Effects of GnRH and Prostaglandin Combined with a Short Progestin Regimen on the Synchrony of Estrus and Ovulation in Ewes During the Breeding Season

Two trials were conducted to quantify the effects of GnRH and prostaglandin in conjunction with a 7-d CIDR on estrus and on pregnancy rate in comparison with a traditional synchronization protocol. In trial 1, ewes (n=12) were randomly allotted to one of three treatments: CIDR (7 d) with administration of GnRH (Cystorelin®, 50μg, im) at CIDR insertion and PGF2α (Lutalyse®, 20 mg, im) on d 6.5 (GnRH1); the GnRH1 protocol with a second injection of GnRH 30 h after CIDR removal (GnRH2); and CIDR (11 d) with administration of PGF2α at CIDR insertion and PMSG (400 iu) at CIDR removal (PMSG). A blood sample was obtained every 2 h for 42 h after CIDR removal for serum LH analysis. On d 8 after CIDR removal, blood samples were obtained at 12 h intervals for 36 h for serum P4 analysis. One ewe in the GnRH1 group did not retain the CIDR device and was excluded from the analysis. Mean LH concentration did not differ (P = 0.48) among groups. Time and time x treatment affected (P 0.05) among the groups. Marking frequency was 92 percent, 75 percent, and 88 percent for GnRH1, GnRH2, and PMSG groups, respectively. Mean interval to estrus was shorter (P < 0.05) for the GnRH2 than for the PMSG group and tended to be reduced (P < 0.10) compared with the GnRH1 group. Pregnancy rate differed (P < 0.05) among treatments (79 percent, 58 percent and 38 percent for GnRH1, GnRH2, and PMSG groups, respectively). These results indicate that synchrony of estrus and pregnancy rate to natural service can be increased in response to a CIDR protocol when combined with administration of GnRH rather than PMSG