Mammary Transfer of Hormones and Constituents into Secretions when Cows Were Milked or Secretions Were Sampled Prepartum

Mammary secretions were sampled prepartum by either milking one quarter (four cows) or four quarters (seven cows) twice daily, sampling (15 ml) from one quarter once daily (six cows) or no sampling (five cows). Cows were milked twice daily postpartum. Blood was collected once daily by puncture of the tail vein or artery from 6.9 +--.8 days before calving to 2.5 or 3 days of lactation. Our purpose was to compare hormones in blood plasma, secretions prepartum, and colostrum postpartum. Concentrations of prolactin in secretions and colostrum exceeded those in plasma 2 to 7-fold dependent upon prepartum milking treatment, but groups were not different by 2.5 days of lactation. Concentrations of progesterone in secretions and colostrum averaged 1.4 and 2.6-fold higher than in plasma across groups. Compared with blood plasma prepartum, concentrations in secretions averaged lower for estrone (2705 -+ 223 versus 1528 + 114 pg/ml), estradiol-17alpha (1173 +-83 versus 611 +-56 pg/ml) and total estrogen (419t + 289 versus 2586 + 148 pg/ml) and higher for estradiol-17beta (313 -+ 23 versus 447 +-32 pg/ml). Concentrations of hormones in plasma were correlated with their concentrations in secretions. Prolactin was not correlated with the steroids in blood plasma prior to calving.