Regulation of ovarian function in Holstein heifers with SC-21009 IMPLANTS AND ESTRADIOL VALERATE.

The use of implants containing SC-21009 (17alpha-acetoxy-11beta-meth yl-19-nor-preg-4-ene-3 20-dione) a synthetic progestogen was evaluated for control of estrus and ovulation in 16-20 month old Holstein heifers. All heifers were inseminated with semen from 1 collection stored in liquid N2. Implants contained 6-9 mg of SC-21009 i n polyhydroxyethylmethacrylate. This agent for cross-linking was usually mixed at 4.8% concentration of the hormone. Implants 3 mm in diameter and 6-12 mm in length were inserted on the outside of the ear. Each implant was made on a specified day after an observed standing estrus. In Experiment 1 25 heifers were implanted at 2 or 4 days postestrus. These implants were removed after 16 days and the interval to estrus and conception was recorded. In Experiment 2 40 heifers were implanted at 2 or 14 days postestrus with 6 or 9 mg of SC-21009. To more adequately suppress ovarian function estradiol valerate (EV) was given to half of these heifers 7 days after implant insertion and 9 days before removal. In Experiment 3 40 heifers were implanted 2 and 9 days before removal. In Experiment 3 40 heifers were implanted 2 days postestrus with 6 or 12 mg of SC-21009 and a cross-linkage of 4.8%. Some were given no further treatment others were injected with 5 mg of EV in oil and others were implanted with 5 mg of estradiol-17beta in a silastic implant. A few were injected with 15 mg of flumethasone. All of these implants were removed after 9 days and the interval to estrus and fertility was recorded. Experiment 4 was designed to further compare the effects of 6 and 12 mg levels of SC-21009 implanted at 2 and 14 days postestrus with and without 5 mg of EV at implant insertion. At the time of implant removal a Kamar heat detector was placed on each heifer. Those with signs of estrus and those found to have regressed corpora lutea were then inseminated. Experiment 5 was designed to obtain additional information on fertility following implantations and injections of 5 mg of EV at 0 4 8 or 16 days postestrus. Data from Experiment 1 showed no obvious differences in estrous response at 5 days after implant removal as due to dose of hormone or cross-linkage of polymer in those implanted 2 days postestrus. However none of those treated at 14 days postestrus with 7.2% cross-linkage implants were in estrus within 5 days of implant removal. Of 3 treated with 6 mg and 7.2% polymer implants 2 came into estrus while the implants were in place. The highest fertility was obtained with the highest steroid level in Experiment 4 with 12 mg of SC -21009 and 5 mg of EV. This was confirmed in Experiment 5. The percent age of heifers in estrus within 5 days after implant removal increased f rom 50% when implanted at estrus to 70-75% when implanted 2-4 days postestrus. With implantation 8 days or later after estrus all heifers were in heat 5 days after implant removal. When all stages of the estrous cycle are represented equally 85-90% of treated heifers should exhibit estrus within 5 days of implant removal. When implants were made in the winter season the low temperatures interfered with results possible due to the exposed position of the ear.