Pre- and Post-synchronization Methodologies to Enhance the Efficiency of Fixed Timed Artificial Insemination in Pharmacologically-controlled Breeding Systems with Bos Indicus-influenced Cattle

Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the CO-Synch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicus-influenced cattle; 2) Characterize ovarian events associated with the presynchronization; 3) Evaluate the efficacy of measuring vaginal electrical resistance (VER) to assess follicular maturity at TAI; and 4) Compare serum concentrations of progesterone (P4) in ovariectomized cows bearing new or previously used CIDR devices with or without autoclaving. In Exp. 1 and 2, cattle received either GnRH or saline on day -7. The CO-Synch + CIDR protocol included a CIDR insert and GnRH (GnRH-1; day 0), removal of CIDR and PGF2[& alpha] on day 7, and GnRH (GnRH-2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS>̲ 5 tended to differ (P=0.085) between Presynch (38%) and CO-Synch + CIDR (54%). In Exp. 2, ovulatory response to GnRH-1 was greater (P