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Hormonal Responses of Dairy Cows with Ovarian Cysts to GnRH^{1, 2, 3, 4, 5, 6,}

University of Missouri⁷, Columbia 65201

Abstract

Twenty-four cows, diagnosed via rectal palpation as having ovarian cysts were randomly assigned to one of four groups to receive a single IM injection of either 0, 50, 100 or 250 µg of synthetic gonadotropin-releasing hormone (GnRH). Sixteen lactating dairy cows exhibiting clinically normal estrous cycles were used as controls.

Of the 18 cows receiving 50, 100 or 250 µg GnRH, 13 (72%) responded to treatment and returned to estrus 20.1 ± 1.5 (range 9 to 27) days after treatment as compared to one of six receiving 0 µg GnRH. Clinical changes in most cases were evidenced by increasing firmness of the cystic structure(s) which subsequently had palpable characteristics similar to corpora lutea.

Plasma LH increased significantly (P<.005) on day 0 in cows following injection of GnRH.

Differences in plasma LH on day 0 between cows responding or not responding to treatment were not significant. Plasma progesterone and estradiol concentrations on day 0 were higher (P<.01) for cows responding to treatment as compared to those not responding.

¹ Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 7176. Approved by the Director.

² These data were presented in part at the 66th Annual Meeting of the American Society of Animal Science, July 28 to 31, 1974, College Park, Maryland.

³ GnRH was generously supplied by Dr. M. D. Brown, Abbott Laboratories.

⁴ Antisera for RIA were generously supplied as follows: luteinizing hormone (LH; B-225) by Dr. G. D. Niswender; progesterone (RDR-9-P) by Drs. R. D. Randel and R. E. Short; and estradiol (RDR-8-E) by Dr. R. D. Randel. Purified bovine LH (LER-1072-2) was generously supplied by Dr. L. E. Reichert.

⁵ The authors wish to express thanks to Mr. Bryan Lail and Mr. Lewis Croy, herdsmen, and Mr. Rich Morgan, farm manager, for their care and observation of the cows used in this experiment. Appreciation is also extended to Mrs. Susan Burpo and Mrs. Karen Kukal for technical assistance and to Mrs. Mary Jane Mottesheard for secretarial assistance in typing of the manuscript.

⁶ This research was conducted as part of regional research project NC-113, Endocrine Imbalances During Abnormal Reproduction in Cows.

⁷ Department of Dairy Husbandry and Department of Veterinary Medicine and Surgery.