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

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Abstract
Mammary secretions were sampled prepartum by either milking 1 quarter (4 cows) or 4 quarters (7 cows) twice daily, sampling (15 ml) from 1 quarter once daily (6 cows) or no sampling (5 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. The 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 vs. 1528 .+-. 114 pg/ml), estradiol 17-.alpha. (1173 .+-. 83 vs. 611 .+-. 56 pg/ml) and total estrogen (4191 .+-. 289 vs. 2586 .+-. 148 pg/ml) and higher for estradiol-17.beta. (313 .+-. 23 vs. 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.