Abstract
Levels of estrone, estradiol-17β, and progesterone in the peripheral plasma during late pregnancy and parturition in Holstein cows were measured by specific radioimmunoassay techniques. Estrone levels remained low until 4 weeks prepartum (<155 pg/ml), began to rise from 4 weeks until 1 day prepartum (155-2271 pg/ml), and reached a peak at parturition (2781 pg/ml). Then the levels fell to 197 pg/ml at 1 day postpartum. Changes in the plasma estradiol-17β levels generally resembled those for estrone levels, but the estradiol-17β levels were only 10-21% as compared to those of estrone levels. Progesterone levels remained high until 2 days prepartum (3.71 ng/ml), began to fall, reaching 2.52ng/ml at 1 day prepartum and 0.75 ng/ml at parturition, and was 0.23 ng/ml at 1 day postpartum. On the day of parturition, the levels of estrogens and progesterone remained approximately constant from the beginning of opening labor pains until 1 hr postpartum.
