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Synchronization of Estrus with PGF₂ in Beef Cattle^{1 ,2,}

Montana State University, Bozeman, MT 59717

Abstract

Three estrous synchronization trials were conducted to evaluate the use of PGF₂ for beef. In trial 1, cycling yearling heifers were injected twice 11 days apart with PGR₂ and bred at either 72 and 96 hr or 80 hr after the second injection. The average intervals from the first and second injections to estrus were 53 and 51 hr, respectively. Conception rates at the appointed breeding in the 72/96 hr and 80 hr treatments were 43 and 14% (P<.01), respectively, for all heifers bred and 63 and 19%(P<.01), respectively, for those exhibiting estrus. First service conception rate for the untreated control heifers was 50%. In trials 2 and 3, lactating cows and yearling heifers were divided into treated and control (C) groups. Treated females received PGF₂ and all treated females that exhibited estrus 48 to 96 hr after treatment were bred approximately 12 hr after observed estrus by artificial insemination (T1). Females that failed to exhibit estrus 48 to 96 hr after injection were injected again with PGF₂ 11 days after the first injection (T2). Treatment 2 heifers were bred by appointment at 60 hr post-PGF₂ and cows at 84 hr post-PGF₂. Control females were bred by artificial insemination 12 hr after observed estrus. After the T1 treatment, 50 and 47% of the females were in estrus in trials 2 and 3, respectively. First service conception rates of the Tl females were 67 and 67% compared to 72 and 75% for the C females in trial 2 and 3, respectively. First service conception rates for the T2 females were 58 and 31% for trials 2 and 3, respectively. At the end of the 45-day AI season, 88 and 77% of all treated females were pregnant compared to 87 and 75% of the control females in trials 2 and 3, respectively.

¹ Contribution from Montana Agricultural Experiment Station. Journal Series No. 820. Conducted in cooperation with Western Regional Research Project W-l 12, Reproductive Performance in Cattle and Sheep.

² The authors wish to thank Dr. J. Lauderdale, The Upjohn Company for supplying the prostaglandin F₂ - Tham salt. Dr. S. Webel, Abbott Laboratories for the GnRH and Curtiss Breeding Service for supplying part of the semen used in this study.

³ Northern Agricultural Research Center, Havre, MT.