Development of large and small blastomeres from 2‐cell embryos produced in vitro in pigs

Abstract

In the present study, we examined the development to blastocysts of large and small blastomeres from unevenly cleaved 2-cell embryos (uneven 2-cell embryos) in pigs. Proportion of blastocysts derived from large blastomeres (52.8 ± 6.4%) was significantly higher (P<0.05) compared with small ones (32.1 ± 4.6%). However, there were no differences in total cell number, inner cell mass (ICM) cell number and ICM/total cells ratio between them. Of 53 sister blastomere pairs in the same embryos examined there were 12 pairs (22.6%) in which both blastomeres developed to blastocysts, 16 pairs (30.2%) in which only large blastomeres developed to blastocysts, and five pairs (9.4%) in which only small blastomeres developed to blastocysts. Relative total amount of active mitochondria in small blastomeres were lower (P<0.05) than that of large blastomeres and blastomeres from evenly cleaved 2-cell embryos. However, there was no difference in relative density of active mitochondria in these three types of blastomeres. In conclusion, blastocysts derived from small and large blastomeres in uneven 2-cell embryos had comparable quality in terms of cell number, ICM number, ICM/total cell ratio and distribution of active mitochondria. The results suggest that these blastomeres may contribute multiple offspring production in pigs.