There is Gold in them thar Cow Plops!!!
At least that is what this National Film Board short seems to suggest, where an inventor has come up with a good way to extract methane from cow poo, which is usable with cars and such.
The description of the short does it justice:
This short film presents Mr. Bate, an inventor who discovers a substitute for gasoline in barnyard manure. Even though he fits the classic mould of single-minded know-how and practical dreamer, his discovery is tried and tested. He demonstrates how his home-made digester does turn manure into potent methane gas that powers his auto. And for good measure, he demonstrates his latest sustainable invention – a bicycle powered by the bumps on the road.
Now that is what I call a really GREEN solution to a problem, given we need cows anyhow, why not use their DUNG for fun?