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Hormone Levels in Pre- and Post-Parturient Beef Cows^{1, 2, 3,}

Colorado State University^{5, 6,}, Fort Collins, Colorado 80521

Abstract

Levels of luteinizing hormone (LH), prolactin, estrogens, progestins and corticosteroids were measured in three multiparous beef cows from 3 to 4 weeks prepartum through the second postpartum estrus. Blood was collected daily except at parturition and estrus, when they were collected at 4-hr. intervals from silastic cannulas in the jugular Vein. All cows were suckled following calving. Parturition to postpartum estrus averaged 98 days. LH levels were between 1 and 1.5 ng/ml prepartum; periodic increases up to 3 ng/ml occurred after 2 weeks postpartum until estrus, when a peak of 42 ng/ml occurred 27 hr. before ovulation and declined to between 0.5 to 1.7 ng/ml until the peak at the subsequent estrus. Prolactin levels were below 50 ng/ml during pregnancy but fluctuated from this value to above 300 ng/ml from 2 to 4 days prepartum to 20 days postpartum, remaining between 100 to 200 ng/ml for the rest of the postpartum period studied.

Progestins declined gradually from 10 ng/ml at 3 weeks prepartum to about 2 ng/ml at parturition, fluctuating around 1 ng/ml through most of the postpartum period. Estrogens, in the last 20 days prepartum ranged between 870 and 1,300, fell to 500 pg/ml at parturition and decreased postpartum to about 200 pg/ml and peaked at 500 pg/ml at 2 days before estrus. During the cycle, estrogens fluctuated between 50 and 500 pg/ml with a high at day 5. Corticosteroids varied from 10 to 80 ng/ml between 6 and 21 days prepartum, rising gradually to 116 ng/ml at parturition and falling to 25 ng/ml at 1 day postpartum. Postpartum levels did not appear to be associated with estrus activity.

¹ Published with the approval of the Director of the Colorado State University Experiment Station as Scientific Series Paper No. 1917.

² In partial fulfullment by Graduate Senior Author, of the requirements for the Ph.D. in Animal Science.

³ Research supported in part by Colorado State Project 57 Western Regional Project W-112 Reproductive Performance in Beef Cattle.

⁴ Present Address: Gabriel F. Arije, M.A.N.R., PMB 5007, Ibadan W.S., Nigeria.

⁵ Gratitude is expressed to Dr. E. M. Convey, Michigan State University, East Lansing for the assay of prolactin; Dr. G. D. Niswender, University of Michigan, Ann Arbor, for the rabbit anti-bovine LH serum; Dr. L. E. Reichert, Emory University, Atlanta, Georgia for the purified LH and Dr. W. C. Foote, Utah State University, Logan, for the rabbit anti-estradiol 17-ß serum.

⁶ Departments of Animal Science and Physiology and Biophysics.

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