Farmers in the UK are trialling a diet that promises to cut down on the belching coming from cows.

By feeding cows with hay and straw chopped into 6-7cm in length, farmers can cut down on emissions by 20%. The secret is to cut straw or hay into strips and to mix them with silage, wheat, maize, soya or sugar beet. A dairy cow needs only 2kg a day, a tiny percentage of the 60 kilograms of forage it would otherwise eat.

Initial results, in trials on a co-operative of 2,600 dairy farmers producing 16 per cent of Britain’s milk. show that the diet reduced the amount of methane produced per litre of milk from 30 litres to 24 litres. Farmers involved in the trial reported a 15 per cent higher milk yield.

David Beevor, a former professor of animal science who now works for the animal nutritionist Keenan Rumans, said: “The formula is a bit like giving a person a daily breakfast of All-Bran type cereal. The chopped straw or coarse hay adds vital fibre to the diet. Cows then have to chew more on this feed which helps to break it down, increasing the production of saliva and aiding fermentation in the stomach. This enables more feed to be converted to milk.”

Worldwide there are 1.5 billion cattle and their collective belching is thought to account for 5 per cent of all greenhouse gas emissions.