What are the clinical signs of food sensitivities?
The most common signs of adverse food reactions involve the digestive system. These are present in about ⅔ of dogs which suffer from food reactions. These signs may include vomiting, diarrhoea, flatulence, a “rumbly tummy”, bloating, an increased frequency of defaecation or straining to pass stools. There is a syndrome in dogs known as “food-responsive enteropathy” which is responsible for 40-60% of cases of chronic diarrhoea in dogs. In these animals, a change of diet to a novel protein leads to resolution of the clinical signs. The food sensitivity wanes over time in such cases, and after around 6 months of dietary exclusion, they are able to tolerate the previous diet again. These dogs do not have a food allergy, but rather a food intolerance.
Adverse food reactions (including both allergies and intolerances) in dogs have been estimated to be responsible for 10-20% of all allergic skin diseases. However, it is suspected that due to the complicated way these are diagnosed (see diagnosing food allergies or intolerance: food elimination trials article), many cases are misdiagnosed, or simply not diagnosed at all, so the true prevalence in pets is unknown.
The most common skin sign noted in dogs suffering from food reactions is itching. The itching can be all over the body or limited to certain areas, such as the face, feet, ‘armpits’ or around the bottom. The skin is inflamed and tends to be red with lumps and bumps on it. Itchy, infected ears are also common, and may be the only sign in about a quarter of dogs – and in some cases, only one ear may be affected! Because of the itchiness, dogs scratch and bite themselves, which damages the skin, causing scratches, grazes and scabs. Due to the broken skin, secondary infections with bacteria or yeast are common, which can be smelly or ooze pus and usually require medication to resolve. And because dogs pull hair out during scratching and biting, bald patches are often noted.
The itch tends to persist throughout the year once it starts (unlike other types of allergies which tend to be quite seasonal). These are usually not triggered by a change in diet and often occur suddenly after months or years of consuming the same diet.
Rarely, other signs such as a lack of energy or seizures may occur as the result of an adverse food reaction. But none of the signs are specific for a food reaction and can overlap with many other diseases. In fact, many dogs which suffer from food reactions suffer from other diseases as well, especially allergic diseases, such as flea allergy dermatitis.
Both males and females tend to be equally affected by food reactions. The age of onset is variable: anywhere from 2 months to 14 years of age, but up to 4 years is typical, with about half of the dogs being less than one year of age when the disease first presents. Some breeds, such as Labradors, German Shepherds, West Highland White terriers and Spaniels are more commonly affected, but any breed or cross-breed can be affected.
Adverse food reactions cannot be cured, so a full food elimination trial including rechallenge should be carried out to determine what the dog is reacting to, and that ingredient or food should be avoided in the long-term diet in order to manage the clinical signs.