Cut down on flying, sell the car and recycle your bottles. But if you really want to tackle global warming, you should stop your cow from burping.

According to scientific estimates, the methane gas produced by cows is responsible for 4% of greenhouse gas emissions. And now, German scientists have invented a pill to cut bovine burping.

The fist-sized plant-based pill, known as a bolus, combined with a special diet and strict feeding times, is meant to reduce the methane produced by cows.

"Our aim is to increase the wellbeing of the cow, to reduce the greenhouse gases produced and to increase agricultural production all at once," said Winfried Drochner, professor of animal nutrition, who has led the ground-breaking project at the University of Hohenheim in Stuttgart. "It is an effective way of fighting global warming."

Prof Drochner wants to use the pill to trap some of the energy from the methane, which is naturally produced in the fermentation process when a cow digests grass and is later mostly burped out through their mouths. Until now it has been wasted.

"We could use the energy to boost the cow's metabolism," he said. The idea is that the cows would use the methane to produce glucose instead of passing it as wind. In turn this should help them to produce more milk.

"The fist-sized tablets mean that microbiotic substances can slowly dissolve in the cow's stomach over several months," said Prof Drochner.

Over the past 50 years the concentration of methane in the atmosphere has increased six-fold. With meat consumption growing, it is set to rise further.