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Estrus Synchronization and Subsequent Fertility in Dairy Cattle Treated with 17-Alpha-Ethyl-19-Nortestosterone (Nilevar) and 17-Alpha-Ethynyl-19-Nortestosterone (SC4640)^{1, 2, 3, 4,}

University of Georgia, Athens 30601

Abstract

Twenty daily subcutaneous injections of 5 mg, 10 mg and 20 mg of 17-a-ethynyl-19-nortestosterone (SC4640) dissolved in sesame oil were given to 14 cycling pluriparous cows. A level of 5 mg/d was not sufficient to inhibit estrus in all cases. Levels of 10 mg/d or higher inhibited estrus during the treatment period and appeared to have a prolonged inhibitory period post-treatment in which estrus was suppressed but not ovulation.

Estrus synchronizations were studied in 21 pluriparous cows and 16 heifers given either 17 daily injections of 5 mg/d of 17-a-ethyl-19-nortestosterone (Nilevar) or 7.5 mg/d of SC4640. Ninety percent of the cows were synchronized and exhibited estrus 2 to 4 days post-treatment and 100% of the heifers exhibited estrus 2 to 6 days post-treatment. The 16 heifers conceived from a total of 19 services. Four of the SC4640 treated animals had pregnancies terminated by embryonic death.

¹ Supported in part by a grant from G. B. Searle & Co., who also furnished the Nilevar and SC4640 used in the study.

² The authors wish to acknowledge the technical assistance of N. W. Cameron, of the Northwest Georgia Branch Experiment Station.

³ The authors also want to acknowledge the helpful suggestions of G. E. Short, Director of Animal Products, Searle & Co.

⁴ Journal Series Article No. 722 University of Georgia, College of Agriculture Experiment Station, Athens.

⁵ Present Address: Medical College of Ohio at Toledo, Department of Biochemistry, Toledo.