Serum trace minerals in different physiological states of high- and average-producing dairy cows

Two groups of high- and average-producing dairy cows (HPDCs and APDCs, respectively), 50 in each group, were randomly selected from two farms near Shiraz, Fars province, Iran. From each cow in both herds, jugular vein blood samples were collected, 1 month before estimated calving, at calving, and also at 1, 2, and 3 months after calving. Sera were analyzed for zinc, copper, molybdenum, cobalt, manganese, and iron by atomic absorption spectrophotometry. All cows in this study, either during the dry period, following parturition or during the postpartum period were examined for body condition scores and record of reproductive indices. Results showed a significant decline in zinc serum concentrations in high and average producing dairy cows at calving, when compared to corresponding levels of zinc, 1 month before estimated calving (p < 0.05). No significant changes were found in serum zinc concentrations between the HPDCs and APDCs in all states. There was a nonsignificant increase in serum levels of copper at calving in HPDCs and APDCs when compared to the corresponding levels of copper 1 month before estimated calving. The serum concentrations of copper showed no significant variations between HPDCs and APDCs in different states. No significant changes were seen in concentrations of cobalt, manganese, molybdenum, or iron in different states of production. A significant negative correlation between the zinc and copper concentrations (r = −0.32, p < 0.05) was found 3 months after calving in APDCs.