Research just published at Hewlett Packard’s HP Labs suggests that methane from 10,000 cows would be enough to provide electricity to power for 1,000 servers.
This report provides very little detail to the background of the calculations. But if the cows were fed on grass then they could even be ‘carbon positive’ (or is it negative?) as well. The Carbon Fields by Graham Harvey explains how cows fed on grain (as most are in the USA) are massive consumers of energy and generators of CO2. But if the cows are kept in pasture, and eat grass, more grass then grows, which takes more CO2 out fo the atmosphere. The cows are happier, healthier, and the meat tastes better too.