Food Allergies.


drawing of classic canine food allergy lesions
The classical canine food allergy lesion distribution includes signs of


(only some of the above signs are usually present in a given animal; not necessarily all).
 

YOUR PET'S ITCHY SKIN

Itchy skin in the small animal is often more than just a minor annoyance.  Red, oozing bald patches, rashes, and large expanses of hair loss are unfortunate markers of very real discomfort for which a cause should be sought and specifically dealt with.

The food allergy is one of the itchiest conditions known to cat and dog. Animals eat a variety of processed food proteins, fillers, and colourings which are further processed inside their bodies. Proteins may be combined or changed into substances recognized by the immune system as foreign invaders to be attacked. The resulting inflammation may target the GI tract or other organ systems but, in dogs and cats, it is the skin that most often suffers from this immunologic activity.

Many people erroneously assume itching due to food allergy requires a recent diet change of some sort. In fact, the opposite is true.

Food allergy requires time to develop; most animals have been eating the offending food for years with no trouble.

WHAT KIND OF ALLERGY?

Sarcoptic mange and inhalant allergy (also known as "atopy") are the two conditions which must be distinguished from food allergy as the treatment approach to each is markedly different.  Much time and money can be wasted pursuing the wrong the problem.

Please consider the following clues which contribute to pointing us towards the food allergy as a diagnosis. Your pet demonstrates:


WITHOUT ANY POSITIVE CHANGE.
 


A SEASONAL PROBLEM.
 


TO CORTISONE-TYPE MEDICATIONS.
 


CHANGES OFTEN ASSOCIATED WITH ALLERGY OR,
MORE SPECIFICALLY, FOOD ALLERGY.
 


FOR FOOD ALLERGY (see illustration at top of page).

Any of the above findings or observations warrant pursuit of food allergy.

Please note that three of the above four criteria relate to what you, the owner, observe at home. Trouble results when the veterinarian must speak to different family members about the pet and there is disagreement in their observation of the pet at home. It is best to have one person, preferably the one who has the most contact with the pet, be the spokesperson and make the relevant judgments.

graphic: No Fleas!THE FLEA FACTOR: Some animals have many allergies. It would not be particularly unusual for an animal with a food or inhalant allergy to also be allergic to flea bites, especially considering that flea bite allergy is an extremely common allergy among pets. Because allergies "add" to each other, it is possible that a food allergic dog will not itch if its fleas are controlled. Since new technology has made flea control safe and convenient, it is especially important (and no longer difficult) to see that fleas are not complicating a pet's itching problem.

ENSURE IMMACULATE FLEA CONTROL FOR ANY ITCHY PET!


HOW TO DEAL WITH THE FOOD ALLERGY SUSPECT:
THE HYPOALLERGENIC DIET TRIAL

THE BASIC PRINCIPLE:

To determine whether or not a food allergy or intolerance is causing the skin problem, a "hypoallergenic diet" is fed for a set period of time. If the pet recovers, the original diet is fed for up to two weeks to see if itching resumes. If we see recovery with the test diet and itch with the original diet, then food allergy is diagnosed and the pet is returned to either the test diet or another appropriate commercial food indefinitely.

WHAT IS A GOOD HYPOALLERGENIC DIET?

There are two approaches to this question. Obviously, the test diet must be of a food source that the patient could not possibly be allergic to. The traditional method is the use of a “novel” protein and carbohydrate source; that is, something the pet has never eaten before. In the past, lamb has been the protein source of choice as American pet food companies had traditionally failed to produce lamb-based pet foods. Unfortunately, recent production of lamb and rice-based foods have removed lamb from the "acceptable hypoallergenic diet" list.

Fortunately, many pet food companies have discerned the need for diets using unusual protein & carbohydrate sources with a minimum of additives. Foods can be obtained based on venision and potato, fish and potato, egg and rice, duck and pea, and even kangaroo. Our hospital generally recommends duck and potato based foods for dogs and duck and pea based foods for cats.  We have chosen these products because they are available both as canned as well as dry formulas.  (Most pet owners prefer to feed a combination of dry and canned food.)
 
 

It is important that during the diet trial no unnecessary medications be given.  No edible chew toys (such as rawhides or bones) should be given. Treats must be based on the same food sources as the test diet.  (Beware of Rice cakes, though, as wheat is commonly used as a filler.) Chewable heartworm preventives should be replaced with tablets.

Home cooking was originally the only option felt to be appropriately free of allergens but for most animals these special commercial foods are adequate. Occasionally home cooking ends up being necessary after all.
 

The Hydrolyzed Protein Method

Recently a new approach has been introduced using diets made from “hydrolyzed proteins.” This means that a conventional protein source is used but the protein is broken down into molecules too small to excite the immune system. There are three such diets currently marketed:

Hill’s Z/D and Ultra Z/D diets

CNM HA (“HA” stands for “hypoallergenic”) - from the prescription diet division of Purina.

Exclude - made by DVM dermatologics. This product is purchased in powder form to be mixed with water to achieve the desired consistency.

HOW LONG TO FEED THE TRIAL DIET
 

In the past, four weeks was thought to represent a complete trial period.  More recent work has shown that some food allergic animals require eight to ten weeks to respond.  This may be an extremely inconvenient period of time for home cooking. Our current recommendation calls for a recheck appointment or phone call after four weeks of diet trial and then again after eight weeks of trial. Eighty percent of food allergic dogs will have responded to diet trial at least partially by six weeks.  The Labrador retriever and cocker spaniel appear to require up 10 weeks of trial diet before showing a response.  Some animals may even require a longer period.
 
 

WHAT TO DO IF THE DIET IS SUCCESSFUL?

To confirm food allergy, return to the original food; itching resumes within 14 days generally if food allergy was truly the reason for the itchy skin. Many people do not want to take a chance of returning to itching if the patient is doing well; it is not unreasonable to simply stay with the test diet if the pet remains free of symptoms.

It is possible to more specifically determine the identity of the offending foods after the pet is well. To do this, a pure protein source (such as cooked chicken, tofu, wheat flour or any other single food) is added to the test diet with each feeding. If the pet begins to itch within two weeks then that protein source represents one of the pet’s allergens.  Return to the test diet until the itching stops and try another pure protein source. If no itching results after two weeks of feeding a test protein, the pet is not allergic to this protein.

WHAT TO DO IF THE DIET IS UNSUCCESSFUL?

Generally, an unsuccessful food trial is strongly suggestive that an inhalant allergy is really the primary problem but there are some other considerations that should at least be mentioned:  .Are you certain that the dog received no other food or substances orally during the trial? Was sarcoptic mange ruled out?  Your pet may require a longer diet trial.  Are you certain regarding the factor which pointed us toward the food allergy? If your pet has not been biopsied, now may be a good time. If an inhalant allergy has risen to the top of the list, symptomatic relief either via medication, special baths, or allergy shots will likely be necessary.  Chronic itchiness can be extremely uncomfortable and prompt relief is our goal as well as yours.