Growth retardation of inner cell mass cells in polyspermic porcine embryosproduced in vitro

The in vitro viability of polyspermic pig eggs was investigated. immature o ocytes were matured and fertilized in vitro. Approximately 10 h after insem ination, the eggs were centrifuged at 12 000 x g for 10 min and individuall y classified into two (2PN)- and poly-pronuclear (PPN, 3 or 4 pronuclei) eg gs, The classified eggs were cultured in vitro or in vivo. Nuclei numbers o f inner cell mass (ICM) and trophectoderm (TE) were compared between 2PN- a nd PPN-derived blastocysts. The frequency of development in vitro of 2PN an d PPN eggs to the blastocyst stage was 53.6% and 10.7%, respectively. The m ean number (8.2 +/- 0.7, n = 48) of ICM nuclei of 2PN-derived blastocysts w as higher than that (4.2 +/- 0.8, n = 37) of PPN-derived blastocysts (p < 0 .001), whereas there was no difference (p > 0.05) in mean numbers of total (46.7 +/- 3.4 vs. 39.9 +/- 3.9) and TE nuclei (38.5 +/- 2.9 vs. 35.7 +/- 3. 3) between the two groups. Development of 2PN and PPN eggs cultured in vivo to the blastocyst stage was 33.3% and 27.4%, respectively. The numbers of ICM and TE nuclei of these embryos cultured in vivo showed a pattern simila r to that for the in vitro-produced blastocysts. Additionally, fetuses were obtained on Day 21 from both the 2PN and the PPN groups. This suggests tha t polyspermic pig embryos develop to the blastocyst stage and beyond, altho ugh showing a smaller ICM cell number as compared to normal embryos.