Fatty acids, carotenoids and fat-soluble vitamin contents in dairy cow milk from autumn grazing in Galicia (NW Spain)

摘要

Pasture growth in Galicia (NW Spain) follows a bi-modal curve, with a maximum in spring followed by a summer drought period, after which the pasture regrowth in autumn makes it possible to extend the cows' grazing season until the winter. The aim of this study was to evaluate the fatty acids (FA) and lipo-soluble antioxidants (AO) content in the milk of dairy cows during the autumn grazing period. A group of eighteen Holstein-Friesian dairy cows rotationally grazed from October to December a 9 ha grass-clover sward where perennial ryegrass was the dominant species. Grazing took place between morning and evening milkings and animals were supplemented indoors during the night with a unifeed mixture made up of maize silage, grass hay and a commercial concentrate. The experiment was divided into two periods, corresponding to the two rotations given to the grazing area. Milk FA and AO concentrations during the grazing period remained fairly constant with no significant difference observed for the main constituents between the two rotations. Average concentrations of polyunsaturated FA, trans-vnccznic FA and c9t11CLA in milk were, respectively, 4.30, 1.62 and 0.81 g 100 g"1 total FA, whilst the milk contents in all-trans-beta-carotene, retinol and a-tocopherol were, respectively, 181, 363 and 992 mugl~(-1).