Comparison of long-term progestin-based protocols to synchronize estrus in beef heifers

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Experiment 1 evaluated two long-term progestin-based and controlled internal drug release estrus synchronization protocols to determine their potential to facilitate fixed-time artificial insemination in estrous cycling and prepubertal beef heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ between treatments. Experiment 2 compared two long-term progestin-based estrus synchronization protocols to evaluate their potential to facilitate fixed-time artificial insemination in estrous cycling and prepubertal beef heifers. Estrous response after PG was greater among CIDR treated heifers compared to MGA treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ between treatments. In summary, the long-term CIDR protocol compared favorably with the MGA protocol. Experiment 3 was conducted to compare pregnancy rates resulting from fixed-time AI after administration of either one of two long-term CIDR-based protocols. CIDR-GnRH-PG and CIDR-PG treated heifers were fixed-time inseminated at 72 or 66 hr after PG, respectively. Fixed-time AI pregnancy rates tended to be higher among CIDR-PG compared to CIDR-GnRH-PG treated heifers. Final pregnancy rates did not differ between treatments. In summary, both long-term progestin-based protocols were effective in synchronizing estrus prior to fixed-time AI in beef heifers.