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Cow manure could be used to generate power for millions, according to a new US study.
Scientists have calculated for the first time how much of a country's electricity needs could be provided from the manure of cattle and other livestock.
They estimate that 3 per cent of America's total electricity demand could be created from animal waste, enough to power millions of homes and businesses.
Using manure for power could also lead to a significant reduction in the amount of greenhouse gases created, they say.
The study, by scientists at the University of Texas, is published in the Institute of Physics' Environmental Research Letters journal.
Broken down and then burnt, the scientists estimate that the manure from hundreds of millions of livestock in America could produce approximately 100 billion kilowatt hours of electricity a year.
If left to decompose naturally manure releases noxious gases into the environment, some of which warm the atmosphere at a higher rate than carbon dioxide.
Converting it to power could reduce those emissions by 99 million metric tonnes, the equivalent of approximately four per cent of America's emissions from electricity production.
Although the process would emit some carbon dioxide into the atmosphere, it would do so at a lower rate than if coal was used.
Dr Michael Webber and Amanda D Cuellar, who carried out the study, claim that widespread use of manure for energy could reuse "an existing waste source and has the potential to improve the environment".