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Control of Estrus and Ovulation using Subcutaneous Implants and Estrogens in Beef Cattle^{1, 2,}

Colorado State University, Fort Collins 80521

Abstract

A subcutaneous implant containing 17-ethyl-19-nortestosterone (Nilevar) was tested to determine its effectiveness in synchronizing estrus and the fertility at the synchronized estrus. Only implants containing Nilevar in the wall were effective in controlling estrus and ovulation. Eighty-seven percent of 15 heifers implanted for 16 days showed estrus in a 96-hr, period compared to 93% of the 42 heifers which were implanted for 9 days and received an injection of estradiol valerate on day of implantation. In the first group of heifers the proportion pregnant at the synchronized estrus was 38% and 61% for heifers implanted for 16 days and 9 days, respectively, compared to 65% for the controls. In the second group of heifers, 50% of the heifers implanted for 9 days were pregnant at the synchronized estrus compared to 69% in the controls (P>.05).

Injection of 2 mg of estradiol-17ß into heifers 24 hr. after removal of an implant which had been present for 9 days and had received an injection of estradiol valerate on the day of implantation caused 98% to 100% of cycling heifers to show estrus in a 48-hr, period and 100% to ovulate in a 36-hr, period. In cows suckling calves, the percent snowing estrus varied from 77% to 94%. Fertility at this synchronized ovulation was lower than that noted in the controls [34% vs. 55% in first group of cycling heifers (P<.05), 10% vs. 44% in 2nd group of cycling heifers (P<05), 54% vs. 67% in 2-year-old cows suckling calves (P>.05), and 67% vs. 75% in 4-year-old cows suckling calves (P>.05)].

¹ Published with the approval of the Director of the Colorado State University Experiment Station as Scientific Series Paper No. 1584.

² Thanks are expressed to G. D. Searle and Co. for support of this project and for supplying the hormones.

³ Department of Animal Science.

⁴ Department of Clinical Science.