Dermatologic manifestations and nutritional management of adverse food reactions - Veterinary Medicine
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Dermatologic manifestations and nutritional management of adverse food reactions
A properly conducted limited-antigen diet trial will help you determine whether a patient's dermatologic and possible concurrent gastrointestinal signs are due to food allergy. This dermatologist guides you and your clients through the process of performing such a trial, including how to overcome common complications.


Diet selection

Traditionally, the identification of adverse food reaction has relied on feeding a novel protein source (one to which the animal has had little or no previous exposure). This novel protein is usually combined with a carbohydrate and may be fed as a commercial or home-cooked diet. As the variety of protein sources available in over-the-counter commercial pet foods has expanded, the choice of novel protein sources has become more limited. This and other factors have led to the recent development of balanced hydrolyzed protein diets.

In many cases, a commercial diet is selected over a home-cooked diet, as owner compliance is often better with commercial products. Confirmed reports of animals tolerating home-cooked diets and not the commercial equivalent containing similar ingredients are rare (eight dogs and one cat).14-16 Home-cooked diets are often advocated to avoid pet food additives that might have the potential to cause adverse reactions. However, although additives are often incriminated as causing adverse reactions in pets, there are no well-documented reports to support this idea. Forty dogs with adverse food reaction confirmed after being fed home-cooked diets could not subsequently tolerate commercial novel protein diets. However, no attempt was made to identify the problem allergen in those cases.17 Home-cooked diets should not be used at all in growing dogs or in cats for more than four weeks without being nutritionally balanced by an experienced veterinary nutritionist. In these cases, skeletal or organ pathology can result from a poorly balanced diet.

Tips to enhance dietary acceptance by the pet
A number of commercial hydrolysate diets are available for both dogs and cats. In these diets, a common protein such as soy or chicken has been digested to produce smaller peptides. In theory, these peptides are too small to initiate an IgE-mediated reaction. The claim for efficacy in veterinary patients therefore assumes that most adverse food reactions in cats and dogs are IgE-mediated. Whether this is the case is currently unknown.

A further limitation to the use of hydrolyzed diets as test diets is the lack of data documenting whether dogs allergic to the parent protein can tolerate the hydrolyzed product. Nestlé Purina Veterinary Diets HA HypoAllergenic Canine Formula (Nestlé Purina) containing hydrolyzed soy protein and cornstarch has been evaluated in two small studies of dogs with pruritic skin conditions. A randomized blind feeding study demonstrated a reduction in pruritus in soy-and corn-allergic dogs fed this diet of 50% and 80%, respectively.18 When HA Formula was fed to the Maltese-beagle dogs at North Carolina State University, 11 of 14 dogs (78.6%) with soy or corn allergy or both showed no adverse effects.7

However, regardless of whether you select a novel protein, hydrolyzed, or home-cooked diet, your choice of diet should be based on a thorough dietary history that should include not only the main diet but any frequently fed treats or table scraps. This will allow selection of a truly novel protein source. Cost and palatability are also major considerations for many clients (see the boxed text "Tips to enhance dietary acceptance by the pet").

Client compliance

Lack of client compliance is generally the biggest reason for the failure of dietary trials. Often, poor compliance is due to inadequate client education by the attending veterinarian. In fact, one study showed that before improved client education was initiated, 52% of diet trials failed during follow-up, compared with a failure rate of 27% after better client education was instituted.9

Owners must understand that the diet should be fed exclusive of all other foodstuffs. Either the veterinarian or veterinary technician must schedule time with the owner to explain the premise of the test and reasonable expectations from the procedure. It is also useful to provide handouts that detail the protocol. A follow-up visit after two to four weeks will identify any problems or indiscretions and is often needed to encourage the owner to maintain the trial protocol.


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