Study uncovers differences between organic and conventional milk

Researchers at Newcastle University studied the composition of 22 different milk brands over different years and seasons to establish patterns in their nutritional content.

They found that organic milk had higher concentrations of beneficial fatty acids including polyunsaturated fatty acids and conjugated linoleic acids (CLA).

Specifically the researchers looked at 12 conventional milk brands and 10 organic brands in January and July over two separate years.

Different fats ​

Gillian Butler, who led the study, told DairyReporter.com that the results showed that on average omega-3 levels were 60 per cent higher in organic milk and CLA levels 30 per cent higher. Butler indicated that the differences are explained by the higher quantity of grass and conserved grass in the diet of organic cows – at least 60 per cent under UK regulations.

Commenting on the study, the Department of Health in the UK warned against concluding that organic milk is “better for you”, only that it contains a different mixture of fats from conventional milk.

The study follows on from research that Butler conducted three years ago looking at milk on farms (Journal for the Science of Food and Agriculture​ vol.88, 1431-1441).

In the latest research the differences between the milk types were significant all year round whereas in the previous study the nutritional benefits of organic milk were only proven in summer.

Butler suggested that the newly published results may be more broadly representative as the research looked at the milk that consumers drink and studied different brands, which each pool milk from a number of farmers.

Brand differences ​

As well as allowing the researchers to compare organic and non-organic milk, the study data offered up insight into differences between brands and years.

On the question of brands, Butler said it was not always the more expensive ones that offered the best fatty acid profile. “Some brands – which promote their suppliers as wholesome and grazing on fresh pastures – actually sold milk that appeared to be from very intensive farms.”​

And regarding the year in which the samples were taken, the scientists found that the nutritional profile of the milk was poorer in the summer of 2007 than in the summer of the previous year. In summer 2007 there was three times more rainfall, which would have forced farmers to supplement silage with more concentrated feed and conserved forage.

Butler suggested this could account for the nutritional differences. The scientist added that if wetter summers are to become more frequent as a result of climate change then the finding could be significant.

“If these weather patterns continue, both forage and dairy management will have to adapt to maintain current milk quality.”​

Butler is also conducting research to establish whether supplementation of feed with linseed oil could be an effective way of improving the fatty acid profile of milk.

Source: Journal of Dairy Science
Volume 94, Issue 1, Pages 24-36, January 2011
Fat composition of organic and conventional retail milk in northeast England​
Authors: G. Butler, S.Stergiadis, C. Seal, M. Eyre, C. Leifert