Food Allergy In Dogs

The true incidence of food allergy is unknown. Approximately 23% of all dogs with allergic skin disease are actually allergic to some ingredient in their diet. About one-fourth of these dogs are also allergic to substances other than foods as well, such as fleas, ragweed, etc.

Dogs with food allergies can start showing clinical signs at any time of the year, and it is usually a constant problem. However, food allergy can be episodic when the dog eats the offending food only periodically, such as a particular type of treat or rawhide chew.

Food allergic dogs usually itch and scratch, sometimes in combination with diarrhea. Unfortunately, many problems cause itchy skin (such as fleas), so sometimes a diagnosis of food allergy is overlooked. Most dogs will itch all over, but some will tend to chew on just one foot, or will just scratch their ears. Steroids prescribed by your veterinarian to control itching do not work very well in the dog with food allergies.

Typically, signs of itchy skin will appear within several hours after eating the offending food. Dogs fed in the early morning may tend to scratch more in the afternoon or early evening. Dogs fed in the early evening may keep the house awake at night with their constant scratching. Food allergy may occur at any age, but most cases occur after the dog has been exposed to the particular food for two or more years. It is not uncommon for a dog to suddenly become allergic to the food it has been eating routinely for several years.

Almost any dog food ingredient can cause an allergic response. The most common allergen is the protein source in the diet, which may include beef, milk, chicken, lamb, egg, pork, horsemeat, rabbit or fish. Wheat, corn, rice, flour, potatoes, soybeans and kidney beans may also cause signs of food allergy.

The gastrointestinal tract of the dog is essentially a large tube lined with cells that control the absorption of nutrients from food. These cells also protect the body against injury from a number of harmful substances. Certain immune cells (B lymphocyte cells) produce antibodies such as IgG and IgE. These immunoglobulins protect against invasion by bacteria and parasites, and control the absorption of antigens which can stimulate antibody production.

In the normal dog, the ingestion of a particular food causes a very small amount of IgE to be released. This small amount of IgE is quickly controlled by other cells of the immune system. However, in the allergic dog, a much larger amount of IgE is produced in response to a particular food. The immune system cannot control this large amount of IgE produced, and clinical signs of food allergy result. The amount of IgE produced depends on a number of factors, including the genetic predisposition to allergy, and the length of time the dog has been exposed to the offending food. It is not uncommon for a dog to become suddenly allergic to a food it has eaten for years. The large quantity of IgE produced stimulates the breakdown of mast cells which are present in the skin and gut. These mast cells release a number of irritating substances that cause itchy skin and diarrhea.

First, all other causes of itchy skin should be ruled out. Take your dog to your veterinarian to make sure that your dog does not have a bacterial or fungal skin infection. Pay special attention to flea control, since allergies to fleas are a common cause of itchy skin. Once other causes of itchy skin are ruled out, a change in diet is probably warranted.

Many diets currently on the market claim to be hypoallergenic. These diets do not actually prevent allergies, but usually represent a novel source of protein. Realize that your dog may be allergic to any ingredient, typically the protein source. The first step is to take a look at the ingredient panel of the dog food you are currently feeding. If the protein source of your current food is poultry, then a switch to a lamb-based dog food is a good choice, since your dog has not been exposed to this type of protein. The new food may have to be fed for 3 to 4 weeks for a noticeable improvement to be seen. If there has been no real improvement after a month on the new food, your dog may be allergic to one of the other ingredients in the food, and your veterinarian should be consulted for help in diagnosing the allergy.