Intra uterine survival and growth of Wistar and Wistar × Brown Norway rat embryos

Embryos of the Wistar strain and its F1 cross (Wistar females mated with Brown Norway males) of rats were transferred nonsurgically to 48 Wistar, 17 F1 cross and 20 Wistar-Imamichi recipients. The two types of embryos were transferred together to each recipient to compare the viability of the embryos. Pregnancy rate was 78.8% (6785). The survival rate of fetuses to term was 11.5% (20174) and 25.1% (42168) for the Wistar and F1 embryos, respectively. Placental weight differed significantly (P<0.05) between embryo types and among recipient types while fetus weight differed (P<0.01) only among recipient types, with a significant interaction between recipient and embryo types (P<0.01). It was concluded that the F1 embryos (Wistar × Brown Norway) were twice as viable as Wistar embryos under the conditions provided.