Effect of Sodium Selenite, Selenium Yeast and L-selenomethionin Supplementation on Milk and Blood Selenium Concentrations in Dairy Cattle

Selenium is an important component of the enzyme, glutathione peroxidase, which plays a crucial role in the cellular antioxidant system (Rotruck et al 1973). In this way, adequate Selenium (Se) levels support the cellular antioxidant system and are beneficial for dairy cattle health and fertility. Since many regions in the world have soils with low Se content, supplementation of this trace element is very often warranted to reach an advised daily Se intake of 0.3 mg/kg DM complete diet (NRC 2001). The aim of the present study was to evaluate 3 different Se sources: sodium selenite (NaSe), selenium-yeast (SeYeast) and L-selenomethionine (SeMet) in their potential to achieve adequate blood and milk Se levels. A feeding trial was set-up with 26 high producing Holstein Friesian cows. After a 2 week pre-treatment period without Se supplementation, cows were divided in 4 homogeneous groups based on lactation number, milk production, milk composition and liveweight, and received either no supplementation (Ctrl) or 0.3 mg/kg dry matter intake (DMI) of either NaSe, SeYeast or SeMet for the next 7 weeks. Cows were given maize and prewilted grass silage ad libitum (60/40 on DM base), a mixture of soybean-meal and rapeseed-meal (65/35) to equalize energy and protein intake and a balanced concentrate. Milk and blood serum samples were taken during the pre-treatment period (week 0) and at week 3 and 7 after the start of supplementation. Blood serum Se concentrations were analysed by atomic absorption spectrometry. Milk Se concentration was determined by inductively coupled plasma mass spectrometry. Blood serum Se and milk Se data have been analysed using a linear model within week (p<0.05). Additionally, the longitudinal nature of the Se data was modelled in a longitudinal regression model (Proc MIXED in SAS version 9.3. for windows). DMI was constant during the trial. Milk production was 29.9kg in Ctrl, 31.6kg in NaSe, 28.3kg in SeYeast and 27.8kg in SeMet cows. The LM showed that mean blood serum Se and milk Se concentrations were initially not different between groups but were affected by selenium source at week 3 and 7 (Table 1). The longitudinal model showed that, after 3 weeks of supplementation, blood serum Se increased significantly stronger for SeMet and SeYeast in comparison with NaSe and milk Se increased significantly stronger for SeMet in comparison with SeYeast and NaSe. The negative quadratic term indicated that both blood serum and milk Se reached a plateau phase as the trial progressed. After 7 weeks of supplementation Se levels in blood were equally high for the 3 Se sources and Se levels in milk were intermediate for SeYeast, highest for SeMet and lower for NaSe The increase in milk Se is strongly related to the proportion of SeMet in the Se source and therefore Se transfer to the milk is better for both organic sources, SeMet and SeYeast in comparison with NaSe, which is in line of what Ceballos et al (2009) showed. In conclusion, the increase in milk Se content is significantly determined by the source of Se used, with SeMet leading to a faster increase, followed by SeYeast.