Viability of Blastocysts and Morulae Cultured from 1-cell Stage and Transferred to Recipients in the Mouse

morulae or 4 days to blastocysts before transfer into the oviducts or uteri of recipients on the first or third day of pseudopregnancy. The proportion of pregnant animals, number of implantations and number of live fetuses on day 18 of gestation were not significantly different among the four groups tested. The proportions of live fetuses after transfer of morulae and blastocysts were 26% and 31% in the oviduct, and 37% and 36% in the uterus, respectively. The interests on parthenogenesis, cloning via homozygosity and nuclear transfer or gene transfer in mammals are now expanding. The eggs treated under the various conditions should be transferred into recipients for the final evaluation of the viability. Embryo transfer in mammals has been used in numerous studies. However, there are few reports on the viability of embryos cultured from 1-cell stage after transfer to recipients, even in the mouse in which methods for in vitro culture of early cleavage stages are well established 1-3). HOPPE and PITTS (1973)4), and KASAI et al. (1979) 5) obtained offspring in the mouse after transfer of embryos fertilized in vitro and cultured to morula or blastocyst stage. Recently, HOPPE & COMAN (1983) 6) reported that significantly fewer live fetuses were produced in the mouse when blastocysts rather than morulae (34.5%), developed from 1-cell stage, were transferred into the uteri of recipients. The present study demonstrates that the proportion of live fetuses on day 18 of gestation is not significantly different among the embryos transferred at morula or blastocyst stage, into the oviducts or uteri of recipients.