Production and lambing rate of blastocysts derived from in vitro matured oocytes after gonadotropin treatment of prepubertal ewes

The aim of this study was to evaluate the effect of gonadotropin treatment on thein vitromaturation, blastocyst production, and developmental potential to term of oocytes collected from Sardinian neonatal and prepubertal ewes at 4 to 6 wk of age. Cumulus-oocyte complexes were recovered at 24 h after withdrawal of a 1/6th size progestagenated pessary from the donors, of which each received 120 IU FSH/LH and 400 IU PMSG in a single dose 36 h before sponge removal. Treated donors produced a greater ( P < .01) number of oocytes per animal (86.2 ± 7.9) compared with slaughterhouse (untreated) prepubertal ewes (55.5 ± 6.1) of the same age or with treated neonatal ewes (6.1 ± 0.7) 10 d old. During oocyte maturation, there were no differences in the percentage of germinal vesicle break-down (78.08 vs 74.24), metaphase I (89.13 vs 87.18), and metaphase II (77.91 vs 76.38) when evaluated after 8, 14, and 24 h of maturation, respectively, between oocytes from treated and slaughterhouse (untreated) prepubertal ewes. The embryo cleavage (71.1 vs 73.7) and blastocyst rates (22.2 vs 19.8) were similar in the treated and the untreated prepubertal ewes after transfer ofin vitromatured oocytes into ligated oviducts of temporary recipients. Thein vitroviability rates of vitrified blastocysts (81.2 vs 76.9) and thein vivosurvival rates (46.1 vs 50.0) of embryos derived fromin vitromatured andin vivofertilized oocytes showed no difference. The data suggest that gonadotropin treatment increases oocyte production per animal but has no effect on oocyte quality because embryo production and lambing rates of blastocysts derived fromin vitro maturedoocytes were not markedly different from those derived from untreated prepubertal ewes of the same age.