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We evaluated the effect of an additional prostaglandin F2α (PGF2α) treatment at the initiation of a 7-d CO-Synch + CIDR synchronization of estrus protocol in a Split-time AI program. Our objective was to determine if estrus response and fixedtime AI (FTAI) pregnancy rate could be enhanced by eliminating existing corpora lutea at the beginning of synchronization. Postpartum (>80d), multiparous commercial Angus cows (n =100) on a large ranch in West Texas were randomly allocated by age (5.31 ± 2.15 yr) to one of two treatments: 1) cows (n = 52) received PGF2α (25 mg) + GnRH (100 µg) and a 7-d CIDR (+PG) on d0 or 2) cows (n = 48) received GnRH (100 µg) and a 7-d CIDR (Control) on d0. All females received PGF2α (25 mg) and Estrotect® patch for evidence of estrus at CIDR removal (d7). All animals were gathered and worked through a chute at random, beginning 70 h post- CIDR removal. Cows were considered estrual (EC) when either the majority (> 50%) of patch showed color or if the patch was absent. Estrual cows received FTAI 70 to 73 h after CIDR removal. Non-estrual cows received GnRH (100 µg) 70 to73 h after CIDR removal and were FTAI 78 to 79 h after CIDR removal. Beefmaster sires (n=4) were equally represented across treatment and technician at FTAI. Pregnancy to FTAI was determined utilizing real-time ultrasound 35 d after FTAI. Data were analyzed using PROC FREQ of SAS. Overall, FTAI pregnancy rate and estrus response were 58% and 68%, respectively. Pregnancy rate for Control EC was greater (80.78%) than +PG EC cows [66.67%, (P < 0.05)]. Pregnancy rates for non-estrual cows were similar (P > 0.05) among +PG (50%) and Control treatments (40.91%). Pregnancy rates across sires were similar (P > 0.05). Estrus response to treatment was analyzed using PROC GLIMMIX of SAS. Estrus response was greater (P < 0.02) for +PG cows (76.92 ± 5.84%) than for control cows (54.17 ± 7.19%). These results indicate that, PGF2α administration at CIDR insertion and removal in a7-d CO-Synch + CIDR protocol for a Split-time AI program improved estrus response. However, pregnancy rates were lower and may have been influenced by the timing modification of FTAI to the Split-time AI program implemented. [ABSTRACT FROM AUTHOR]

We evaluated the effect of an additional prostaglandin F2α (PGF2α) treatment at the initiation of a 7-d CO-Synch + CIDR synchronization of estrus protocol in a Split-time AI program. Our objective was to determine if estrus response and fixedtime AI (FTAI) pregnancy rate could be enhanced by eliminating existing corpora lutea at the beginning of synchronization. Postpartum (>80d), multiparous commercial Angus cows (n =100) on a large ranch in West Texas were randomly allocated by age (5.31 ± 2.15 yr) to one of two treatments: 1) cows (n = 52) received PGF2α (25 mg) + GnRH (100 μg) and a 7-d CIDR (+PG) on d0 or 2) cows (n = 48) received GnRH (100 μg) and a 7-d CIDR (Control) on d0. All females received PGF2α (25 mg) and Estrotect® patch for evidence of estrus at CIDR removal (d7). All animals were gathered and worked through a chute at random, beginning 70 h post- CIDR removal. Cows were considered estrual (EC) when either the majority (> 50%) of patch showed color or if the patch was absent. Estrual cows received FTAI 70 to 73 h after CIDR removal. Non-estrual cows received GnRH (100 μg) 70 to73 h after CIDR removal and were FTAI 78 to 79 h after CIDR removal. Beefmaster sires (n=4) were equally represented across treatment and technician at FTAI. Pregnancy to FTAI was determined utilizing real-time ultrasound 35 d after FTAI. Data were analyzed using PROC FREQ of SAS. Overall, FTAI pregnancy rate and estrus response were 58% and 68%, respectively. Pregnancy rate for Control EC was greater (80.78%) than +PG EC cows [66.67%, (P < 0.05)]. Pregnancy rates for non-estrual cows were similar (P > 0.05) among +PG (50%) and Control treatments (40.91%). Pregnancy rates across sires were similar (P > 0.05). Estrus response to treatment was analyzed using PROC GLIMMIX of SAS. Estrus response was greater (P < 0.02) for +PG cows (76.92 ± 5.84%) than for control cows (54.17 ± 7.19%). These results indicate that, PGF2α administration at CIDR insertion and removal in a7-d CO-Synch + CIDR protocol for a Split-time AI program improved estrus response. However, pregnancy rates were lower and may have been influenced by the timing modification of FTAI to the Split-time AI program implemented. [ABSTRACT FROM AUTHOR]