Milk from organic cattle that eat a fresh grass diet is likely to be better for your health, according to a new study by the University of Newcastle

This organic milk contained more good fatty acids such as omega-3 and conjugated linoleic acid known as CLA9 than milk produced at intensive commercial dairy farms. The difference was even more marked during the summer with levels of CLA9 about 60 per cent higher in milk from cattle that graze in fields.

Gillian Butler, livestock project manager for the university's Nafferton Ecological Farming Group, who led the research, said: “Our work has not looked at the impact on human health, but I would say organic milk should be better for health from what we know of the benefits of these good fatty acids. She added: “They are effective in combating cancer, coronary heart disease and type II diabetes.”

The sampling of milk took place during 2004 and 2005 but the results were published only yesterday in the Journal of Science of Food and Agriculture.

Mrs Butler, 53, said that she had switched to drinking organic milk three years ago after analysing the data. “My interest now is that if we can improve the quality of milk we can also improve the health qualities of butter and cheese,” Mrs Butler said.

Organic cattle in the South of England spent most of their lives out of doors but in the North and Scotland cattle are brought indoors to live in sheds from the end of September or October, depending on rain and cold temperatures.

Researchers found that by adding a mix of soya beans, rapeseed and linseed to the daily food rations for each cow kept indoors, milk quality improved and was comparable to the milk from an outdoor cow eating a fresh grass diet.

“We've shown that significant seasonal differences exist. Our future research is focusing on how to improve the nutritional composition of milk during the winter, when cows are kept indoors and fed mainly on conserved forage,” she said.

The study, which was a collaboration between scientists at Newcastle and the Danish Institute for Agricultural Science, is part of a European Commission-funded project about milk quality and minimising use of antibiotics in dairy production. The scientists also discovered interesting results from a group of non-organic farms that used similar production methods to organic systems.

These cattle lived outdoors from March until November, eating almost a 100 per cent fresh grass diet. This milk had higher levels of the good fatty acid CLA9, whereas organic milk had higher levels of omega-3.

Further work is under way but Mrs Butler believes that the difference is linked to the amount of clover in fields. Organic farms have more because they do not use fertilisers.

The findings delighted the Soil Association, which champions organic food and farming in Britain.

Peter Melchett, policy director at the the association, said: “This research confirms what organic farmers and consumers have long believed to be true.

“Some sceptics have thrown doubts on the benefit of organic milk because scientists had not shown precisely how organic farming makes a positive difference. This latest research demonstrates that it is the cows' organic diet that makes their milk healthier. Other research has shown the same is true for beef and lamb reared on grass.”

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