The Effect of Administering Equine Chorionic Gonadotropins (eCG) on Reproductive Performance of Dairy Cows with a CO-Synch + CIDR Protocol and Insemination at a Fixed Time

The success of a fixed-time artificial insemination (FTAI) program depends on a high ovulation rate during a short interval. Equine chorionic gonadotropin (eCG) has been used in FTAI protocols to improve follicular growth and thereby to produce larger, more responsive follicles for ovulation with increased pregnancy rates. The aim of the present study was to evaluate the effects of eCG on conception rates of early postpartum dairy cows treated by progesterone-based estrous synchronization with artificial insemination at a fixed time (CO-Synch+CIDR protocols). 144 Holstein cows ≥ 55 days postpartum were used. All cows were enrolled in a 7-day CO-Synch + CIDR protocol which included 100 μg gonadotropin releasing hormone (GnRH) at CIDR insertion (day 0); 500 μg prostaglandin F2α (PGF2α) at CIDR removal (day 7); and 100 μg GnRH at FTAI, 66 hours after PGF2α (day 10). Cows were randomly assigned as control cows (n=69) or treated cows (n=75) which received 500 IU eCG at the time of CIDR removal. All cows were examined by ovarian ultrasound at FTAI. The addition of eCG to CO-Synch + CIDR protocols improved the frequency of estrous response (control cows 51.4%, eCG-treated cows 87.8%; P 0.01). It reduced the interval between the end of treatment and the start of estrus (control cows 56.85.52 hours, eCG-treated cows 45.75.87 hours; P 0.01). It increased dominant follicular size at FTAI (control cows 15.1±2.41 mm, eCG-treated cows 19.6±1.84 mm; P 0.001). However, eCG had no effect on pregnancy rates (control cows 49.3%, eCG-treated cows 54.6%; P=0.131). The use of eCG, prior to termination of 7-day estrus synchronization when using the CO-Synch + CIDR program alone, could hasten the time of estrous expression and should be considered in FTAI dairy cows.