Blood samples for detection of glutathione peroxidase activity and Se concentration were obtained by puncture of thewing vein on days 1, 14 and 49 of the study. Blood was collected into vacutainers containing lithium heparin as anticoagulant.Blood samples were centrifuged (2500 × g for 20 min at 20◦C). Supernatants (plasma) were collected into microtubes andstored at −18◦C for later processing.