Food allergy is the third most
common cause of allergic itching and scratching in dogs. It occurs in dogs of
all ages. Unlike canine atopy, food allergy is not seasonal. Dogs can develop allergies to
chicken, milk, eggs, fish, beef, pork, horse meat, grains, potatoes, soy
products, or dietary additives. A dog must have been exposed to the allergen
one or more times to become allergic. Typically, the dog has been on the same
diet for at least two years.
The principal sign is severe itching, sometimesaccompanied by the appearance
of small red bumps, pustules, and raised patches of skin. Characteristically, the rash involves the ears,
feet, backs of the legs, and underside of the body.
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Since food allergy is less common than canine atopy and flea allergy dermatitis, the dog is often thought to be
suffering from one of those diseases. Many dogs will start by showing signs
just in their ears, with a red, moist rash.
Treatment: The diagnosis is made by placing the dog on a hypoallergenic test
diet and watching for a definite reduction in itching and scratching. A
hypoallergenic diet is one that has a very limited number of ingredients. It
should contain no added coloring, preservatives, or flavorings. Most important,
it should contain ingredients that the dog is unlikely to have encountered in
the past. Your veterinarian can prescribe an appropriate hypoallergenic diet
after carefully reviewing the composition of the dog’s current diet. Switching
from one commercial food to another is not an adequate test, as these
nonprescription diets contain too many ingredients and the dog is likely to
have eaten some of them in the past.
The test diet usually consists of a commercial hypoallergenic prescription
diet such as salmon and rice or duck and potato, available through Hill’s Pet
Products, Purina, and Waltham. Once a good commercial hypoallergenic diet is
found, the dog can be left on that diet indefinitely. Eliminate all treats and chews, and switch from a chewable tablet heartworm preventive to one that comes in a different
A reduction in itching may occur within a few days of starting the test
diet, but in many cases it takes several weeks. The test diet should be
continued for at least 10 weeks. Once improvement is noted, various foods can
be added one by one until the offending allergen is identified by noting that
it causes an increase in the amount of itching and scratching.
Purina has tried a new way to attack food allergies. Instead of simply
substituting novel proteins, their HA Hypoallergenic Diet uses modified and
denatured proteins of small molecular weight to render them nonallergenic. If
protein is the culprit, this kind of diet can be effective in controlling the
WebMD Veterinary Reference from "Dog Owner's Home Veterinary Handbook"