Viability of in vitro produced cattle embryos.

Abstract

Embryo transfer is being increasingly used in the cattle industry. As well as direct embryo transfers, many embryo-based biotechnologies have the potential to improve cattle production efficiency through enhanced breeding strategies, by facilitating the introduction of desirable traits such as disease resistance and through the production of desirable medical or pharmaceutical products in the milk. These biotechnologies are, however, dependent on a supply of viable in vitro produced (IVP) embryos. While the in vitro fertilization rate is high (80%) in cattle, only about 30 transferable embryos, or blastocysts, are produced from every 100 fertilized oocytes. A major factor affecting the viability of IVP embryos is their failure, in a high proportion of cases, to undergo normal development to the blastocyst stage in the manner of in vivo embryos. The major problem relates to a failure of the cells of IVP embryos to form a compact cell mass when they are 5 - 6 days old. This ultimately leads to developmental problems and compromised viability. Cell compaction is recognized as a critical event in early embryo development and has been associated with marked changes in protein synthesis and phosphorylation in the embryos of some species. This report is the first, to our knowledge, to describe the rate and pattern of protein synthesis and phosphorylation before, during and after compaction in both in vivo and in IVP cattle embryos. The main results are summarised below.