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, flavorings, and colorings 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
Allergic skin disease and its secondary infections dominates small animal practice. Pets can be allergic to insect bites (fleas are not inherently itchy unless the pet is allergic to flea bites), airborne proteins (such as molds, pollens, and dust mite parts) or foods. Pets can (and often do) have multiple allergies adding together to make them itchy. The skin infections that come from scratching perpetuate the itching. To solve the problem, the infection must be cleared up and the offending allergen(s) removed from the pet's world.
There is controversy about how common food allergy is in dogs and cats. Some experts feel it is relatively rare while others feel is much more common than we realize. It is hard to tell because there is no simple test for food allergy and the skin lesion distribution is difficult to distinguish from that of airborne allergy which is frequently concurrent in the same patient.
So what are our clues that a pet has a food allergy?
There are several hints and here they are:
Any of the above findings or observations warrant pursuit of food allergy.
Please note that several of the above 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.
ENSURE IMMACULATE FLEA CONTROL FOR ANY ITCHY PET!
For more information on flea biology and flea control, click here (our flea control center)
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.
There is no other way to determine if a pet has a food allergy. Blood tests are not useful.
Before reviewing diet strategies for this process, here are some additional concerns:
Blood tests for allergy can detect antibodies against certain food proteins but this does not necessarily mean the pet has an allergy. It may mean nothing more than the pet has eaten that type of protein before. These tests are not valid for determining if a pet has an allergy against a certain type of food.
So let's review how to choose an appropriate test diet.
WHAT IS A GOOD HYPOALLERGENIC DIET?
Novel Protein Diets
Examples of novel protein diets
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 sourse; 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 for most pets.
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 venison and potato, fish and potato, egg and rice, duck and pea, and even kangaroo. Diets used for diet trials must contain basically one protein and one carbohydrate source and neither can be something the pet has had before. Recently several diets that include duck, venison etc. have been released to the general market. Be aware of foods that contain these ingredients because these ingredients will not be useable for future diet trials if they used as the pet's regular 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. Occaisionally home cooking ends up being necessary after all. Recipes for appropriate diets can be purchased through www.balanceit.com, a web site set up by the American College of Veterinary Nutrition.
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:
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 only one food allergic dog in four will respond within this time frame and that a more appropriate trial period would be 10-12 weeks. 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 longer trials.
All commercial diets mentioned have a 100% guarantee.
This is especially helpful for feline patients,
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. Often it is difficult to remember 10-12 weeks later how itchy the dog used to be before the diet trial. The diet challenge helps make it more obvious whether the diet trial has worked or not.
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?
Assuming secondary skin infections have been controlled, 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:
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.
Click here for information on symptomatic relief of itching
Click here for information on inhalant allergy
Click here for information on sarcoptic mange
Click here for information on yeast infections in the skin
See a veterinary nutritionist's thoughts on Food Allergy Trials in Dogs.
For treats appropriate to dogs on a food trial see:
Other acceptable products include those made of pig parts: ears, snouts etc.
Page last updated: 1/17/11