Blood selenium concentration and glutathione peroxidase activity in grazing beef herds with low selenium status

Selenium (Se) deficiency remains a relevant nutritional problem in cattle under Central European conditions, particularly in grazing systems where Se supply depends on soil–plant transfer and the effectiveness of practical mineral supplementation. The objective of this study was to evaluate Se status in grazing beef herds in the Czech Republic using whole-blood Se concentration and glutathione peroxidase (GPx) activity as biomarkers. Three commercial beef-cow herds (Hereford, Simmental, and Angus) were monitored during the grazing season. Blood samples were collected before turnout to pasture (D0) and on d 90 (D90) and d 150 (D150), with 10 cows randomly selected from each herd at each time point. Whole-blood Se concentration and GPx activity were determined, and herd-level reproductive outcomes were recorded. Selenium concentration was affected by sampling day, herd, and their interaction (P < 0.01). At D0, Angus cows had the lowest whole-blood Se concentration (24.65 ± 1.94 µg/L), compared with Simmental (64.32 ± 1.94 µg/L) and Hereford (60.05 ± 1.94 µg/L) cows. At D90, Angus showed the highest Se concentration (152.69 ± 7.44 µg/L), whereas Simmental and Hereford reached 100.68 ± 7.44 and 76.51 ± 7.44 µg/L, respectively. By D150, Se concentrations ranged from 145.69 ± 6.54 to 159.51 ± 6.86 µg/L and did not differ among herds. Whole-blood GPx activity also showed a significant herd-dependent temporal pattern, with the lowest baseline values in Angus, a marked increase at D90, and lower values at D150 relative to Simmental and Hereford. These findings indicate that Se status in grazing beef herds may remain low or suboptimal under practical field conditions despite access to Se-containing mineral licks, and that herd responses during the grazing season can differ markedly. Routine herd-level biomarker monitoring may therefore be useful for evaluating the adequacy of Se supply in grazing beef systems.