Food Allergies and Intolerances

Pets can have dietary sensitivities such as food allergies and intolerances, just like people. It is estimated that 10-20% of the pet population suffer from adverse food reactions of some type. Although allergies and intolerances can show up in many forms, they often present as skin disease or gastrointestinal (GI) upset. GI signs can range from mild bloating and flatulence to severe diarrhoea and vomiting. Signs of skin disease can also be variable ranging from itching to rashes to hair loss or even ear disease.

Food allergies are caused by the animal’s body mistakenly mounting an immune response to certain ingredients in the diet, causing inflammation in certain parts of the body, usually either the gut or skin. These occur when the animal’s body reacts to a glycoprotein contained in food – a protein linked to a carbohydrate. Generally, the protein component is the culprit, but occasionally, the carbohydrate can be responsible. The most common food ingredients responsible for food allergies in dogs are: beef, milk, chicken, lamb, wheat, soy, corn, egg, pork, fish and rice (in descending order).

There appears to be a higher allergenicity in processed foods versus fresh foods, potentially due to the changes in the structure of the food molecules which occurs with cooking. Food allergies tend to initially manifest in younger animals, typically between 1 and 4 years of age. There does not have to be any dietary change for an allergy to occur – an animal may have been (and usually is) fed the same diet for some time and has tolerated it well, then ‘suddenly’ develops the allergy.  Dogs may be allergic to more than one ingredient. In fact, those that have one allergy are more likely to develop further allergies over time.

Food intolerances are due to the animal’s body not being able to properly ‘process’ an ingredient, or a toxic reaction to it, rather than an immune reaction; GI signs are more commonly seen with this type of food sensitivity than skin signs. In dogs, a range of ingredients including proteins, some grains, soy and dairy have been implicated in food intolerances. Some breeds appear to be more sensitive to intolerances; for example, some Red Setters have a genetic sensitivity to gluten which can cause poor digestion, poor health and weight loss.

Food intolerances tend to resolve far more quickly than food allergies when the offending food is removed from the diet – often within days, whereas food allergies can take weeks to resolve. With food allergies, those which involve skin signs tend to be much slower to respond to a dietary change than those which involve GI signs.

itchy dog

But, clinical signs of GI upset or skin disease are not specific for a dietary cause and several other diseases can present with exactly the same signs. For example, itchy skin could be due to parasites and/or an allergy to them, either environmental or contact allergies, or other internal diseases such as hormonal problems. Diarrhoea may be due to parasites, bacteria or other internal diseases such as pancreatitis or hepatitis. Several steps and tests are usually needed to work out exactly what is causing the problem.

For this reason, suspected adverse food reactions are best diagnosed by a vet, who will likely advise a proper diagnostic work-up to rule in or out all the potential diseases, including a food elimination trial where novel foods (foods that the dog has never eaten before) are fed exclusively for a period of weeks; often a ‘single source’ protein diet to see if the signs resolve. The previous diet is reintroduced and the dog is assessed to see if the clinical signs recur.

Once an allergy/intolerance has been identified, the dog should be maintained on a diet that does not contain the ingredients that they are sensitive to. These dogs are best fed diets where the specific types of animal protein can be identified so that the offending ingredients can be avoided. Ingredients listed as ‘meat’ or ‘meat meal’ that do not specify which animal they were sourced from should be avoided as they are likely to include meat from several different animal sources.

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