Depends on which dog. My retired female doesn't get much excercise at all, and as you would expect is a little heavy, although now extremely overweight. I just feed accordingly, and much to her dismay it isn't as much as she would like.
As for the two who are still in the ring; they primarily get whatever excercise they get when they play. And we do encourage that. We also spend some time several days a week practicing for the ring, which does consist of some jogging.
The most important factor is diet. You have to feed the right diet, and don't feed too much of it. Many "pets" are (over)fed low quality, high carbohydrate diets, which is just like feeding your human kid McDonald's everyday. And we all know what happens if you eat like that all of the time.