EFFECT OF TREATMENT OF DAIRY-COWS WITH SLOW-RELEASE BOVINE SOMATOTROPIN DURING THE PERIPARTURIENT PERIOD ON MINERALS IN PLASMA AND MILK ANDON PARATHYROID HORMONE-RELATED PROTEIN IN MILK

Slow-release bST was given to dairy cows as a single injection prior t o calving to determine whether such treatment prevented parturient hyp ocalcemia or modified the concentrations of Ca and parathyroid hormone -related protein in milk during the periparturient period. Cows were t reated about 1 wk prepartum, and serial blood and milk samples were ta ken from these and similar prepartum control cows over a 3-wk period. Plasma growth hormone concentrations in the bST-treated group reached a peak 2 d after administration and then declined linearly to control concentrations over a 14-d period. Plasma Ca was unaffected by bST tre atment 1 d prior to parturition, on the day of parturition, and at 1 a nd 6 to 9 d postpartum. Plasma P was higher, and plasma Mg was lower, in the bST-treated group on the day of parturition and 1 d postpartum. Concentrations of Ca, P, Mg, and protein in milk were lower in bST-tr eated cows than in controls at parturition. Milk production of the bST -treated and control groups was similar when measured at d 6 to 9 post partum. Concentrations of parathyroid hormone-related protein in milk were substantial at parturition and remained high thereafter, although at parturition the concentration in the milk of the bST-treated group was lower than that of the control group.