Timing GnRH administration with split-time artificial insemination following administration of CIDRbased protocols to synchronize estrus and ovulation in beef heifers and cows
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Split-time artificial insemination (STAI) was developed as a novel breeding strategy that delays insemination by 20 to 24 h for cows and heifers that fail to express estrus prior to a predetermined fixed time. Split-time AI improved pregnancy rates in cows when sex-sorted semen was used in conjunction with the 7-day (d) CO-Synch + CIDR protocol and in heifers inseminated with conventional semen following synchronization of estrus with the 14-d CIDR-PG protocol. It is unclear whether improvements in pregnancy rates after STAI should be attributed to fertility associated effects related to lifespan of sperm in the female reproductive tract when considering the timing of induced ovulations, or to an increase in overall estrous response prior to insemination. These considerations raise questions pertaining to the timing and use of GnRH when STAI is practiced.
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M.S.