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Cortisol and Luteinizing Hormone after Adrenocorticotropic Hormone Administration to Postpartum Beef Cows^1,2,

University of Georgia and US Department of Agriculture, Science and Education Administration, Athens 30602

Abstract

Cortisol and luteinizing hormone (LH) were measured in serum after the administration of adrenocorticotropic hormone (ACTH) to suckled (S) and nonsuckled (NS) beef cows. Blood was sampled on 2 consecutive days every 2 weeks for four bleeding periods starting 14 days after calving. Cows were injected with 200 IV ACTH or saline in a 2-day switchback design. Serum was collected before ACTH or saline injection and at 30-min intervals thereafter for 8 hours. Average Cortisol concentrations in serum were similar in S and NS cows (6.4 ± .6 and 6.1 ± .8 ng/ml, respectively) after saline. Average Cortisol concentrations in serum collected during an 8-hr period after ACTH on days 14, 28, 42 and 56 postpartum were 24.7 ± 2.4, 31.8 ± 3.5, 36.4 ± 4.2 and 40.7 ± .5 ng/ml, respectively, for S cows, and 31.1 ± 2.9, 44.7 ± 5.2, 45.0 ± 5.7 and 46.0 ± 5.4 ng/ml, respectively, for NS cows. Cortisol response to ACTH, measured as area under the response curve, was greater (P<.05) in NS than in S cows. Amount of Cortisol released by 200 IU ACTH was maximal by days 28 to 29 postpartum in NS cows, but the response increased gradually between days 14 to 15 and days 56 to 57 in S cows. Overall, LH in serum averaged .5 5 ± .08 ng/ml for S cows and .92 ± .06 ng/ml for NS cows after saline, and .49 ± .07 ng/ml for S cows and .94 ± .06 ng/ml for NS cows after ACTH. Although mean and peak serum LH concentrations did not differ between cows given ACTH and those given saline, the number of LH peaks and the number of cows having LH peaks were lower (P<.05) after ACTH than after saline. Mean serum LH concentrations were lower (P<.05) in S than in NS cows at 28 days postpartum. The number of LH peaks was lower (P<.05) and the magnitude of the largest LH peak tended to be lower (P<.06) in S cows at all sampling periods.

¹ This research was supported by State and Hatch funds allocated to the Georgia Agr. Exp. Stations.

² The authors wish to thank Dr. E. M. Convey, Michigan State Univ., for LH antisera; Ms. Del Little for statistical help; Georgia Central Branch Exp. Sta. for cattle; Dr. L. E. Reichert for LH for iodination, and the Endocrine Study Section of the National Institute of Health for pituitary hormones used in this study. Appreciation is expressed to Dr. R. S. Lowrey for assistance on this project.

³ Dept. of Anim. and Dairy Sci.

⁴ Present address: Dept. of Anim. Sci., North Carolina State Univ., Raleigh.

⁵ Dept. of Physiol, and Pharmacol., School of Veterinary Medicine.

⁶ Richard B. Russell Agricultural Research Center.