Presence and changes in the concentration of vitamin D-binding protein throughout early lactation in human and bovine colostrum and milk

Abstract

Synthesis of vitamin D-binding protein (DBP) by explants of ovine mammary gland, and the changes in the concentration of this protein in human and bovine colostrum and milk throughout early lactation have been studied. The changes in the concentration of this protein were similar in human and bovine species. The highest concentration of DBP was found in the first milking (250 μg/ml. and 111 μ/mL for bovine and human colostrum, respectively). The levels of DBP then decreased sharply during the first days of lactation, reaching stable values during the second week postpartum (6 μg/mL and 16 μg/mL, respectively). Milk and plasma DBP were immunologically identical by immunodiffusion and there was no cross-reaction between the two species. DBP synthesis in mammary gland explants could not be detected. The ratio of DBP to albumin in mature milk and especially in colostrum was much higher than in plasma. This could be due to the existence of a specific mechanism in the mammary gland cells for the transference of DBP from plasma to milk.