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. Dog 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, sometimes accompanied 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.
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 nonpre- scription 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 form.
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 allergy.