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R. E. Monn, J. C. Mackey, H. B. Dudley, D. H. Poole, 115 Effect of a Pre-Synchronization Protocol on Beef Heifer AI Pregnancy Rates, Journal of Animal Science, Volume 95, Issue suppl_1, December 2016, Pages 56–57, https://doi.org/10.2527/ssasas2017.0115
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Abstract
Success of a cow-calf operation starts with proper development of replacement heifers. Advancements in reproductive technologies have improved pregnancy rates in replacement heifers. There are several estrous synchronization protocols available to achieve acceptable AI pregnancy rates for beef heifers; however, undesirable consequences leading to reduced fertility can occur if heifers are prepubertal or not responsive to hormonal stimulation. Greater pregnancy rates have been observed in heifers exhibiting 3 estrous cycles prior to insemination compared to pubertal heifers. In effort to improve fertility, the objective of this project was to compare the effectiveness of a presynchronization program prior to the 5d CO-Synch+CIDR FTAI protocol. Angus and SimAngus heifers approximately 60% of mature BW (n = 95) at 2 locations were randomly assigned to be synchronized using the 5d CO-Synch+CIDR protocol (control) or to receive a presynchronization program consisting of 2 injections of PGF2α administered 25 and 11 d prior to the start of the 5 d CO-Synch+CIDR protocol (treatment). All heifers were artificially inseminated 60 h after CIDR removal. Heifer BW, age, BCS, Reproductive tract scores (RTS) and pelvic area were measured at 25 d prior to the start of the 5 d CO-Synch+CIDR protocol. Blood samples were collected 3 consecutive times at 7 d intervals to determine the onset of puberty via analyzing serum progesterone concentrations. Pregnancy status was assessed by ultrasonography 30 d post-insemination. Data were analyzed using a MIXED procedure of SAS and examined for effects of treatment, RTS, pelvic area, BCS, location, and age. Statistical significance was determined at P < 0.05 and a tendency at 0.05 < P < 0.10. While there was no difference between treatments, more heifers were cycling prior to the start of the estrous cycle at location 1 compared to location 2 (78.6% vs. 50%, respectively). Implementing a presynchronization program prior to the 5d CO-Synch+CIDR protocol significantly reduced AI pregnancy rates (P < 0.05) compared to controls (34.9%, 58.5%, respectively). Heifer BW, age, breed, BCS, pelvic area or location did not affect (P > 0.05) AI pregnancy rates. Heifers with a RTS of 3 or 5 at the start of the 5d CO-Synch+CIDR protocol had greater AI pregnancy rates (P < 0.05) compared to heifers with a RTS of 4 (48.2%; 62.4% and 29.5%, respectively). The addition of the presynchronization program disrupted cyclicity in treated heifers without noticeable changes in the development of the reproductive tissues. Based on the data, incorporating presynchronization breeding programs is not recommended for improving pregnancy success in replacement heifers.
