reported in a small, related family
of Irish Setters, and never in cats. There is no evidence to support that
gluten-free diets have any health benefit in the majority of dogs and cats.
While food allergies do occur in dogs and cats,
environmental allergies and food intolerances are more commonly the causes of
skin and gastrointestinal problems. If you are concerned about the possibility
of food allergies for your pet, you need to consider a proper food-allergy diet
trial done under the supervision of your veterinarian.
Vanessa Tonn, DVM
Bowmanville Veterinary Clinic
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