The influence of various in vitro procedures on embryo survival and the production of normal offspring was investigated in sheep. Zygotes produced from in vitro matured (IVM) and fertilized (IVF) oocytes derived from slaughtered Merino ewes were allocated to three culture treatments for 6.5 days. Two groups were cultured in vitro in the absence or presence of oviduct epithelial cells while the third group was cultured in vivo in the oviducts of synchronized ewes. A fourth group of zygotes obtained from superovulated Merino ewes was also cultured in vivo and served as controls. After culture, IVM–IVF morulae and blastocysts, and control embryos were transferred to final recipient ewes. Pregnancy was diagnosed at day 50 of gestation by ultrasonography and pregnancies were allowed to go to term. The survival to term of IVM–IVF zygotes cultured in vitro was reduced compared with both in vivo cultured IVM–IVF zygotes and control zygotes 25–35% versus 51–60%, respectively, P < 0.05). Day 6.5 IVM–IVF morulae had a lower survival rate than did control morulae regardless of culture treatment (P < 0.05), while survival rates of day 6.5 IVM–IVF blastocysts cultured in vivo did not differ from those of control blastocysts (P > 0.1). Both the gestation period and birth weight of IVM–IVF lambs were increased when compared with controls, the former significantly in all groups (154.0–154.9 days versus 150.6 days; P < 0.01), while the latter increase was on the borderline of significance (4·5–4·8 kg versus 4.0 kg; 0.01 ≤ P ≤ 0.1, respectively) and dependent on the prolongation of the gestation period. It is concluded that in vitro maturation and fertilization compromise subsequent embryonic and fetal development in sheep irrespective of the subsequent in vivo or in vitro culture treatment. Subjecting IVM–IVF zygotes to in vivo culture for 6.5 days minimizes only some of these effects, thus leading to the aberrant production of some offspring.
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