Pregnancies after in-vitro fertilization of cow follicular oocytes, their incubation in rabbit oviduct and their transfer to the cow uterus.

Cow embryos fertilized in vitro (1-8-cell) (n = 113) were transferred surgically to the ligated oviduct of pseudopregnant female rabbits (31 +/- 4 h after 75 i.u. hCG). Rabbits were killed 99 +/- 5 h later and 67 embryos were recovered: 45 (67%) had cleaved at least once, 15 had reached the morula stage and 2 blastocysts were obtained. Transfer of cleaved embryos (2-8-cell) led to a high recovery rate (84%) compared to 39% for one-cell embryos. Of the embryos incubated for more than 99 h in the rabbit oviduct, 41% were at the morula stage. Embryos incubated in vivo (n = 21) (8-cell to blastocyst) were transferred to the uterus of 14 synchronized recipient heifers by a surgical (N = 5) or a non-surgical (N = 9) procedure: 6 pregnancies resulted (4 from the non-surgical procedures). In addition, 27 (2-8-cell) cow embryos developed in vitro were transferred to the oviduct of synchronized heifers by a paralumbar surgical approach on a standing animal, but no pregnancies resulted. It is therefore concluded that (1) the rabbit oviduct can be used to obtain cow eggs at an embryonic stage sufficiently advanced to permit transfer to the uterus of a synchronized recipient; and (2) the pregnancy rate after in-vitro fertilization and incubation in the rabbit oviduct are similar to results with fertilization in vivo.