By Dr. Leslie Ross D.V.M, B.Sc.
Food allergies in pets are more common than most people think. In fact, about one in ten of all allergies seen in cats and dogs can be attributed to food allergies.
Signs of food allergies can occur at any age in a pet’ s life, with the first signs often starting before the pet is one year of age. In most cases the offending food substance was fed for quite a substantial period prior to when symptoms begin.
It has been my experience that the owners of pets that have been receiving a single type of food for long periods of time are often the hardest to convince that a food allergy may be involved when their cat or dog is experiencing skin or digestive problems. Quite understandably, the commonest two responses that I receive from clients when I bring up this subject during my examination of their dog or cat are either incredulous statements along the lines of: What! But I have been feeding Sheba (insert pet food type here) for years! How can it be possible that she has only now become allergic to beef? The second most common reaction is for clients to attempt to dispel my suggestion of a potential food allergy by earnestly describing their choice of pet food, which generally does seem to be a very good quality food. In general, both of these reactions are very understandable. In fact, I have come expect these responses and am always prepared to explain that food allergies in general are associated with a priming (sensitizing) process of the pet’s immune system and as such, take time to develop. In response to the second reaction, I try to make it clear that a food allergy is not to be correlated with a poor quality diet, but a diet with ingredients that may not sit well with an individual pet.
In people, the most common foods that cause allergic reactions are shellfish, nuts, eggs, milk, tomatoes and strawberries. In dogs the most common foods causing hypersensitivity reactions are beef, dairy, wheat, egg and chicken. In cats the most common food allergens are to beef, dairy, and fish. About 50% of food allergic animals are allergic to more than one food item.
There is definitely a genetic aspect associated with food allergies. Although any breed or cross-breed can be affected, certain breeds such as Boxers, Cocker spaniels, German shepherds, Shar peis, Westies and Wheaten terriers are over-represented from the general dog population for the development of food allergies. Current studies seems to indicate that inherited abnormalities in normal digestive system defense mechanisms predispose certain pets to food allergies.
At this point in my discussion, I would like to clarify the difference between food allergies and food intolerances. Although similar in some ways, food intolerances are caused by different mechanisms and, unlike food allergies, do not involve the immune system. Milk sugar intolerance in some cats and wheat gluten sensitivities in people are two good examples of food intolerances. Food intolerances are typically associated with an inherited enzyme deficiency that is usually apparent at birth.
Flea-free cats and dogs that are often itchy, no matter what the season, often have underlying food allergies. In fact, up to 57% of cases of itching and scratching in cats can be attributed to food allergies. More often than not, the itching and subsequent self- scratching involves the face and ears of cats. In dogs, their itching is often more non-specific in location and can involve their faces, ears, paws and rears. Keeping this in mind, behaviors such as head-shaking, ear-rubbing along carpets, foot-licking, and scooting all suggest some variety of allergy, including a food allergy, and warrant pursuit of this possibility as the underlying cause. In both cats and dogs, secondary skin and ear infections can often result from their constant scratching and these will worsen their miserable state of itchiness. In other cases, digestive disturbances such as persistent diarrhea, vomiting, frequent bowel movements or excessive gas production are sometimes the most noticeable clinical signs associated with food allergies.
Diagnosis of food allergies in pets, unlike the case with people, cannot be accomplished by any kind of blood test that is currently available. So, for pets suspected of having a food allergy to a currently fed food, it makes much more sense and costs much less in the long run for owners to spend their money on a specially formulated trial diet that can be both diagnostic and potentially therapeutic rather than on rather valueless blood tests.
A noticeable response to a dietary trial followed by the return of clinical signs when the offending food source is reintroduced remains the most effective method for diagnosis and management of pets with suspected food allergies or intolerances. In simpler terms, if the itch goes away during the hypoallergenic food feeding trial, and if systematically single foods are re-introduced one by one, then a list of foods to avoid can be compiled. Eventually, one can usually get the pet back on a commercial diet that fills the necessary requirements. The commonest duration of the food trial recommended by most skin specialists is a minimum of two months. I like to emphasize this point to pet-owners since sufficient time is necessary to properly interpret the benefit of the trial, especially for those pets with a well-established ear or skin disease. I also like to have owners remember to start counting this time interval past the duration of time when any medications are being administered to avoid benefit being attributed to the food when in fact it is due to the medication. Also of great importance is to be sure that all other snack foods, treats, table scraps, rawhides, milk bones, pill pockets, flavor enhancers, joint supplements and fish oils are avoided during this treatment period. Rawhide bones, nylon toys and pig’s ears also must be avoided. Dogs that live with cats must also be denied access to kitty litter boxes and the cat’s food. For variety, since most owners tend to feel badly about so much restriction of rewards, it is quite acceptable to offer the pet fresh or frozen green beans, carrots, slices of baked potato, baked tater tots, baked slices of the hypoallergenic canned food, or specially formulated hypoallergenic treats
Now, let’s discuss the trial diet itself.
The ideal trial diet should contain a limited number of novel, highly digestible proteins or specially processed proteins, and at the same time be nutritionally adequate for the pet. Most veterinary clinics have in stock, or can order in a variety of specially formulated hypoallergenic diets. Making the choice of a novel protein food can be a little tricky. Your veterinarian can help you with this. It is important to obtain a thorough history on the main protein source of previously fed foods to select an appropriate exclusion diet. A variety of rather unusual protein sources are available to choose from, including duck, venison, and rabbit to mention a few. (A rabbit and pea formulation is a good choice for cats in my experience, although not all cats enjoy its taste.)
If a suspected food allergic pet doesn’t enjoy any of the flavors from these specially formulated diets then homemade diets can be acceptable as initial test diets. However, if this option is chosen, it is important to consult with a veterinary nutritionist to ensure that the diet is complete and balanced, even more so if this is planned as a long-term maintenance diet. An online website, (http://www. balanceit.com,) is a good source of information regarding homemade diet analysis for those folks wishing to pursue this approach. Even vegetarian diets can be considered for food allergy trials for dogs, but only if the dog is not allergic to vegetable proteins!
The selection of novel protein sources commercially is becoming more narrowed all the time because what used to be a rare protein source such as fish, duck or venison is now much more commonly available, either as single sources or sometimes even in various combinations.
It is important to be aware that, unfortunately, not all commercially available limited or novel protein diets are created equal. In fact, it was presented at a fairly recent North American Dermatology Forum that a study showed a large amount of cross contamination of proteins in many of the available over-the counter novel protein diets. This is believed to be because multiple diets are produced on the same line in most of these plants. Pet food companies are also allowed to change ingredients without changing the label under the six-month substitution rule. So, if an ingredient is temporarily unavailable they can use something else without mentioning it on the label. Of course, even if an ingredient isn’t listed on the label, a company with lax standards or quality control may end up including trace amounts of foreign protein into their “novel protein” or hypoallergenic diet.
So, what is one has to do when trying to decide on an over-the-counter diet for food- allergic animals really amounts to trial-and-error.
As I approach the conclusion of this subject, I feel it is worth mentioning that ongoing validity studies are being conducted on a saliva test developed by Dr Jean Dodds at Hemopet to identify food sensitivity and food intolerance in dogs. Unfortunately, so far at least, the general consensus by researchers is that continued investigation and refinement of the test is necessary prior to practical use. Probiotics are also being studied to determine if alteration of the gut-flora of these pet-allergic pets may help with their gastrointestinal defense capabilities.
Ultimately, it sure would be a huge stride forward if we could find some way to more accurately identify the foods to be avoided in these food-sensitive pets rather than focus on those food substances less likely to be reactive to them.