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Comparing the Fatty Acid Composition of Organic and Conventional Milk

K. A. Ellis^*,1, G. Innocent^*, D. Grove-White, P. Cripps, W. G. McLean, C. V. Howard and M. Mihm^#

^* Division of Animal Production and Public Health, University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow, G61 1QH, UK
Division of Livestock Health and Welfare, University of Liverpool, Faculty of Veterinary Medicine, Leahurst, Neston, CH64 7TE, UK
Department of Pharmacology & Therapeutics School of Biomedical Sciences, Sherrington Buildings, Ashton Street, Liverpool, Merseyside, L69 3GE, UK
Centre for Molecular Biosciences, University of Ulster, Cromore Road, Coleraine, Co. Londonderry, BT52 1SA, UK
^# Division of Cell Sciences, Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow, G61 1QH, UK

¹ Corresponding author: k.ellis{at}vet.gla.ac.uk

During a 12-mo longitudinal study, bulk-tank milk was collected each month from organic (n = 17) and conventional (n = 19) dairy farms in the United Kingdom. All milk samples were analyzed for fatty acid (FA) content, with the farming system type, herd production level, and nutritional factors affecting the FA composition investigated by use of mixed model analyses. Models were constructed for saturated fatty acids, the ratio of polyunsaturated fatty acids (PUFA) to monounsaturated fatty acids, total n-3 FA, total n-6 FA, conjugated linoleic acid, and vaccenic acid. The ratio of n-6:n-3 FA in both organic and conventional milk was also compared. Organic milk had a higher proportion of PUFA to monounsaturated fatty acids and of n-3 FA than conventional milk, and contained a consistently lower n-6:n-3 FA ratio (which is considered beneficial) compared with conventional milk. There was no difference between organic and conventional milk with respect to the proportion of conjugated linoleic acid or vaccenic acid. A number of factors other than farming system were identified which affected milk FA content including month of year, herd average milk yield, breed type, use of a total mixed ration, and access to fresh grazing. Thus, organic dairy farms in the United Kingdom produce milk with a higher PUFA content, particularly n-3 FA, throughout the year. However, knowledge of the effects of season, access to fresh grazing, or use of specific silage types could be used by producers to enhance the content of beneficial FA in milk.

Key Words: organic farming • fatty acid • n-3 fatty acid • conjugated linoleic acid

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