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Potentials to differentiate milk composition by different feeding strategies

T. Slots^*, G. Butler, C. Leifert, T. Kristensen, L. H. Skibsted and J. H. Nielsen^*,1

^* Department of Food Science, Faculty of Agricultural Sciences, University of Aarhus, Blichers Allé 20, PO Box 50, DK-8830 Tjele, Denmark
School of Agriculture, Food and Rural Development, Newcastle University, Nafferton Farm, Stocksfield, Northumberland, NE43 7XD, UK
Department of Agroecology and Environment, Faculty of Agricultural Sciences, University of Aarhus, Blichers Allé 20, PO Box 50, DK-8830 Tjele, Denmark
Department of Food Science, Faculty of Life Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark

¹ Corresponding author: JacobH.Nielsen{at}agrsci.dk

To investigate the effect of the dietary intake of the cow on milk composition, bulk-tank milk was collected on 5 occasions from conventional (n = 15) and organic (n = 10) farms in Denmark and on 4 occasions from low-input nonorganic farms in the United Kingdom, along with management and production parameters. Production of milk based on feeding a high intake of cereals, pasture, and grass silage resulted in milk with a high concentration of -linolenic acid (9.4 ± 0.2 mg/kg of fatty acids), polyunsaturated fatty acids (3.66 ± 0.07 mg/kg of fatty acids), and natural stereoisomer of -tocopherol (RRR--tocopherol, 18.6 ± 0.5 mg/kg of milk fat). A milk production system using a high proportion of maize silage, by-products, and commercial concentrate mix was associated with milk with high concentrations of linoleic acid (LA; 19.7 ± 0.4 g/kg of fatty acids), monounsaturated fatty acids (27.5 ± 0.3 mg/kg of fatty acids), and a high ratio between LA and -linolenic acid (4.7 ± 0.2). Comparing these 2 production systems with a very extensive nonorganic milk production system relying on pasture as almost the sole feed (95 ± 4% dry matter intake), it was found that the concentrations of conjugated LA (cis-9,trans-11; 17.5 ± 0.7 g/kg of fatty acids), trans-11-vaccenic acid (37 ± 2 g/kg of fatty acids), and monounsaturated fatty acids (30.4 ± 0.6 g/kg of fatty acids) were higher in the extensively produced milk together with the concentration of antioxidants; total -tocopherol (32.0 ± 0.8 mg/kg of milk fat), RRR--tocopherol (30.2 ± 0.8 mg/kg of milk fat), and β-carotene (9.3 ± 0.5 mg/kg of milk fat) compared with the organic and conventional milk. Moreover, the concentration of LA (9.2 ± 0.7 g/kg of fatty acids) in milk from the extensive milk production system was found to approach the recommended unity ratio between n-6 and n-3, although extensive milk production also resulted in a lower daily milk yield.

Key Words: organic milk • dairy cow diet • ratio between n-6 and n-3 • antioxidant