If we're adding wheels though, why not attach them to a generator. We could use gearing mechanisms to hook several wheels in line to a single generator. It would take only fairly simple gearing to ensure that unused wheels remained stationary, and ensure the wheels all turned in only one direction, or ignored wheels that were operating in reverse Slightly more complex gearing might allow the dogs to run in either direction and still power something, but I suspect that pack instincts would lead most of them to go in the same direction anyway.

Let's put some more or less arbitrary figures on this. I've seen folks driving around the neighborhood with their dogs on a leash, and as it is a hard thing to keep a car under 5 miles per hour, let us then assume that an average dog can go five miles per hour. As a random guess, I will suppose that an average dog has a weight of about 50 pounds, and is capable of moving it's own weight at this speed.

So now, since there are 5280 feet in a mile, and sixty minutes in an hour, a dog could probably move at a rate of 440 feet per minute, and as it can move it's own weight, I propose that the average "dogpower" would have an output of 22,000 foot pounds per second. horsepower is 33,000 foot pounds per second, meaning that one dog power is equivalent to 2/3 horse power.

With 1 HP equivalent to 746 watts, and generators operating at about 50% efficiency rounding down, a single dogpower puppy mill should be able to produce about 240 watts of power when in use. This means that about four dogs would be able to produce 1KWH of power whenever they ran together. However, it seems likely that dogs would spend only about 1/3 to 1/4 of their time on wheels anyway, so that 16-20 dogs per continuous kilowatt hour seems like a safer figure.

All the same, 20 dogs is a rather modest number for a pound, and I doubt that a pound with only 20 dogs would need more than 10 60 watt bulbs, so depending on AC needs and other electric requirements, there might be some surplus energy to sell through net metering.

Of course, whether hooking up all the gearing and generators, and maintaining the works would really be worth it is another question... But to my knowledge, dog pounds are not noted for turning a profit anyway, so if they can even defray costs with the setup it might be worthwhile.