Here's a bizarre post about the history of dog powered engines. I'm particularly fascinated by the turnspit dog. That's so cruel!
The Turnspit Dog, 1500-1900 - A dog specifically bred to run on a small wheel in order to turn meat so it would cook evenly. This took both courage, to stand near the fire, and loyalty, to not to eat the roast. Due to the strenuous nature of the work, a pair of dogs would often work in shifts. This most likely led to the proverb “every dog has his day."
Link via Nag on the Lake.