They have become the fashionable target for environmentalists, but four-wheel-drive vehicles may be less damaging to the environment than the cows and sheep essential to the rural economy.

The methane emissions from both ends of cattle and sheep are causing so much concern in government that it has ordered researchers to find ways to cut down on the emissions from livestock, which account for about a quarter of the methane – a greenhouse gas 20 times more powerful at driving global warming than carbon dioxide – pumped into the atmosphere in Britain. Each day every one of Britain’s 10 million cows pumps out an estimated 100-200 litres of methane.

This is the equivalent of up to 4,000 grams of carbon dioxide and compares with the 3,419g of carbon dioxide pumped out by a Land Rover Freelander on an average day’s drive of 33 miles.

With the United Nations Food and Agriculture Organisation predicting that methane emissions from livestock could increase by as 60 per cent by 2030, the issue is being treated with some urgency.

Scientists attempting to find new foods for cattle have already exploded the myth that most bovine emissions come from the rear. They have found the majority come from belching.

Attempts to find a diet for cattle that will result in less flatulence are being made by researchers as part of a government-backed project.

A study in New Zealand suggested that the methane output could be reduced by up to 50 per cent and small-scale research in Britain has found that “significant quantities” could be prevented from getting into the atmosphere. A Department for Enivonment, Food and Rural Affairs spokesman said: “Recent research suggests that substantial methane reductions could be achieved by changes to feed regimes in farm animals.

“Improving the longevity of dairy cows may also result in decreased methane production as a result of a reduction in the total number of animals needed to produce the same quantity of milk.”

He added that in the longer term the department was also looking at the feasibility of reducing methane from livestock by genetically engineering the digestive system.

Sheep are now being sealed in polytunnels in field experiments to find out if the results of laboratory tests can be matched outdoors. They were chosen in place of cows because they are ruminant but more manageable for research. Mass spectrometers analyse the air in the polytunnels before the sheep eat and the fug afterwards when they have digested their food.

The key to reducing the methane from livestock is, researchers believe, to make the diet of the cattle and sheep more easily digestible.

Michael Abberton, of the Institute of Grassland and Environmental Research in Aberystwyth, said rye grass with a high sugar content, white clover and bird’s-foot trefoil, a traditional meadow flower also known as “bacon and eggs”, all show promise. “Contrary to popular myth the methane comes mainly from belching rather than from the other end,” he said yesterday. “We know the diet of the animal does have an impact on the methane emissions. There are a range of approaches we can take.

“We are, for example, working on high-sugar rye grasses which are designed to increase the effectiveness of the processes in the animal’s gut.”

Particular effort is being put into investigating how bird’s-foot trefoil can be made to grow more abundantly in pastureland as the tannin it contains is thought to be especially helpful in reducing emissions.

The mechanisms within a ruminant’s stomach that produce methane are not fully understood, but the scientists believe that if they make the food more digestible it will reduce the quantity of methane produced by microbes in the gut.

High-sugar rye grass is already on the market, said Dr Abberton, and has improved milk and meat yield from cattle, but new strains of grass and clover are under development to make them more digestible to reduce the impact of livestock on climate change.

The team of scientists, funded by Defra, believe that farmers will need to be shown additional advantages if they are to be persuaded to go to the expense of introducing new strains.

The £750,000 project, led by the University of Wales, Aberystwyth, will run for three years and will also consider how emissions of nitrogen, another greenhouse gas, can be reduced in livestock. Agriculture accounts for 37 per cent of methane and 67 per cent of nitrous oxide emissions in Britain.

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