The in vitro and in vivo developmental capacity of selected porcine monospermic zygotes

In this study, we evaluated the in vitro and in vivo developmental capacity of selected monospermic zygotes produced in vitro. Cumulus-oocyte complexes were matured in vitro and inseminated with frozen-thawed spermatozoa. Thirteen hours after insemination, presumptive zygotes were centrifuged at 15,000 × g for 20 minutes to polarize the lipids in the cytoplasm and permit the visualization of pronuclei. Then, the oocytes were individually classified as bipronuclear (2PN) or polypronuclear (three or more pronuclei, PPN). To examine embryo development, 102 selected zygotes were cultured for 7 days. There were no differences in cleavage rate (93.0% and 88.9% for 2PN and PPN zygotes, respectively). However, the blastocyst formation rate was higher (P < 0.003) in 2PN (80.7%) zygotes than in PPN (53.3%) zygotes. The control (noncentrifuged, nonselected zygotes) group showed lower (P < 0.003) cleavage rate and blastocyst formation than the 2PN and PPN zygotes. In a second experiment, 2PN zygotes and control zygotes were transferred (30 zygotes per transfer) by laparoscopy into the oviducts of recipient gilts (10 recipients per group) on the first day of standing estrus. The farrowing rates were 70% and 40% for transfers made with 2PN and control zygotes, respectively. The average number of piglets born per recipient farrowed did not differ between groups (4.9 ± 0.6 and 4.5 ± 1.2, respectively), but the efficiency (number of live piglets per total transferred embryos) was higher (P < 0.01) for 2PN zygotes than for the control group (9.3% and 4.0%, respectively). These results demonstrate the effectiveness of centrifugation for the selection of monospermic zygotes as a procedure to improve in vitro embryo production in pigs. In addition, the results indicate that the laparoscopic technique described here is a simple and effective procedure for transferring embryos into one oviduct.