Hundreds of cattle in Britain are being fed a new diet to reduce their burping and cut emissions of greenhouse gas.

Chopped straw and hay are the vital ingredients to settle a cow's stomach and reduce emissions of methane by 20 per cent.

The secret is to cut straw or hay into strips 6cm-7cm long and to mix them with silage, wheat, maize, soya or sugar beet. A dairy cow needs only 4.4lb (2kg) a day, a tiny percentage of the 130lb daily ration of forage it would otherwise eat.

It is the wind from the mouth of the cow, not the gases from from the rear, that does the most damage to the environment. If every dairy farm in the UK adopted this method it would remove the equivalent of 1.6 million tonnes of CO2 from the atmosphere each year.