Overview of Canine Food Allergy
Food allergy is an uncommon problem in dogs and it can start at any age. A change in diet is not necessary for development of food allergy. About 70 percent of affected pets develop allergies to food ingredients that they have been fed for a long time, usually more than two years. In fact, if your dog has an immediate adverse reaction to a new food, it is probably not an allergic reaction, because it takes more than one exposure to produce an allergic reaction.
Food ingredients most commonly responsible for allergies are beef, chicken, fish, eggs and milk. The tendency to develop allergies is genetically determined. Dogs with other allergies like inhalant allergies or atopy may be at increased risk for developing a food allergy.
The clinical symptoms of food allergy resemble those of other types of allergies. These two disorders may have the same clinical symptoms and the same distribution of itchiness or pruritus over the dog’s body. In some cases, it is impossible to differentiate between inhalant allergy and food allergy by clinical appearance alone.
Food allergy should be ruled out first because it is the easier of the two disorders to control by eliminating the offending food ingredient from the dog’s diet. Food allergy is ruled out by feeding a diet consisting solely of food ingredients to which the animal has not been previously exposed – an elimination food trial. This trial should be performed before considering expensive tests for other types of allergies.
What to Watch For
Diagnosis of Food Allergies in Dogs
Diagnostic tests are needed to recognize food allergy and exclude other diseases that may cause similar symptoms. Tests may include:
Treatment of Food Allergies in Dogs
Treatment for food allergy may include one or more of the following:
New food allergies can develop over time. If your dog was diagnosed previously with food allergy and has been well controlled with a special diet but once again is showing signs of allergic skin disease, he may have developed a new allergy. Under these circumstances, consult your veterinarian to determine whether a new allergy has developed or whether another disease is present.
Another elimination food trial may be necessary to make this distinction. Patience and determination are important for the success of an elimination food trial. You and your family must be strict and be certain that no one “breaks” the food trial by giving the dog treats or table scraps. Strict compliance with the trial is essential for proper interpretation of the results. This means no treats like milk bones, rawhide bones or pig ears, no flavored medications (Heartgard Plus), and no flavored vitamins during the trial.
A genetic predisposition seems to exist for food allergy. Based on their genetic constitution, some animals seem to be predisposed to development of food allergy. However, since the cause of food allergy is unknown, the disorder cannot be prevented.
In-depth Information on Food Allergies in Dogs
The term food allergy often is used to describe any adverse reaction to foods. Some reactions are mediated by the immune system (true allergy) whereas others are not (food intolerance). Food intolerance and true allergy cannot be reliably differentiated on a clinical basis, and this difficulty explains why a variety of clinical signs are attributed to what has broadly been called food allergy.
Barriers in the gastrointestinal tract prevent adverse responses to ingested food in most individuals. These barriers include both physiologic and immunologic protective mechanisms. Abnormalities in the gastrointestinal defense mechanisms (mucosal barrier failure with increased antigen absorption, defective immunoregulation) may predispose your dog to the development of food allergies. Which of these mechanisms is important in the pathogenesis of food allergies in dogs presently is unknown.
The pathogenesis of food allergy in dogs has not been established. Type I hypersensitivity (mediated by a type of antibody called immunoglobulin E or IgE) may be involved. In this type of hypersensitivity reaction, mast cells in the intestinal tract degranulate and release inflammatory mediators.
Foods contain many proteins that can act as allergens. Allergenic foods tend to have high protein content. Complex proteins contain many sites that may act as antigens and thus are more likely to stimulate the immune system than are smaller proteins. Offending proteins must be large enough to link two IgE antibodies and trigger mast cell degranulation.
The foods most commonly incriminated as allergens in dogs are beef, dairy products and wheat and account for 66 percent of suspected cases of food allergy. Chicken, lamb, soy, eggs, pork, and preservatives account for only 22 percent of reported cases according to a recent survey of veterinarians in North America.
Reactions to food additives frequently are suspected, but little objective information supports this perception. Additional studies are needed to confirm the role of food additives in adverse reactions in dogs.