Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

No substance we put into our bodies is ever 100% safe or healthy. Food is also not always “benign”. Eating too much of something, too little of something, the wrong kind of food for a life-stage or a clinical condition can all compromise a pet’s health.

I have classified health problems brought on by diet under four headings: Food intolerance, food allergies, toxins in the food, and a nutritionally mediated disease.

Reaction
Food allergies or food intolerance are caused by a reaction to a particular ingredient. Sometimes referred to as an “adverse reaction to food”, it is defined as an abnormal response to a food or food additive.

There are two classes of adverse reactions: Those in which the immune system is involved (generally called food allergies); and those that occur without an immune component (generally called food intolerances).

Food intolerance can be likened to gluten or lactose intolerance in people, where a specific ingredient is either not digested or irritates the GI and this causes gastrointestinal symptoms such as bloating, diarrhoea or bowel irritability. There is no direct immune reaction to the food components as foreign to the body.

Allergy
A food allergy occurs when the body reacts to an ingredient in the diet with an immune response. It may take months or years before your dog develops an allergic response to a particular food.

However, once he’s allergic, he will almost always have a negative reaction to that food. Allergic reactions are most commonly associated with protein sources (meat), but are also caused by milk products and wheat in your dog’s food.

The most common symptoms of a food allergy or intolerance are digestive upsets or skin irritation.

They are frequently characterized by itching and less commonly by gastrointestinal signs.

Skin lesions on dogs are frequently located on the face, feet and ears, but this is not specific to food allergies. Dogs with chronic or recurring external ear infections should be evaluated for food allergies.

Specific diagnosis of food allergies in your dog is difficult, but if your dog vomits frequently, has diarrhoea, irritated skin, a poor coat condition or hair loss, then he may have a food allergy.

Toxins
Toxins in the food can occur naturally or accidentally or maliciously. A common toxin occurs when mould grows in the grain part of the ingredients. The moulds can colonize and contaminate food before harvest or during storage, especially following prolonged exposure to a high-humidity environment, or to stressful conditions such as drought.

These moulds produce aflatoxins, which are very toxic to the liver. Reputable dog food companies will take samples from their raw ingredients and check for harmful levels of aflatoxins. In dogs, aflatoxin will likely cause liver disease.

Low levels of aflatoxin exposure require continuous consumption for several weeks to months in order for signs of liver dysfunction to appear. High-level aflatoxin exposure produces an acute liver damage resulting later in liver cirrhosis.

Toxins can also occur due to incorporated chemicals. The melamine, which was deliberately added to raw ingredients shipped from China to artificially increase the protein percentage of the ingredient, caused a worldwide food recall as it cause irreversible renal damage and failure and many pet deaths.

It was also present in some human products in China.

Dog food can also become contaminated with other animal feed additives such as growth stimulants (ionophores) in production animals, which is toxic to horses and dogs. This occurs when a large company uses the same production line to run different products for different species.

Mediated
In the case of nutritionally mediated disease there is nothing wrong with the food per se, but the food is not suited to certain individuals and will exacerbate or cause clinical disease in those pets.

We have known animal examples of this: Miniature Schnauzers get bladder stones and pancreatitis if on a diet high in minerals or high in fat respectively.

So, the problem is not the food but the combination of the food and a susceptible individual animal (genetic predisposition). Another dog eating the same food would be fine as the “high” we are talking about could still be considered to be in the normal range.

A human example would be the dietary changes required for a person who has high cholesterol or some-one with gout. They would show disease or symptoms on certain foods and not on others.

Next month we will discuss heart disease in dogs as another example of nutritionally mediated disease. We will look at recent reports about an association between some pet foods, including some super premium brands, and a heart disease called dilated cardiomyopathy.

Sources: www.fda.gov/animal-veterinary/news-events/fda-investigation-potential-link-between-certain-diets-and-canine-dilated-cardiomyopathy. www.hillspet.co.za/dog-care/healthcare/food-allergies-in-dogs.