Excellent article, excerpt below:

Healthy weight management

When it comes to healthy weight management prevention is better than a cure, and to prevent obesity, you need to spot it early. There are a few simple things you can do to make sure your dog maintains a healthy weight:

1) Speak to your local vet about your dog's ideal body weight -- they can advise you on feeding amounts as they change from pups through to old age

2) Ensure they get enough exercise -- this will depend on their size and breed type

3) Skip the table scraps -- not all human food is safe for pets and some can even be deadly

4) Weigh your dog -- even slight increases in weight can have a big impact on their health