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  • Title: Estrous synchronization strategies to optimize beef heifer reproductive performance after reproductive tract scoring.
    Author: Kasimanickam RK, Whittier WD, Hall JB, Kastelic JP.
    Journal: Theriogenology; 2016 Aug; 86(3):831-8. PubMed ID: 27045628.
    Abstract:
    Three experiments comparing four estrous synchronization protocols were conducted to determine estrous expression rate and artificial insemination pregnancy rate (AI-PR) in heifers with a range (1-5) of reproductive tract scores (RTSs). At enrollment (Day 0), 1783 Angus cross beef heifers from six locations were given body condition score and RTS. The four protocols were: (1) HRTS-DPGF group-heifers with RTS 5 received prostaglandin F2α (PGF; Dinoprost 25 mg; im) on Days 0 and 14; (2) HRTS-CIDR-PGF group-heifers with RTS 5 received a CIDR (1.3-g progesterone) insert on Day 7, followed by CIDR removal and PGF on Day 14; (3) LRTS-CIDR-PGF group-heifers with RTS 4 or less received a CIDR insert on Day 7, followed by CIDR removal and PGF on Day 14; and (4) HRTS-Select-Synch group-heifers with RTS 5 received 100 μg of gonadorelin diacetate tetrahydrate (gonadotropin releasing homone; im) on Day 7 and PGF on Day 14. In all groups, heifers observed in estrus were artificially inseminated (within 120 hours after PGF) using the AM-PM rule. In Experiment 1, estrus expression rates were 82.2% (282/343) and 88.5% (184/208) for HRTS-DPGF and LRTS-CIDR-PGF, respectively (P < 0.05), whereas AI-PR were 51.3% (176/343) and 59.1% (123/208; P < 0.1). In Experiment 2, estrus expression rates were 79.6 (168/211), 86.9 (186/214) and 84.2% (176/209) for HRTS-DPGF, HRTS-CIDR-PGF, and LRTS-CIDR-PGF groups (P > 0.1) and AI-PR were 52.1 (110/211), 60.3 (129/214), and 58.4% (122/209; P > 0.05). In Experiment 3, estrus expression rates were 77.5 (131/169), 85.5 (142/166), and 83.3% (219/263) for HRTS-DPGF, HRTS-Select-Synch and LRTS-CIDR-PGF (P > 0.05) and AI-PR were 53.3 (90/169), 60.2 (100/166), and 58.6% (154/263; P > 0.1). Overall, estrus expression rates for HRTS-DPGF, HRTS-Select-Synch, LRTS-CIDR-PGF, and HRTS-CIDR-PGF groups were 80.4 (581/723), 85.5 (142/166), 85.1 (579/680), and 86.9% (186/214), respectively; higher for heifers in LRTS-CIDR-PGF and HRTS-CIDR-PGF groups compared to heifers in HRTS-DPGF group (P < 0.05). The AI-PR for heifers in HRTS-DPGF was lower (52.0 [376/723]) compared with HRTS-Select-Synch (60.2 [100/166]), LRTS-CIDR-PGF (58.7 [399/680]), and HRTS-CIDR-PGF (60.3 [129/214]); P < 0.05). In conclusion, heifers achieved greater AI-PR after CIDR-PGF or HRTS-Select-Synch estrous synchronization protocols. Even though acceptable AI-PRs achieved in heifers with RTS 5 that were subjected to a double PGF protocol, the reproductive performance was reduced compared with other protocols used in this study.
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