The effect of inorganic and organic selenium added to diets on milk yield, milk chemical and mineral composition and the blood serum metabolic profile of dairy cows

The study was to determine the effect of Se in its inorganic (sodium selenite) compared to organic (selenised yeast, Saccharomyces cerevisiae) forms added to a grass-plus maize-silage based diet on milk yield, milk composition and blood serum metabolic profile of dairy cows. The experiment lasted for 90 days between 150 and 240 day of lactation (SD=26) to avoid the burden connected with high milk productivity in the beginning and at the peak of lactation. One group of cows was supplemented with the mixture containing inorganic Se (sodium selenite), while in the organic treatment the mineral-vitamin mixture was identical except for no sodium selenite added, with Se included in the form of selenised yeast (6 g of yeast/cow/day = 6 mg Se/cow/day). After 90 days of the experiment no differences were observed between the treatments in the amount of fodder consumed, daily milk yield or milk components. However, the cows under the Se organic treatment had higher overall milk production (20%). Selenium concentration in milk from the organic selenium treatment was increased by over 300% compared to the inorganic Se treatment. There were no differences in blood serum biochemical parameters and the activity of lysosomal enzymes between treatments. Thus, the Se yeast supplementation at 6g per day has no negative effect on the health status of dairy cows. Milk of all cows had a FPD closer to 0 degrees C at 150 vs. 240 days of lactation. It might mean that the organisms still underwent some physiological disturbances associated with high milk production.