The objective of this study was to evaluate, in grazing dairy heifers, the effect of an oral bolus on plasma trace mineral status. Heifers (n = 74, initial BW = 427 kg, age = 445 d) from 4 dairy farms in Western France, were randomly assigned to a control group (CONTROL) and a trial group (TEST). Heifers in TEST received 2 boluses (Dietevit Excell, Néolait, Yffiniac, France), at the start of grazing season. Boluses supplies zinc, manganese, copper, iodine, cobalt, selenium, vitamin A, vitamin D3 and vitamin E. Blood samples were taken before turn out in April (d 0), in July (d 106), and at the end of the grazing season in November (d 245). Plasma trace minerals analysis was carried out by ICP-MS (LEA Vendée, France). Glutathione peroxidase was also measured (LDH, Oniris, France). Metabolic profiles were compared using Repeated Measures ANOVA (SPSS v18). Samples of grass were taken from the grazing plots and were analyzed by ICP-MS (Sciantec Analytical Services Ltd., United Kingdom). Grass trace mineral content per kg DM was zinc (25.4 mg), manganese (84 mg), iron (72 mg), copper (5.3 mg), cobalt (0.10 mg) and selenium (0.03 mg). Compared with CONTROL, heifers in TEST had the same trace minerals levels in d 0, higher selenium levels (42.6 vs. 25.7 µg/L in d 106 and 36.4 vs. 26.6 µg/L in d 245, P = 0.01 and P = 0.03), higher glutathione peroxidase levels (205 vs. 114 µg/L in d 106 and 205 vs. 129 µg/L in d 245, P = 0.01 and P = 0.02) and higher iodine levels (79 vs. 48 µg/L in d 106 and 62 vs. 56 µg/L in d 245, P = 0.01 and P = 0.07). There was no difference in plasma level for zinc (1064 vs. 999 µg/L in d 106 and 954 vs. 922 µg/L in d 245), manganese (2.8 vs. 2.8 µg/L in d 106 and 3.3 vs. 3.4 µg/L in d 245), copper (892 vs. 916 µg/L in d 106 and 995 vs. 1017 µg/L in d 245) and cobalt (1.4 vs. 1.2 µg/L in d 106 and 1.1 vs. 0.9 µg/L in d 245). Administration of 2 Dietevit Excell boluses to dairy heifers before turn out maintains healthy selenium, glutathione peroxidase and iodine plasma levels over a period of at least 245 d. Results show that Dietevit Excell gradually dissolves providing a sustained release of minerals over the grazing season.