Enhancing the selenium content of bovine milk through alteration of the form and concentration of selenium in the diet of the dairy cow

Since estimated dietary selenium intake in the UK has declined steadily from around 60 (mu)g day^-1 in 1975 to 34 (mu)g day^-1 in 1997, there is a need to increase selenium intake from staple foods such as milk and milk products. An experiment was therefore done to investigate the relationship between dietary source and concentration of selenium and the selenium content of bovine milk. In a 3 × 3 factorial design, 90 midlactation Holstein dairy cows were supplemented over 8 weeks with either sodium selenite (S), a chelated selenium product (Selenium MetasolateTM) (C) or a selenium yeast (Sel-PlexTM) (Y) at three different dietary inclusion levels of 0.38 (L), 0.76 (M) and 1.14 (H) mg kg^-1 dry matter (DM). Significant increases in milk selenium concentration were observed for all three sources with increasing inclusion level in the diet, but Y gave a much greater response (up to +65 (mu)g l^-1) than the other two sources of selenium (S and C up to +4 and +6 (mu)g l^-1 respectively). The Y source also resulted in a substantially higher apparent efficiency of transfer of selenium from diet to milk than S or C. Feeding Y at the lowest dietary concentration, and thus within the maximum level permitted under EU regulations, resulted in milk with a selenium concentration of 28 (mu)g l^-1. If the selenium concentration of milk in the UK was increased to this value, it would, at current consumption rates, provide an extra 8.7 (mu)g selenium day^-1, or 11 and 14% of daily recommended national intake for men and women respectively.