Estradiol and Progesterone in Blood Serum during the Bovine Estrous Cycle

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Abstract
Estradiol was determined by radioimmunoassay and by protein binding assay in blood sera from 11 Holstein heifers during 18 estrous cycles. The two methods gave comparable values (r=0.85), but the radioimmunoassay was more repeatable and had lower blank values. Based upon radioimmunoassay, estradiol increased beginning about 3 days before estrus from an average of 3.6 pg/ml during the luteal phase of the cycle (days 2 to 11) to a peak of 9.7 pg/ml at 0.5 days before estrus. Progesterone and estradiol were correlated significantly (P≃.05) only on the day before estrus (r=−.57). Elevated estradiol preceded the ovulatory LH peak by 1 to 2 days in most heifers, suggesting that estrogen secretion may regulate LH release in cattle. LH and estradiol were correlated (P<.01) only on day −.5 (r=.99) and day 0 (r=.83), and prolactin and estradiol were correlated only on day 7 (r=.73, P≃.01). Relative to values expected in normal heifers, serum LH in two freemartins was about twice that during diestrus, progesterone approximated that during estrus and estradiol resembled that during diestrus. Copyright © 1972. American Society of Animal Science . Copyright 1972 by American Society of Animal Science.

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