Changes in Ewe's Milk Composition in Organic versus Conventional Dairy Farms

The aim of this work was to determine the effect of organic production system on ewe's milk quality. Bulk tank ewe's milk from flocks of two production systems (organic and conventional) all of them from the same geographical area (Zamora, Spain) were used to investigate changes in physico-chemical properties including the composition in fatty acids. The metal contents (Fe, Cu, Zn, Mn, Se, Mo, Ba, As, Hg, Pb) and the presence of antibiotics and pesticides in the meat were also studied. The type of production system was seen to elicit a significant effect on pH, total acidity and on the fatty acid composition. Organic milk showed significantly higher values of mono- and polyunsaturated fatty acids, including CLA, while saturated fatty acids decreased. No residues of pesticides or antibiotics were found in any of the samples and regarding metal contents only Fe, Cu and Zn were detected and no differences were observed in their contents.