Isoflavone concentration of soybean meal from various origins and transfer of isoflavones into milk of dairy cows

The objective of this study was to determine the isoflavone concentration of defatted soybean meals from Argentina, Brazil and USA. Moreover, the transfer of isoflavones from soybean meal into the milk of dairy cows was investigated in a preliminary dose-response study. Six samples of soybean meal from each origin imported into the EU were taken at European harbours and subsequently analysed. The animal experiment was designed as a dose-response study with different amounts of soybean meal. For this purpose, eight lactating German Holstein cows were fed individually with a maize silage based diet containing 0, 10, 20 or 30% soybean meal for five periods over 21 days. At the end of each feeding period, the collected milk was analysed for isoflavones using HPLC-DAD-MS/MS methodology. The average total isoflavone concentrations in mg per kg dry matter in soybean meal were 1570 from Brazil, 1944 from the USA and 3075 from Argentina. Altogether, genistin was predominant with average proportions from 27% (USA) to 39% (Brazil). In milk, genistein was the most prominent phytoestrogen measured at concentrations from 58.9 to 89.8 µg/kg. Furthermore, traces of equol, enterolactone, formononetin and daidzein were detected, particularly, following soybean meal supplementation at high dosage. In conclusion, these results indicate an isoflavone transfer from feed into bovine milk.