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Concurrent Changes in Bovine Plasma Hormone Levels Prior to and during the First Postpartum Estrous Cycle^{1, 2,}

Cornell University⁴, Ithaca, New York 14850

Abstract

Plasma estradiol, estrone, progesterone, total corticoids and LH levels were measured in samples collected at 4-day intervals from 35 postpartum and cyclic lactating cows. Estrogens were extracted, purified on Sephadex LH-20 columns and quantitated by a radioimmunoassayusing ovine anti-estradiol and dextran coated charcoal separation. Progesterone and total corticoids were measured by a competitive protein binding assay. LH levels were determined by a double antibody radioimmunoassay procedure.

Plasma estradiol concentrations were elevated at parturition (67.9 ± 24.4 pg/ml) as compared to 4 days later (10.3 ± 4.3 pg/ml plasma). Plasma corticoid levels also decreased following parturition. Plasma progesterone and LH values remained at a low level (0.0 to 0.3 ng/ml plasma and 0.5 to 3.0 ng LH-B7/ml plasma, respectively) from parturition until first estrus.

Estradiol concentration began to rise 2 to 3 days prior to estrus, but declined rapidly after estrus. Changes in plasma estrone levels paralleledthose of estradiol. Preovulatory LH peaks ranged from 7 – 55 ng LH-B7/ml of plasma with levels of 0.5 – 3.0 ng during the remainder of the cycle.

¹ Portions of this study were presented at the American Dairy Science Association meetings, 1971, and included in a review of hormone levels during the estrous cycles of domestic animals presented at the American Association for the Advancement of Science meetings, 1971. This research was supported in part by the cooperative regional research project NE-41 and by NIH Training Grant in Reproductive Physiology HD-00171.

² Appreciation is expressed to Dr. Leo E. Reichert for highly purified bovine LH (LER-1072-2), Dr. G. D. Niswender for the anti-bovine LH serum and the Endocrine Study Section of the National Institutes of Health for providing the NIH-LH-B7 standard.

³ Present address: U. S. Meat Animal Research Center, Clay Center, Nebraska 68933.

⁴ Department of Animal Science, Division of Biological Sciences.