In most of the holdings of bovine animals play an important role in the changes in the ration during dry period. Especially in the peripartal period is limited to the total supply of feed, what negatively affects on antioxidant indexes in blood of dairy cows (Slavik et al. 2008).

According NRC (2001), diets containing under 0.3 mg of Se/kg of dry matter (DM) per day is deficient for antioxidant effect and immunostimulation of organism in dry period.The objectives of this study were to measure the effect of peroral supplementation of selenium (Se) on the changes of plasma concentrations of Se and glutathione peroxidise (GPx) activities in the blood of dairy cows during peripartal period.

From 240 Holstein herd in a two – four lactation-gestation cycle were selected control group (C) and experimental group (D). The blood samples from vena jugularis were collected 21^st day before calving (control sampling), on the day of calving, 12^th day and 21^st day after calving. The same days after control sampling were peroral supplemented dairy cows in D group with 0.3 mg Se/kg/DM in form of Na₂SeO_3. The control group (C) was without peroral supplementation of Na₂SeO₃ with the diet containing 0.2 mg of Se/kg/DM. The changes (P>0.005) on the concentration of Se in plasma were determined in D group on the day of calving, 12^th day and 21^st day after calving as well as the increased activity of GPx (P>0.05) on the 12^th day and 21^st day after calving in comparison with the control group. 

Key words: dairy cows, supplementation, selenium, glutathione peroxidise, peripartal period

1. Slávik, P., Illek, J., Brix, M., Hlavicova, J., Rajmon, R., Jilek, F. (2008). Influence of organic versus inorganic dietary selenium suplementation on the concentretion of selenium in colostrum, milk and blood of beef cows. Acta Vet. Scan., vol. 50, no. 43, p. 1 – 6.
   NRC, (2001). National Research Council. Nutrient Requirements of Dairy Cattle,6th rev. ed. Washington, D.C.: National Academy Press. Dostupné na internete: http://www.scribd.com/doc/120241792/nrc-2001.