Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 17, 1999
Publication Date: N/A
Interpretive Summary: Cow embryos can be grown in the laboratory for 8 to 9 days before they must be transferred to a cow. If cow embryos would develop in a less expensive host than the cow, it would be easier and cheaper to conduct studies on pre-implantation embryos. This stage of development is critical to understand because it is a stage of high losses for reproductive efficiency. In the present study, cow embryos grown in the laboratory were transferred into the uteri of sheep. The embryos developed into stages appropriate for the study of the pre-implantation period. The finding of this study will be useful to scientists trying to understand this critical stage in development of the cow embryo.
In vitro matured, fertilized and cultured (IVP) cow embryos were transferred to uteri of sheep on day 7 or 9 of the estrous cycle and collected on day 14 or 15 to determine if the bovine blastocysts would elongate and form an embryonic disk. In trials 1 and 2, 37 of 55 and 48 of 70 recovered embryos developed to the spherical or elongated blastocyst stage and most had embryonic disks. In trial 3, 75% of 44 recovered embryos had elongated. Transfer of 4-cell bovine embryos to the oviduct of sheep at day 3 resulted in a lower recovery than for transfer of blastocysts at day 7 when embryos were recovered at day 14. However, the fraction of the embryos containing embryonic disks was greater for the embryos transferred at the 4-cell stage (81%) than for embryos transferred as blastocysts. The size distribution of recovered embryos was similar among embryos transferred at the 4-cell stage, super-ovulated bovine embryos, and bovine IVMFC embryos transferred at the blastocyst stage to cows and recovered on day 14. The transfer of bovine blastocysts to the sheep did not result in prolongation of the sheep's estrous cycle. Extension of the sheep estrous cycle by administration of a progesterone releasing intravaginal device allowed bovine embryos to elongate extensively and to become fibrous. Transfer of bovine embryos to the reproductive tract of the sheep allows some embryos to develop normally to uterine stages and may be a useful tool for studying critical stages of embryo development and the developmental capacity of experimental embryos.