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Food Allergies in Dogs

Food Allergies in Dogs

Food Allergies in Dogs

By Elizabeth Pask and Laura Scott
Courtesy of Modern Dog Magazine

Is your dog itching and scratching? Does she have frequent ear infections or poor coat quality? You could be contributing to your dog’s distress without knowing it if she’s allergic to what you’re feeding her. Food allergies are a rising concern with dog owners and it seems like more and more dogs are suffering from them.

But what exactly is a food allergy?
Food allergies are different from food intolerance. Food intolerance is the result of poor digestion, such as lactose intolerance. People and dogs with lactose intolerance are either missing or have low levels of the milk digesting enzyme lactase.

Food allergies are the over-response of your dog’s immune system to an invading protein. In the case of a food allergy, this protein is contained in your dog’s food. Proteins are present in most of the foods your dog eats. While most people recognize that meats are a source of proteins, there are also proteins present in grains and vegetables. Any one of these proteins has the potential to cause a food allergy.

Your dog’s gastrointestinal system (mouth, stomach, intestines) protects her from potential allergens each day. Approximately 70 percent of the body’s entire immune system is centered in the gastrointestinal tract. When your dog eats a meal, the food is first digested in the stomach. The large pieces of food are broken down into smaller pieces by stomach acid and then enzymes and stomach acid work together to break the complex protein structures down into smaller structures. The partially digested food then moves into the small intestine. The food is further digested until the proteins are broken down into their smallest parts, amino acids, which can then be absorbed into the body through special cells called enterocytes. Enterocytes act as both a welcoming hostess to amino acids that they like and want, and as bouncers (door guards) for amino acids they don’t like. When a whole protein is absorbed in the intestines instead of being broken down first, the immune system reacts and your dog shows symptoms of a food allergy.

When the System Works
The intestinal tract’s ability to prevent the absorption of whole protein is dependant on the health and integrity of the mucosal barrier. It is the proverbial guardian of the body at the gastrointestinal gate. The mucosal barrier (lining of the gut) is comprised of both structural components and immune system components. The structural components physically prevent the absorption of large proteins. The immune system component is responsible for recognizing potentially harmful contents of the gastrointestinal tract. The health and integrity of the gastrointestinal tract is dependant on the normal structure and function of the enterocytes, effective protein digestion, and the presence of the dog’s immune cells (called IgA cells) in the gastrointestinal tract.

The Gut and Immune System Together Prevent Food Allergies
IgA cells are a type of immune cell secreted in the intestine. Some of the IgA will float freely in the contents of the intestine while other IgA attaches to the wall of the intestine to prevent whole protein from coming in contact with the enterocytes. Just like volleyball players they bounce whole proteins back into the contents of the intestine for more digestion. The more effective protein digestion in the stomach and intestine is, the smaller the proteins are when they come in contact with the IgA. Small proteins and single amino acids do not get bound to the IgA and are allowed to pass by the IgA and be absorbed into the body as nutrients.

When the System Fails

Malnutrition can affect enterocyte structure and function. A poorly functioning or damaged enterocyte can let whole proteins into the body. Once a whole protein has managed to breach all of the gut’s defenses, gut-associated lymphoid tissue (GALT) takes over. GALT can prevent the body’s natural immune response to a foreign protein. Most of the time this is what happens, but in the case of food allergies, GALT does not prevent the immune response and an allergic response (immune hypersensitivity) is formed.

Unfortunately, every time the food is eaten, this over-response of the immune response becomes greater. So continuing to consume the diet that caused the allergic response results in a greater and greater response every time. After this hypersensitivity is formed, each time the dog eats the food, mast cells in the body’s immune system release hertamine. If this hertamine release is large enough, it may manifest as diarrhea, itchy skin, chronic skin infections etc.

Click here to read more about Food Allergies in Dogs: Modern Dog Magazine


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