Q: I am trying to control my nine-year-old Portuguese water dog's weight by feeding her senior/light dog food, controlling the portions, offering low-calorie/low-fat treats and cutting back on table scraps. She still continues to be overweight. Our other dog, a medium schnauzer, who is 10 years old, maintains a healthy weight. Could the fact that our Portuguese water dog eats her own feces contribute to her weight gain?

A: Any excessive caloric intake, whether from too much commercial dog food, low-fat/low-calorie treats, table scraps and even feces, can contribute to weight gain. Weight loss can only occur when more calories are used up than are eaten and your dog is no exception to the rule. The reason your schnauzer does not gain weight may be because of a higher metabolic rate, a more active life style, lower caloric intake or all of these factors.

Stool-eating or coprophagia is common among many animals, not just dogs, and most experts cannot agree on why dogs do it. Some dogs have a genetic predisposition to coprophagia and, in these cases, stool-eating starts between four and 10 months of age and generally stops after one year.

Coprophagic dogs can be divided into two groups: those that eat their own stools and those that eat the stools of other animals. Dogs that eat the stools of other animals are unlikely to be cured of this habit except by preventing access to stools.

Coprophagic dogs that eat their own stools may do so out of boredom or as attention-seeking behaviour. In some cases, the problem may have a medical basis, such as a pancreatic insufficiency and a malabsorption syndrome, two conditions that affect the proper digestion of food. Still other dogs may eat stool in an attempt to recover or retrieve an unabsorbed nutrient or digestive enzymes in the feces. For example, dogs fed diets high in starch and carbohydrate and low in fat and fibre are more likely to eat stool, as are dogs whose diets are primarily dry food or of poor quality.

In your case, it seems that simply feeding low-calorie or low-fat treats and cutting back on table scraps will not be enough. You must cut them out completely. You should also increase the amount of exercise your dog is getting. Also ask your veterinarian for tips on how to curb your dog's stool-eating habits, since this can also contribute to weight gain.

Finally, you may also need to reduce the quantity of light dog food despite what the feeding recommendations on the label say. A recent study of 44 canine and 49 feline commercial weight-control diets by the Cumming School of Veterinary Medicine at Tufts University and published in the Journal of the American Veterinary Medical Association found the caloric density of most of the weight-control diets on the market varied so widely pets would not lose weight and would actually gain weight if owners adhered to the feeding instructions on the labels.

You are wise to be concerned about your dog's weight. Obesity is associated with many diseases including arthritis, heart disease, diabetes, respiratory problems and pancreatitis. Reducing your dog's weight is an effective way to ensure a long and healthy life.