Overeating is the main reason why dogs become overweight. As with people, when a dog consumes more calories than it uses, its body stores those excess calories as fat. The more fat that accumulates, the heavier your dog becomes.

The amount of exercise or activity your dog gets makes a big difference to how much he or she weighs. Less activity means a greater risk of becoming overweight.

Certain dog breeds are more likely to put on weight than others.  Dogs that are genetically prone to gain weight easily include: Labrador retrievers, Cairn terriers, Cocker spaniels, Cavalier King Charles spaniels, long-haired Dachshunds, Shetland sheepdogs, Basset hounds and Beagles. 

When a dog consumes more calories than it needs for a long period of time, it can lead to obesity. A dog is generally considered obese when its body weight exceeds its ideal weight by 20 percent or more. The risk of obesity increases in pets between the ages of 6 and 12 years, and in pets that have been spayed or neutered.

A fit dog is healthy - and happy. Being the ideal weight allows your dog to move around without difficulty, and get much more out of life. Slim dogs are far less likely to suffer from weight related illnesses like heart disease, diabetes and arthritis and joint problems.

Whatever the cause of your pet's weight gain, it is always advisable to seek the advice and support of your veterinarian.