EMBRYO VIABILITY, DURATION OF GESTATION AND BIRTH-WEIGHT IN SHEEP AFTER TRANSFER OF IN-VITRO MATURED AND IN-VITRO FERTILIZED ZYGOTES CULTURED IN-VITRO OR IN-VIVO

The influence of various in vitro procedures on embryo survival and th e production of normal offspring was investigated in sheep. Zygotes pr oduced from in vitro matured (IVM) and fertilized (IVF) oocytes derive d from slaughtered Merino ewes were allocated to three culture treatme nts for 6.5 days. Two groups were cultured in vitro in the absence or presence of oviduct epithelial cells while the third group was culture d in vivo in the oviducts of synchronized ewes. A fourth group of zygo tes 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. Pregna ncy was diagnosed at day 50 of gestation by ultrasonography and pregna ncies were allowed to go to term. The survival to term of IVM-IVF zygo tes cultured in vitro was reduced compared with both in vivo cultured IVM-IVF zygotes and control zygotes (25-35% versus 51-60%, respectivel y, P < 0.05). Day 6.5 IVM-IVF morulae had a lower survival rate than d id control morulae regardless of culture treatment (P < 0.05), while s urvival 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 da ys 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 less than o r equal to P less than or equal to 0.1, respectively) and dependent on the prolongation of the gestation period. It is concluded that in vit ro maturation and fertilization compromise subsequent embryonic and fe tal 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 th e aberrant production of some offspring.