Abstract
Jugular blood was collected from 10 Holstein heifers twice weekly from 26 to 6 days before parturitiion, twice daily from 6 days before to 5 days after parturition and on day 9 after parturition. Progestins were extracted from blood serum with trimethyl pentane, glucocorticoids were extracted with dichloromethane, and each was quantified by competitive protein binding assay. Estradiol and estrone were extracted with ether, isolated by column chromatography and determined by radioimmunoassays. Progesterone remained high until —2 days (7.6±.9 ng/ml), fell to 3.0±.7 ng/ml at —1 day and to 0.6±.1 ng/ml at parturition, and remained near this low level for 9 days postpartum. Glucocorticoids remained low until —1 day (6.4±.9 ng/ml), increased dramatically to 10.3±1.5 ng/ml at —.5 day, to 16.7±3.5 ng/ml at parturition, and then fell to 5.1±.8 at 0.5 day after parturition and remained near that basal level for 9 days postpartum. Estradiol increased linearly from 32±6 pg/ml at —26 days to 150±24 pg/ml at —5 days, and jumped to 295±53 pg/ml at —2 and —1.5 days. Then estradiol fell to 52±11 pg/ml at 1 day postpartum and averaged 14±10 pg/ml until day 9 postpartum. Changes in serum estrone generally followed those for estradiol, but estrone was about eight-fold higher. Thus, a 10-fold increase in blood serum estrogens during the month before parturition was the first major change in steroid hormones in advance of parturition. Estradiol, estrone and progesterone all declined precipitously during the final 2 days of pregnancy, while glucocorticoid increased to a peak at parturition. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.