Abstract

The overall aims of the studies underlying this thesis were to investigate effects of key factors on the concentrations and composition of phytoestrogens and fatty acids in forage species, and effects of differences in their concentrations and composition in forage on their concentrations in bovine milk. In each of the spring cuts, the total isoflavone concentrations in red clover were higher at Umeå than at Skara. At Umeå, the concentration decreased with later cutting time, but at Skara there were no differences between the cutting times. The most abundant isoflavone found in red clover were formononetin, followed by biochanin A. In the summer cuts, the total isoflavone concentration decreased with a longer regrowth interval at Umeå, but this variable was not affected at Skara. Concentrations of each of the analysed isoflavones were considerably higher in red clover than in birdsfoot trefoil. Secoisolariciresinol was only found in birdsfoot trefoil. Meadow fescue had in general higher concentrations fatty acids than timothy. The concentrations of all fatty acids in the grasses decreased with increasing lateness of cutting time in spring cuts. In general, concentrations of C18:0 and C18:1 were higher and concentrations of C16:0, C18:3 and total fatty acids lower in red clover than in birdsfoot trefoil. The concentration of almost all fatty acids decreased with later cutting time. There were correlations between leaf blade proportions, α-tocopherol, β-carotene and protein concentrations, and the fatty acid concentrations. Two similar silage feeding experiments were conducted in which dairy cows were fed silage mixtures. In both experiments, the concentrations of all isoflavones were higher and those of mammalian lignans lower in milk from cows on the red clover-grass diets than in milk from cows on the birdsfoot trefoil-grass or white clover-grass diets. However, the largest observed difference in milk phytoestrogen contents was in the equol concentration. For the fatty acids, the proportions in the milk and recoveries of C18:2n-6 and C18:3n-3 were higher on the red clover diets than on birdsfoot trefoil-grass or white clover-grass diets. Shortening the regrowth interval increased the proportion of unsaturated fatty acids in milk. Supplementation with α-tocopherol increased milk α-tocopherol concentrations but did not affect milk fatty acid composition.