Food allergy or intolerance occurs occasionally in cats and dogs when an ingredient of the diet, usually part of the protein content, causes signs such as itching or diarrhoea. The aim of dietary management is to discover which ingredient is causing the problem and then eliminate it from the pet's diet.

WHAT IS A FOOD ALLERGY
Food allergies are estimated to cause 1% of all skin problems in dogs and cats. Other allergic skin problems, for example allergy to flea bites, are more commonly seen. The incidence of gut upsets, such as vomiting or diarrhoea that are caused by food allergies is not known, but is thought to be greater than 1%. Animals that have both itching and gastrointestinal problems are more likely to have food allergies.

The exact mechanism by which a protein in the diet causes the signs of food allergy is not known. It is thought that abnormal amounts or types of protein particles from food are absorbed into the bloodstream from the digestive tract. This causes antibodies and inflammatory chemicals to be released from cells of the digestive tract and skin (Hypersensitivity).

The skin and digestive tract may then become sensitive to food containing that particular protein ingredient. These hypersensitivity reactions, such as itching, vomiting or diarrhoea, may occur within minutes to hours, or even several days later. The offending dietary ingredient need not be a new one in the diet. Allergies can develop to foods that have been fed for years but the allergy may develop with a sudden onset. Once an allergy has developed, the sensitivity to the ingredient may last a lifetime, so foods containing that ingredient will need to be left out of the diet permanently.

WHICH FOODS CAUSE FOOD ALLERGY?
Any food ingredient that your pet has previously been fed can cause hypersensitivity reactions. The protein part of the food is the most likely culprit. Allergies are therefore seen to commonly feed proteins.

Common Protein Allergens
· Beef · Eggs · Wheat Gluten · Lamb

Some animals will develop diarrhoea when fed milk, although this is described as an intolerance, rather than a true allergy because a hypersensitivity reaction is not involved.

DIAGNOSING FOOD ALLERGY
Skin irritation and scratching can result from other causes, rather than food allergy. Therefore it is important that other causes, such as allergies to fleas, be carefully considered. If your pet's skin damage is severe and is making your pet irritable and miserable, your veterinary surgeon may prescribe anti-inflammatory drugs until the "itch-scratch" cycle is broken.

THE ELIMINATION DIET
Since the offending food is usually one that has been fed to your pet, your veterinary surgeon may ask you to list all the foods in your pet's diet, including treats, bones, chocolates, breakfast cereals etc! From this list, your veterinary surgeon will find foods not previously fed, which can be used to prescribe a nutritionally balanced diet that will be unlikely to cause allergic reactions in your pet - a selected protein diet.

Feeding only the elimination diet for the prescribed time is the diagnostic procedure that best determines if your pet has a food allergy. It may take up to 6 weeks for the itching caused by the allergy to completely disappear, therefore it is important that the elimination diet is nutritionally complete to prevent signs of deficiencies and ill-health. If your pet is showing gastrointestinal signs (diarrhoea) these usually improve within a few days. During this trial period it is essential that your pet is fed only the selected protein diet and does not get any snacks, tit-bits or supplements. Even tiny amounts of other foods can ruin this diagnostic procedure.

THE CHALLENGE
In order to determine which protein sources you pet is allergic to, your veterinary surgeon may recommend testing different protein sources once your pet's clinical signs have improved. Suspected food items are introducing to the diet in small quantities - one new food ingredient per week. If the itching or diarrhoea that were previously present re-occur, it is likely that you have discovered an offending food ingredient. If you do not wish to attempt the food challenge, and your pet is happy on the elimination diet, you may continue to feed it as long as it is a complete and balanced diet.

LOOKING AFTER PETS WITH FOOD ALLERGIES
If your pet has been diagnosed as having a food allergy, the most important aspect of treatment is to avoid the offending food ingredient. By replacing the old diet with a new one, you can make your pet happier and healthier. Your vet has special diets available that contain ingredients that your pet is unlikely to have eaten in his previous foods. These diets usually contain a single meat protein source and a single source of carbohydrate. Such special diets are complete and balanced with all the essential proteins, fats, vitamins and minerals necessary for your pet's needs.

CARE AND ATTENTION
There are several general guidelines that may be of assistance in helping to identify the source of the food allergy, and the following up with a suitable long-term diet.

· If your pet has been prescribed drugs, make sure that you administer them exactly as prescribed

· Ensure that a plentiful supply of clean, fresh water is available - other fluids, such as milk, should be excluded, at least for the duration of the elimination diet

· When feeding the elimination diet, absolutely no other foods should be given. You may need to confine cats to the home for the duration of the test period. You may also need to separate pets in the household during feeding times

· The elimination diet may need to be fed up to a 6 week period before all the allergic signs are resolved. Be patient!

- Watch your pet closely for remission or a decrease in severity of signs during the elimination diet period, and inform your veterinarian of improvements or reactions to specific foods.

Tim Mainland MA, VetMB, MRCVS
www.vetontheweb.com

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