Why a change of diet is good for the environment

BY FEEDING cows and sheep a daily dose of methane-munching bacteria,
researchers in Scotland hope to limit the animals' contributions to global
warming. Methane is one of the most potent greenhouse gases, trapping the
Sun's heat 21 times more effectively than carbon dioxide, the most abundant
greenhouse gas.

Ruminants are responsible for almost a third of all methane pollution in
Europe that passes into the atmosphere. Jamie Newbold and his colleagues at
the Rowett Research Institute in Aberdeen believe they can staunch the flow
by feeding the animals with bacteria that convert methane into less harmful
CO2. "Carbon dioxide is by far the lesser of the two evils," says Newbold.

Ruminants have a four-chambered stomach: in the forestomach, called the
rumen, bacteria make methane as they break down food. The Rowett team
screened a dozen species of bacteria which might produce less gas, by mixing
each in turn with digestive fluid from the rumen. He then exposed the mixture
to methane. The best strain, Brevibacillus parabrevis, converted half the
methane into CO2. "We added methane containing the isotope, carbon-13, and
measured how much of the isotope was switched into carbon dioxide," says
Newbold.

When Newbold added 10 grams of the bacteria to the regular daily diets of
three sheep, methane production went down by around 17 per cent. Newbold
calculates that this could reduce Europe's methane output by 4 or 5 per cent,
more than half the 8 per cent target set for the EU by the Kyoto protocol to
tackle global warming. "It's roughly half what we need to do," he says.