Rising Gas Prices in the USA: mules are a viable alternative

At least one US farmer has switched from gasoline engines to mules:
http://www.miamiherald.com/577/story/541830.html

MCMINNVILLE, Tenn. --
High gas prices have driven a Warren County farmer and his sons to hitch a tractor rake to a pair of mules to gather hay from their fields.

[...]

"This fuel's so high, you can't afford it," he said. "We can feed these mules cheaper than we can buy fuel. That's the truth."

[...]

Brother Robert Raymond added, "It's the way of the future."