Food allergy is one of the itchiest conditions for cats and dogs and one which we see frequently at the Manchester Animal Hospital. Animals eat a variety of processed food proteins, flavorings, and colorings that 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, the skin is frequently included in this immunologic activity.
Cats itch around the face or neck, which produces scabs and hair loss. In dogs, signs include facial itching, foot or limb chewing, itchy anal area, and recurrent ear infections.
Many people erroneously assume itching due to food allergy requires a recent diet change of some sort. In fact, the opposite is true. Food allergies require time to develop; most animals have been eating the offending food for years with no trouble. The resultant symptoms require trying to determine what Kind of Allergy it may be.
Diagnosing and treating allergic skin disease and its secondary infections make up a large proportion of cases seen in small animal practice. Pets can be allergic to insect bites, however 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.
Th following are some clues:
Any of the above findings or observations warrant the pursuit of food allergy.
To determine whether or not a food allergy or intolerance is causing the skin problem, a hypoallergenic diet is fed for a set period. If the pet recovers, the original diet is fed for up to two weeks to see if itching resumes. The test diet is determined by a blood serum test to determine which proteins the pet may be allergic to.
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.
Before reviewing diet strategies for this process, here are some additional concerns:
Diet trials often span a season change period. If a dog has a pollen allergy and winter comes during the period of the diet trial, it may appear that the diet worked when, in fact, the seasons simply changed. This is why a diet challenge is important at the end, even if the pet is doing well.
The diet trial will take eight weeks. Most animals will respond in three to four weeks, but to be sure, you will need to feed the test diet for two months.
There are two approaches to test diets: novel protein and hydrolyzed protein. Traditionally, a novel protein is used. This is a diet with a single protein source that the patient has never eaten before. It typically takes years to become allergic to a food protein so the patient should not be allergic to something new.
Fortunately, many pet food companies have discerned the need for diets using unusual protein and 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 allergy trials must contain one protein and one carbohydrate source, and neither can be something the pet has had before. Recently, several diets that include duck, venison, and so on 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 are ever used in the pet’s regular food.
Recently several pet food companies have released single protein diets for over-the-counter sales. These tend to cost less than the therapeutic diets available from your veterinarian’s office directly. While these diets are attractive, they are probably not a good choice for an actual diet trial. Immunological tests on these foods found that many of them contain additional proteins (probable contaminants from prior batches in the pet food factory). These impurities could defeat a diet trial which is hard enough to perform without such issues. The therapeutic diets did not have these contaminants.
Home cooking is a fine alternative to commercially prepared foods for the diet trial. The problem is that the test diets will most likely not be balanced but for the two months or so of testing, this should not be a problem. Home cooking is a bit of an inconvenience, but for the right person, it is a good choice. Ideally, a nutritionist should be involved in designing the diet. Recipes for appropriate diets can be recommended by any nutritionist listed at the American College of Veterinary Nutrition website.
Several therapeutic diets are 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 various hydrolyzed diets on the market; discuss with your veterinarian which is best for your pet.
Studies have shown that 80 percent of dogs will have shown a response by four to six weeks on the diet, but by extending the diet to eight weeks, 90 percent will respond. The Labrador retriever and cocker spaniel appear to require longer trials. Most veterinary dermatologists recommend eight to twelve weeks, which is a long time to be strict on the diet, but that is the only way to detect food allergic dogs.
To confirm food allergy, return to the original food; itching generally resumes within 14 days 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 to 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.
Assuming secondary skin infections have been controlled, an unsuccessful food trial is strongly suggestive that an inhalant allergy is a primary problem, but some other considerations 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 that pointed 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, hypoallergnic injections, symptomatic relief either via medication, baths with specific shampoos, or allergy shots will likely be necessary.
Chronic itchiness can be extremely uncomfortable and prompt relief is an essential goal.
Dr. Lamb is the Veterinarian at the Manchester Animal Hospital.
