In vitro assessment of the viability of sheep zygotes after pronuclear microinjection

Microinjected sheep zygotes were cultured in synthetic oviduct fluid medium (SOFM) for either 1 or 3 days and their subsequent developmental capacity was compared with that of microinjected zygotes cultured in vivo. Two experiments were carried out, using zygotes microinjected with one of three gene constructs containing the CysE and CysM genes from Salmonella typhimurium. In Experiment 1, microinjected zygotes were allocated to one of three treatments: (1) immediate transfer to recipient ewes (in vivo culture) followed by recollection 1 or 3 days later and subsequent transfer of viable embryos to other recipient ewes, (2) culture in SOFM (in vitro culture) for either 1 or 3 days before transfer to recipient ewes, and (3) immediate transfer to recipient ewes without subsequent interference. Recipient ewes were slaughtered on Day 14 of pregnancy and the number of elongated conceptuses determined. Although fewer zygotes failed to divide during in vitro culture than during in vivo culture, there were, overall, no significant differences between treatments in the percentage of zygotes that developed into elongated conceptuses (32.6-50.0%). In Experiment 2, microinjected zygotes were transferred immediately to recipient ewes or cultured in vitro for either 1 or 3 days before transfer. The number of fetuses per ewe on Day 50 of pregnancy and the number of lambs delivered per ewe were recorded. Neither the percentage of recipient ewes that became pregnant (overall 114/166, 68.7%) nor the percentage of zygotes that developed into lambs (overall 186/803, 23.2%) was significantly influenced by the culture treatment or by the gene construct microinjected.(ABSTRACT TRUNCATED AT 250 WORDS)