Influence of organic versus inorganic dietary selenium supplementation on the concentration of selenium in colostrum, milk and blood of beef cows

BACKGROUND Selenium (Se) is important for the postnatal development of the calf. In the first weeks of life, milk is the only source of Se for the calf and insufficient level of Se in the milk may lead to Se deficiency. Maternal Se supplementation is used to prevent this.We investigated the effect of dietary Se-enriched yeast (SY) or sodium selenite (SS) supplements on selected blood parameters and on Se concentrations in the blood, colostrum, and milk of Se-deficient Charolais cows. METHODS Cows in late pregnancy received a mineral premix with Se (SS or SY, 50 mg Se per kg premix) or without Se (control--C). Supplementation was initiated 6 weeks before expected calving. Blood and colostrum samples were taken from the cows that had just calved (Colostral period). Additional samples were taken around 2 weeks (milk) and 5 weeks (milk and blood) after calving corresponding to Se supplementation for 6 and 12 weeks, respectively (Lactation period) for Se, biochemical and haematological analyses. RESULTS Colostral period. Se concentrations in whole blood and colostrum on day 1 post partum and in colostrum on day 3 post partum were 93.0, 72.9, and 47.5 microg/L in the SY group; 68.0, 56.0 and 18.8 microg/L in the SS group; and 35.1, 27.3 and 10.5 microg/L in the C group, respectively. Differences among all the groups were significant (P < 0.01) at each sampling, just as the colostrum Se content decreases were from day 1 to day 3 in each group. The relatively smallest decrease in colostrum Se concentration was found in the SY group (P < 0.01).Lactation period. The mean Se concentrations in milk in weeks 6 and 12 of supplementation were 20.4 and 19.6 microg/L in the SY group, 8.3 and 11.9 microgg/L in the SS group, and 6.9 and 6.6 microgg/L in the C group, respectively. The values only differed significantly in the SS group (P < 0.05). The Se concentrations in the blood were similar to those of cows examined on the day of calving. The levels of glutathione peroxidase (GSH-Px) activity were 364.70, 283.82 and 187.46 microgkat/L in the SY, SS, and C groups, respectively. This was the only significantly variable biochemical and haematological parameter. CONCLUSION Se-enriched yeast was much more effective than sodium selenite in increasing the concentration of Se in the blood, colostrum and milk, as well as the GSH-Px activity.