The Nafferton Ecological Farming Group at Newcastle University collected 109 milk samples from 25 commercial farms categorized into the three different production systems: conventional high input; organically certified low input; and non-organic, low input -- not certified organic but using similar organic production methods -- using some mineral fertilizer and shorter withdrawal periods after antibiotic use. These farmers calved all their cows in spring and grazed them throughout lactation, from March until November, resulting in milk being produced on an almost 100 percent fresh grass diet.

Milk from these non-organic farms also had significantly higher levels of nutritionally desirable fatty acids and antioxidants -- resulting from the extensive outdoor rearing and fresh forage intake, study leader Gillian Butler said.

The study, published online in the Journal of Science of Food and Agriculture, found organic milk had higher levels of nutritionally desirable fatty acids of CLA9, omega-3 and linolenic acid, vitamin E and carotenoids and lower levels of undesirable fatty acids such as omega-6 and CLA10.