This study was conducted in a southeast region of Romania, known to be selenium (Se) deficient. The fluorimetric method for the determination of Se in biological samples was used in a study on the serum Se content in time in a group of 10 cows with a high milk yield and in their calves. The same cows were sampled antepartum (late pregnancy) and postpartum (1, 7, 21, 30, and 60 d), and the calves were sampled on d 1 of life and 7, 21, 30, and 60 d postcalving. Colostrum and milk samples were also collected and analyzed at the same times. Throughout the study, the serum Se content in both the cows and the calves was below the reference values 0.040–0.100 μg/mL), except the control conducted 7 d postpartum, for which it was 0.044 ± 0.017 and 0.023 ± 0.007 μg/mL in cows and calves, respectively. The most significant drops were recorded 21 (p < 0.01) and 60 d postpartum (p < 0.05). The colostrum Se was higher (0.036 ± 0.022 μg/mL), decreasing progressively throughout the study to the normal low limit (0.005 μg/mL). The milk Se concentration was lower by approx 78% than the colostrum one on d 1 postcalving. These data demonstrate the course of hyposelenosis both in the cows and their calves. The maternal body proved to “mobilize,” even in case of deficiency, important Se amounts in the colostrum, during the first days in particular.