Comparison of two alternate PGF2 products in two estrus synchronization protocols in beef heifers.
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Two experiments were conducted to evaluate the effects of a high concentrate, s.c. PGF2 compared with a conventionally concentrated, i.m. PGF2 in estrus synchronization protocols for heifers. In Exp. 1, 869 Angus-based beef heifers were enrolled at 8 locations. All heifers were exposed to the 7-d CO-Synch + controlled internal drug release (CIDR) estrus synchronization protocol. On day 7 of the protocol heifers received 100 g of GnRH i.m., and a CIDR insert for 7 d. On day 0, at CIDR removal, estrous detection patches were applied to heifers and, within location, heifers randomly received 1 of 2 PGF2 treatments: 5 mL of Lutalyse i.m. (CONTROL; n = 434) or a 2 mL of Lutalyse HighCon s.c. (HiCON; n = 435). A second GnRH injection was administered at 54 2 h and heifers were fixed-time AI (TAI). Heifers were evaluated for estrous activity at TAI by determining the activation of estrous detection patches. Pregnancy rates to AI (PR/AI) were diagnosed by transrectal ultrasonography between 35 and 55 d after TAI. The percentage of heifers exhibiting estrus between day 0 and TAI did not differ (P = 0.68) between CONTROL and HiCON treatments (47 vs. 46 4%, respectively). Additionally, PR/AI were similar (P = 0.65) between CONTROL and HiCON treatments (46 vs. 45 3%). In Exp. 2, 190 Angus-based beef heifers were enrolled at 2 locations. Heifers were exposed to the melengestrol acetate (MGA)-PGF2 protocol where they were offered 0.5 mg MGA per day from days 1 to 14. On day 33, heifers were randomly assigned to receive CONTROL (n = 95) or HiCON (n = 95) treatment, and estrous detection aids were applied. Heifers were exposed to AI 12 h after detection of estrus. Heifers not detected in estrus at location 1 received a second PGF2 injection 6 d after the initial PGF2 injection and were placed with fertile bulls. Heifers at location 2 that did not express estrus were administered 100 g of GnRH i.m. and exposed to TAI 96 h after the initial PGF2 injection. Transrectal ultrasonography was used to diagnose PR/AI between 51 and 57 d after the initial PGF2 injection. The percentage of heifers exhibiting estrus during the estrus detection period was similar (P = 0.40) between CONTROL and HiCON treatments (82 vs. 87 4%). Furthermore, PR/AI were similar (P = 0.62) between CONTROL and HiCON treatments (60 vs. 65 5%). In summary, the 2 concentrations and corresponding routes of administration of PGF2 were similar in efficacy at synchronizing estrus in beef heifers.
Oosthuizen, N., Lansford, A. C., Canal, L. B., Fontes, P., Sanford, C. D., Dahlen, C. R., ... Lamb, G. C.
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Oosthuizen, Nicola||Lansford, Alicia C||Canal, Luara B||Fontes, Pedro LP||Sanford, Carla D||Dahlen, Carl R||DiLorenzo, Nicolas||Funston, Rick N||Lamb, G Cliff
