Food Allergy in the Dog and Cat

by Christopher Forsythe, DVM

It is often said you are what you eat, and this is also true for our four legged friends. Unfortunately the itchy problem of food allergies can make a pet and his guardian alike go bonkers, the pet scratching for relief and the owner going loopy searching through bags of food looking for a magic cure. In this issue I will address food allergy, an immune reaction to food that is seen in both dogs and cats.

Diet has long been recognized as a cause of hypersensitivity-like skin reactions in dogs and cats. Allergy to food is the third most common hypersensitivity skin disease after flea bites and atopy (inhalant allergy). There are many breeds of dogs that may be at higher risk for development of food allergies. Labrador Retrievers, Cocker Spaniels, Springer Spaniels, Miniature Schnauzers, Lhasa Apsas, Soft-Coated Wheaten Terriers, Dalmatians, Boxers, and Shar-Peis are all over represented compared to other breeds. Studies show that males and females have the same rate of food allergies, and age at presentation can vary from young to old.

History and Clinical Signs

Almost every pet who has a food allergy itches and scratches like a girl at a slumber party whose brother has put itching power in her sleeping bag. The itching is relentless, and the pet will scratch and chew himself raw. Often scratching is directed at their own feet or ears. Common secondary sores include red rings called “collarettes” as well as traumatic red areas called “hot spots.” In cats, food allergy often presents as itching around the head and face.

Other diseases that cause similar clinical signs in dogs and cats include atopic dermatitis, or allergy to weeds, grasses, trees, pollen, and household allergens such as dust and dander. Flea bite dermatitis is another cause of severe allergy in dogs and cats that presents like food allergies. These very common and nasty symptoms occur after a flea bites a pet thus inoculating with a tiny amount of flea saliva while taking a blood meal from your pet. Days to weeks later many pooches will suffer delayed hypersensitivity reactions and break out with sores and rashes which make them look worse than a Tenderloin crack user. Many pets with food allergies have a concurrent component of one or more of these, so we should address the symptoms and also diagnose the underlying disease as well. Antibiotics, steroids, baths, and dips can help treat secondary infections, but the true diagnosis of a food allergy is still an “elimination” diet.

Elementary, my dear Watson

According to most veterinary doctors, including specialists and referral dermatologists, the ideal way to diagnose a food allergy is to feed a hydrolyzed protein or hypoallergenic diet. This diet employs a protein source that is hydrolyzed to small molecular weights thus avoiding the body’s immunologic recognition system. Why does this make the diet special to your pet? It is generally believed that the protein source in a diet is the molecule responsible for your pet’s system’s reaction. This reaction is what causes a negative immune response and subsequent itching and sores. Purina’s HA and LA and Hill’s ZD diets are made with a process that cleaves the proteins so they are too small to be noticed by the pet’s immune system. Since the pet’s immune system cannot recognize them as irritating or foreign, the allergic process slows down or stops.

The elimination diet generally contains one protein and one starch based on the dog’s previous exposure to various food stuffs. Dogs who live in households with cats have likely been exposed to fish since they most likely occasionally sneak a snack from the kitty bowl or kitty litter. Some commercially available elimination diets include Purina LA (Salmon), Iams (Fish and Potato) and KO (Kangaroo and Oats). These novel sources of proteins represent a fresh start for the pet and allow the immune system to take a break from the barrage of irritating proteins.

Tough love. It’s like boot camp!

Ah yes, but the rewards can be bountiful. Better skin in just eight weeks. Without creams or gimmicks! In my practice I let clients know their pet needs to eat the prescribed food only, without as much as a speck of anything else for a minimum of eight weeks. This means tough love. No scraps, none of their previous food, milk bones, or anything except the prescribed diet. Owners need to agree to this because just a small amount of a hot dog or other morsel can set the pet back to square one. Owners with small kids in high chairs, for example, need to watch for falling food so to scoop it up before the family pet sharks it down.

Clinical signs in the waylaid pooch often begin to improve in as early as seven days, and if vast improvements are notable and obvious, in the absence of other remedies (such as antibiotics, baths, dips), your pet should now be challenged with her regular diet to confirm the food allergy diagnosis. This means you feed Fido his old food to see if his old clinical signs return. I know this may seem mean but it is the only way to truly confirm the problem at hand. Recurrence of clinical signs usually begins within one week but may take as long as two weeks. At that point the pet is given the elimination diet again, and the pet owner may then elect to challenge with suspected allergens, each one being given one to two weeks at a time. The most common allergens are beef, chicken, milk, eggs, corn wheat, and soy. In cats, fish and milk products usually are the offenders. Allergies to more then two allergens are uncommon. Once the offending allergens are identified, you may feed your dog commercially prepared dog foods that do not contain those specific allergens.

Serology: blood testing to help detect food allergy

Over the past few years, veterinarians have begun utilizing blood testing to determine which foods pets are the most allergic to. The test measures your dog’s levels of Immunuglobin E (IgE) produced in response to various food proteins, and this information is quantified. Experts suspect that those foods that cause the highest numbers are probably the most allergenic and you should avoid or eliminate them altogether. According to Dr Bernadette Bylina, DVM of HESKA Corporation, “We know serum allergy testing for IgE in humans for food allergy may be commonly pursued. We don’t know yet what those applications are yet for veterinary medicine.”

It is widely thought by veterinarians that allergies of all types, including those to food, are among the most difficult diseases to accurately diagnose and treat. Because there are many variables and requirements for success the stars and planets seem to have to line up precisely with success is measured over weeks and months, not days. With this information, you and your veterinarian can hopefully make your pet more comfortable and less itchy, even though it may take a little time and patience, especially by your dog, to succeed.