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Luteinizing Hormone, Proclatin, and Interval to Ovulation After Melengestrol Acetate in Cattle¹

Department of Dairy Science and Large Animal Surgery and Medicine, Michigan State University, East Lansing 48823

ABSTRACT

Nine Holstein heifers were fed 1 milligram melengestrol acetate daily for 18 days. After melengestrol acetate withdrawal, duration and magnitude of ovulatory surge of luteinizing hormone resembled that reported for control estrus, and serum prolactin was elevated the day before or on the day of luteinizing hormone surge. In another experiment 25 Holsteins lactating 60 to 90 days were fed 1 milligram melengestrol acetate daily for 14 days and injected with 2,500 international units of human chorionic gonadotropin on day 17. Based upon twice-a-day rectal palpations, 22 cows ovulated at an average of 36±3 hours after injection.

¹ Approved by the Director of the Agricultural Experiment Station as Journal Article 5941.

³ Present address: Dept. of Animal Sciences and Industry, Oklahoma State University, Stillwater 74074.