Plasma levels of vitamin D metabolites in the bovine species during the perinatal period.

Plasma vitamin D metabolites (25-OH D; 24,25-(OH)2D and 1,25-(OH)2D) were measured simultaneously in the blood plasma samples of young cows and their calves. Four of the calves were chronically catheterized in utero at least 2 weeks before the expected time of parturition. No significant hypocalcaemia occurred in the dams at calving. Plasma vitamin D metabolites showed no significant variations for 2 weeks before and 4 days after calving. But rapid changes in plasma 1,25-(OH)2D concentrations were observed in one calf during the first 48 postnatal hours. Before birth, the maternal and foetal concentrations of either 1,25-(OH)2D or 24,25-(OH)2D were positively correlated. 25-(OH) D (13 ng/ml), 24,25-(OH)2D (1 ng/ml) and 1,25-(OH)2D (76 pg/ml) were detected in one foetal plasma collected 35 days before term.