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.

This material is used as bedding for cattle and cows usually have little appetite for it. But just as children are coaxed to take their medicine by cloaking it in a syrup, cattle are being fed a blend of foods that makes it irresistible.

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.

The dairy industry is excited by the development and is now hoping that every dairy farmer in the country will take it up.

Dairy UK, an organisation that represents the sector, is striving to create a greener pint of milk as part of the government targets to combat climate change.

Initial results show that the diet reduced the amount of methane produced per litre of milk from 30 litres to 24litres in trials on farms attached to First Milk, a co-operative of 2,600 dairy farmers producing 16 per cent of Britain's milk.

Farmers involved in the trial reported a 15 per cent higher milk yield. The average production is 24 litres a day but this increased by three or four litres. 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.” Gerald Watkin, 48, who farms at Borth, near Aberystwyth, Mid-Wales, has 140 dairy cattle and has been giving his herd the new feed mix for a year. He has been amazed by the results of a higher milk yield and helping to reduce greenhouse gases.

He said: “If I put out yellow straw for them the cows would not touch it. They might play with it like a child who won't eat his greens.

“But with this feed mix they can't pick out the straw. The cattle also seem more contented and are chewing the cud longer because they have more fibre. Their health has also improved and lameness is less of a problem and milk yield is up.”

Jim Begg, director of Dairy UK, said: “Everyone knows that cows produce methane and the presumption is that nature must take its course.

“But this terrific initiative shows how we can make the dairy sector even greener, and give consumers the low-carbon products they want.”

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

Dairy UK is also working to reduce nitrogen and water use on farms, pioneering renewable energy plants, cutting packaging waste and improving distribution to cut down on fuel and transport.

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