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Regulation of Ovarian Function in Holstein Heifers with Sc-21009 Implants and Estradiol Valerate^{1, 2,}

University of Connecticut, Storrs, 06268

Abstract

Two-hundred and fifteen Holstein heifers were used in five experiments to evaluate the use of implants containing SC-21009 (17-acetoxy-11β-methyl-19-norpreg-4-ene-3,20-dione), a synthetic progestogen, alone or in combination with an injection of estradiol valerate for the control of estrus and ovulation. Two experiments were conducted using a 16-day implant period. In Experiment I, it was observed that heifers implanted 14 days postestrus and in heat within 5 days after implant removal had lower fertility (none of eight conceived to first service) than did those implanted 2 days postestrus and in heat within 5 days after implant removal (nine of 13 conceived to first service). In Experiment II, estrus and ovulation were not suppressed in most heifers implanted 14 days after estrus. This occurred during the winter with temperatures consistently below freezing.

Three experiments with 9-day implant periods were conducted. In Experiment III, the number of heifers with an estrous cycle less than 17 days in length following implantation on days 2 through 11 was greater in heifers implanted with 12 mg SC-21009 than in heifers implanted with 6 milligrams. In Experiment IV, the data indicated that the highest fertility, as well as the greatest number of heifers in heat within 5 days after implant removal, was obtained in those heifers treated with 12 mg SC-21009 and 5 mg estradiol valerate. In Experiment V, fertility of heifers treated 0, 4, 8 or 16 days postestrus with 12 mg SC-21009 and 5 mg estradiol valerate was compared with untreated control heifers. The percent conception at first service of treated heifers (60.8%) did not differ from that of control heifers (63.6%).

¹ Scientific Contribution No. 576, Agricultural Experiment Station, University of Connecticut, Storrs.

² Supported in part by grants from Eastern Artificial Insemination Cooperative and G. D. Searle and Co. Also semen was supplied by the former and hormones were supplied by the latter.

³ The authors would like to thank the following for their help and cooperation: D. A. Grant, D. Avery, H. Schaid and F. Schaffer.