Effects of a GnRH antagonist on antral follicular development and ovarian hemodynamics in cycling ewes.

Sixteen multiparous Santa Inês ewes underwent transrectal ovarian ultrasonography from days 6 to 17 (D6-17; D0 = ovulation). On D6, ewes received a single subcutaneous injection of Firmagon® at a low dose (LD; n = 5; 215 µg/kg body weight [b.w.]) or a high dose (HD; n = 6; 235 µg/kg b.w.); controls (C; n = 5) received saline. Ovulations were detected in 100% of controls, but only in 20% of LD and 17% of HD animals. Mean daily numbers of large antral follicles (> 4.49 mm) decreased (P < 0.05) between D6 and D7 in HD group. Compared with controls, LD ewes had higher (P < 0.05) ovarian artery pulsatility index (PI; D16-17) and resistive index (RI; D17), but lower flow-propagation velocity (FPV; D17), whereas HD ewes exhibited higher PI (D15) and RI (D17), along with lower FPV (D8 and D15) and end-diastolic velocity (D17). Firmagon® treatment was associated with a reduced number of large antral follicles and alterations in ovarian blood perfusion.