Food allergies account for about 10% of all the allergies seen in dogs. It is the third most common cause after flea bite allergies and atopy (inhalant allergies)
Food allergies generally account for 20% of the causes of itching and
scratching in dogs.
Food allergies plus atopy account for another 20%.
The entire process of a pet being sensitized to a particular agent in food and the complicated
antibody
response that occurs in the intestinal tract in pets with food
allergies are not very well understood. Despite our lack of
understanding of the actual disease process, there are many things that
we do know including the symptoms, how to
diagnose food allergies, and
also how to treat them.
Food allergies affect both dogs and cats. Unlike atopy, there is no
strong link between specific breeds and food allergies. Food allergies
affect both males and females and
neutered
and intact animals equally. They can show up as early as five months
and as late as 12 years of age. Many animals with food allergies also
have concurrent inhalant or contact allergies.
Food allergy or intolerance?
There is a distinction that needs to be made between food allergies
and food intolerances. Food allergies are true allergies and show the
characteristic symptoms of itching and skin problems associated with
canine and feline allergies. Food intolerances can result in diarrhea or
vomiting and do not create a typical allergic response. Food
intolerances in pets would be similar to people who get diarrhea or an
upset stomach from eating spicy or fried foods. Fortunately, both food
intolerances and allergies can be eliminated with a diet free from
offending agents.
Common food culprits
Several studies have shown that some ingredients are more likely to
cause food allergies than others. In order of the most common offenders
in dogs are beef, dairy products, chicken, lamb, fish, chicken eggs,
corn, wheat, and soy. As you may have noticed, the most common offenders
are the most common ingredients in dog foods. This correlation is not a
coincidence. While some proteins might be slightly more antigenic than
others, many proteins are similar in form and the incidence of allergic
reactions are probably associated with the amount of exposure.
Symptoms
The symptoms of food allergies are similar to those of most allergies
seen in dogs and cats. The primary symptom is itchy skin affecting
primarily the face, feet, ears, forelegs, armpits and the area around
the anus. Symptoms may also include
chronic
or recurrent ear infections, hair loss, excessive scratching, hot
spots, and skin infections that respond to antibiotics but reoccur after
antibiotics are discontinued. There is evidence that dogs with food
allergies may sometimes have an increased incidence of bowel movements.
One study showed that non-allergic dogs have around 1.5 bowel movements
per day where some dogs with food allergies may have 3 or more per day.
It is difficult to distinguish an animal suffering from food
allergies from an animal suffering from atopy or other allergies based
on physical signs. However, there are a few signs that increase the
suspicion that food allergies may be present. One of these, is a dog
with recurrent ear problems, particularly yeast infections. Another, is a
very young dog with moderate or severe skin problems. A third tip off,
is if a dog suffers from allergies year-round or if the symptoms begin
in the winter. And the final clue, is a dog that has very itchy skin but
does not respond to steroid treatment.
Diagnosis
The diagnosis for food allergies is very straightforward. But due to
the fact that many other problems can cause similar symptoms and that
many times animals are suffering from more problems than just food
allergies, it is very important that all other problems are properly
identified and treated prior to undergoing diagnosis for food allergies.
Atopy, flea bite allergies, intestinal parasite hypersensitivities, sarcoptic mange,
and yeast or bacterial infections can all cause similar symptoms as
food allergies. Once all other causes have been ruled out or treated,
then it is time to perform a food trial.
Food trials and elimination diets: A food trial consists of
feeding an animal a novel food source of protein and
carbohydrate
for at least 12 weeks. A novel food source would be a protein and
carbohydrate that the animal had never eaten before. Examples would
include be rabbit and rice, or venison and potato. There are a number of
such commercial diets available on the market. In addition, there are
specialized diets that have the proteins and carbohydrates broken down
into such small molecular sizes that they no longer would trigger an
allergic response. These are termed 'limited antigen' or 'hydrolyzed
protein' diets. Homemade diets are often used, as the ingredients can be
carefully restricted. Regardless of the diet used, it must be the only
thing the animal eats for 12 weeks. This means no treats, no flavored
medications, no rawhide or pig's ears; absolutely nothing but the
special food and water. In addition, the dog should not be allowed to
roam, which may result in him having access to food or garbage.
Food Trial Tips
Only the recommended diet must be fed.
Do NOT give:
- Treats
- Rawhides
- Pigs Ears
- Cow hooves
- Flavored medications (including heartworm preventives) or supplements
- Flavored toothpastes
- Flavored plastic toys
- Any type of food when giving medications
If you want to give a treat, use the recommended diet. (Hint: canned
diets can be frozen in chunks or baked, and these can be used as
treats.)
If possible, feed the other the same diet as the patient. If not,
feed other pets in an entirely different location than the patient, and
do not allow the patient access to that food.
Do not allow the dog access to the cat's litter box.
Keep your pet out of the room at meal times. Even a few small amounts
of food dropped on the floor or licked off of a plate can void an
elimination trial and require you to start over. Wash the hands and
faces of any children after they have eaten.
Do not allow your pet to roam. Keep dogs on leashes when outside.
Keep a journal in which you can record the date and any foods, treats, etc. your pet may have accidentally eaten. |
| A food trial consists of feeding a dog a novel food source of protein and carbohydrate for 12 weeks. |
Veterinarians used to recommend that a pet only needed to be placed
on a special diet for 3 weeks but new studies show that in dogs, only
26% of those with food allergies responded by day 21. However, the vast
majority of pets responded by 12 weeks. Therefore, it is very important
to keep the pet on the diet for the entire 12 weeks. If the dog shows a
marked reduction or elimination of the symptoms, then the animal is
placed back on the original food. This is called 'provocative testing'
and is essential to confirm the diagnosis. If the symptoms return after
going back on the original diet, the diagnosis of a food allergy is
confirmed. If there has been no change in symptoms but a food allergy is
still strongly suspected, then another food trial using a different
novel food source could be tried.
| The only way to accurately diagnose food allergies is with a food trial. |
Blood Testing: There is no evidence
that blood tests are accurate for the diagnosis of food allergies.
Veterinary dermatologists insist that there is no merit in these tests
whatsoever in the diagnosis of food allergies. The only way to
accurately diagnose food allergies is with a food trial as detailed
above. While the intradermal skin testing is excellent for diagnosing
atopy (inhalant allergies) it is ineffective for food allergies. While
specialized blood tests can be used to help in the diagnosis of atopy,
they have no benefit in diagnosing food allergies. In our review of all
the current books and articles on veterinary dermatology and allergies,
we could not find a single dermatologist that endorsed anything other
than the food trial as an effective diagnostic aid. If you want to
diagnose and treat food allergies you must do a food trial.
Treatment
The treatment for food allergies is avoidance.Once the offending
ingredients have been identified through a food trial, then they are
eliminated from the diet. Short-term relief may be gained with
fatty acids,
antihistamines, and steroids, but elimination of the products from the
diet is the only long-term solution.The owner of the animal has two
choices. They can choose to feed the animal a special commercially
prepared diet or a homemade diet.
If the owner chooses to feed the homemade diet, then they can
periodically challenge the pet with new ingredients and determine which
ingredients are causing the food allergy. For example, if the animal's
symptoms subsided on a diet of rabbit and potatoes, then the owner could
add beef to the diet for two weeks. If the animal showed no symptoms,
then they could then add chicken for two weeks. If the animal began to
show symptoms, then it could be assumed that chicken was one of the
things the pet was allergic to. The chicken could be withdrawn and after
the symptoms cleared up, a different ingredient could be added and so
on until all of the offending ingredients were identified. A diet could
then be formulated that was free of the offending
food sources.
If homemade diets are used, it is essential that they be balanced,
with correct amount of ingredients, vitamins, and minerals.
Homemade diets for such long term use should be developed by a veterinary
nutritionist.
Be aware that some pets with food allergies may develop allergies to
new foods if they are fed those foods long enough. If you see signs of
food allergies returning, consult your veterinarian.
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