Food adverse reactions may be immunologic (food allergies – hypersensitivity reaction) or nonimmunologic (e.g. food intolerance, toxic food reactions).
They can induce cutaneous and/or gastrointestinal clinical signs (vomit and diarrhea).
Food intolerance is an organic response that can be caused by proteins, food additives, toxins or bacterial contamination.
It is the most common adverse reaction to food in dogs.
Food allergy accounts for approximately 31% of non-seasonal dog dermatitis cases.
It is a common cause of cutaneous and chronic gastrointestinal signs.
It results from an immunological reaction to specific glycoprotein molecules produced during digestion.
Clinical signs occur in dogs as young as four months, up to 12 years of age.
However, 50% of food-allergic dogs are younger than one year of age when diagnosed.
Generalized pruritus is the more frequent feature of food allergies, in some cases with a preference for the feet and inguinal area.
Here are other symptoms of dog food allergies:
- recurrent bilateral otitis externa
- hot spots
- face rubbing, hair loss
What is a food allergen?
Food allergens are almost exclusively protein molecules.
All dietary proteins have the potential to induce an allergic reaction because they are recognized as foreign by the immune system.
The size and structure of dietary proteins influence their ability to induce a hypersensitivity.
Frequent food allergens are proteins with molecular weight of 18,000 to 36,000 daltons.
The most common allergens recognized in spontaneously food allergic dogs may diverge according to geographical location.
Some examples of protein sources that commonly induce food allergies are:
- dairy products
Pathophysiology of Food Allergies
The pathogenesis of food allergies is intricate.
It embraces the following mechanisms:
- permeable intestinal mucosal barrier
- atypical antigen presentation to the immune system
- deregulation of the immune system
- loss of oral tolerance
A dog’s gastrointestinal tract is exposed to considerable amount of potential allergens.
But a small percentage of the canine population presents food allergies.
So, the gastrointestinal system has evolved to provide defense mechanisms against to potential harmful immune responses to food.
Digestion of protein represents the most effective preventive process.
In the gastrointestinal system the majority of food allergens are inactivated during the digestive process.
Nevertheless, some food proteins persist immunologically active and gain access to the circulatory system.
For food allergy to develop, food allergens must rupture the intestinal barrier in order to be visible to the local immune system (GALT).
Allergic sensitization to ingested food allergens occurs in the GALT, where allergen-specific IgE fixes to high affinity IgE receptors on the surface of other immunologic cells (mast cells and basophils).
Succeeding exposure to the same food, cross-linking of antibody-primed IgE receptors leads to mast cell degranulation, discharge of inflammatory mediators and beginning of clinical symptoms.