Changes in plasma bone metabolic markers in periparturient dairy cows.

We examined fluctuations in plasma tartrate-resistant acid phosphatase isoform 5b (TRAP5b) measured using fluorometry in conjunction with those in calcium (Ca) and other bone metabolic markers from 2 weeks prepartum to 2 weeks postpartum in 7 primiparous and 18 multiparous pregnant cows. The plasma Ca concentration decreased temporarily on the day of calving in multiparous cows only. Plasma TRAP5b peaked on the day of calving in primiparous and multiparous cows and was significantly lower in multiparous cows than in primiparous cows 2 weeks before and after parturition. Plasma hydroxyproline increased 1 week postpartum in multiparous cows. Bone-specific alkaline phosphatase and osteocalcin tended to decrease after parturition in primiparous and multiparous cows. These results suggest that bone resorption increases around parturition in healthy parturient cows from the viewpoint of the TRAP5b activity.