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Estradiol and Progesterone in Blood Serum during the Bovine Estrous Cycle¹

Michigan State University,^,4 East Lansing, Michigan 48823

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.

¹ Approved by the Director of the Experiment Station as Journal article No. 5638.

² NIH Predoctoral Fellow.

³ Present address: Department of Animal Science, Oregon State University, Corvallis.

⁴ Department of Dairy Science.

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