It would be neat if there was a way to generate mechanical power using animals as power source.
See: horse mill or any other animal engine.
The animals would push/pull a horizontal axle around a center point to drive the vertical axle in the middle.
Different suggestions for the inner workings:

1. Different animals result in different power outcomes (Mechanical Power Produced: Horse>Donkey>Cow>Other).
2. Animals need to be fed (love mode?) to be able to push. This would make it a bit more difficult to use.
3. Push axle: Animals have to walk against the horizontal axle.
   Pull axle: Animals have to be tied to the horizontal axle and walk a slight bit in front of the axle.