Plasma osteocalcin in preparturient and postparturient cows: correlation with plasma 1,25-dihydroxyvitamin D,...

The purpose of the present study was to determine changes of plasma osteocalcin levels in periparturient cows and to examine the correlation of plasma osteocalcin level with that of 1,25-dihydroxyvitamin D, Ca, and inorganic P. Five Holstein-Friesian cows, aged 3 to 5 yr, were used from 5 d before to 15 d after calving. Concentration (mean +/- SE) of plasma osteocalcin decreased rapidly from d 1 prepartum, reached a low of 8.0 +/- 3.0 ng/ml at d 1 postpartum, and then recovered gradually to 17.8 +/- 3.8 ng/ml at 15 d after calving. In contrast, the concentration of plasma 1,25-dihydroxyvitamin D increased from calving to 3 d postpartum. Plasma concentrations of osteocalcin did not correlate significantly with those of 1,25-dihydroxyvitamin D, but it was significantly proportional to that of Ca and inorganic P. It is suggested that osteoblast function is depressed by a number of factors around the time of parturition.