DEVELOPMENT OF IN-VITRO DERIVED BOVINE EMBRYOS FOLLOWING PRONUCLEAR TRANSPLANTATION AND IN-VITRO CULTURE

This study was designed to evaluate the survival and development of in vitro derived bovine embryos following pronuclear transplantation and in vitro embryo culture. Bovine zygotes were produced by in vitro mat uration and in vitro fertilization. Pronuclei were removed by microman ipulation and either transferred back to the same cell (Group 1) or in to a previously enucleated zygote (Group 2) by electrofusion. Microman ipulated and non-micromanipulated (Group 3, control) zygotes were co-c ultured with oviductal cells in a sealed modular chamber filled with 5 % CO2, 5% O-2 and 90% N-2 at 39 degrees C for 7-8 days. Fusion rates w ere similar for Groups 1 and 2 (90.7 and 85.1%, respectively, P > 0.05 ). The percentage of embryos that cleaved was not different for Groups 1 (82.0%), 2 (90.0%) and 3 (76.9%, P > 0.05). Also, the percentage of embryos developing to the compact morula or blastocyst stage was simi lar (25.6, 22.5 and 22.3%, respectively, for Groups 1, 2 and 3, P > 0. 05). The results of this experiment are the first to demonstrate that pronuclear transfer can be carried out successfully using bovine embry os derived from in vitro oocyte maturation and in vitro fertilization. In addition, pronuclei can be transferred from one bovine embryo to a nother and the reconstructed embryos develop to the compact morula and blastocyst stage in vitro. This technique, used in combination with o ocyte retrieval by ultrasound-guided follicular aspiration and embryo transfer, offers the potential to study cytoplasmic inheritance in cat tle directly, and to evaluate the effect of cytoplasmic inheritance on traits of economic importance.