Exogenous progestogen does not affect first-wave follicle populations and oocyte quality during ovarian stimulation with FSH in sheep

Abstract The effect of short-term administration of medroxyprogesterone acetate (MPA) or natural progesterone (P 4 ) during ovarian stimulation with FSH on oocyte recovery was investigated in Santa Ines ewes. Ewes were treated with intravaginal sponge containing MPA for 6 days; GnRH was applied 36 h after sponge removal and FSH in three injections (40 mg, 24 mg, and 16 mg, respectively) every 12 h after (D0, approximate ovulation time). At the first FSH dose, the ewes received either a new MPA sponge (n=10) or a CIDR impregnated with P 4 (n=10) or did not receive any device (n=10). Ovarian dynamics were assessed every 12 h by transrectal ultrasonography from D-3 to D2. Oocytes were recovered by laparoscopic ovum pick up (LOPU) on D2 and graded by morphological quality. The number of small, medium and large follicles at D0 and D2 (ultrasound exams); number of both follicles aspirated and oocytes recovered at LOPU, recovery rate, and oocyte grade did not differ ( P >0.05) among treatments. Thus, the short-term use of MPA or P 4 during ovarian stimulation did not affect the first-wave follicle population or morphological quality of oocytes. We would suggest that, in this protocol, the use of exogenous progestin is unnecessary.