Chromosome abnormalities in secondary pig oocytes matured in vitro.

Abnormalities of chromosome segregation during in vitro maturation of oocytes cause failure of in vitro fertilization. Oocytes collected from pig ovaries after slaughter were matured in vitro (IVM) for 30-48 h. In total, 1144 secondary oocytes were studied cytogenetically. An unreduced (diploid) chromosome set was identified in 146 spreads (12.8 %). A higher proportion of diploidy was noticed in secondary oocytes matured for 40 h and longer (15.0 %) than in the groups matured for 30 and 36 h (9.0 %). Among 998 secondary oocytes with the reduced chromosome number, 612 could be analyzed in detail. Hypohaploidy (n=19-1) was identified in 22 cells (3.59 %) and a hyperhaploid (n=19+1) set of chromosomes was identified in 15 cells (2.45 %). The rate of aneuploidy, estimated by doubling the rate of hyperhaploidy was 4.9 %. It was also found that aneuploid spreads occurred more frequently in the group of oocytes matured for 40 h and longer. Small acrocentrics were mostly found as an extra chromosome in the hyperhaploid spreads. Our study indicates that to avoid an excess of chromosomally abnormal secondary oocytes, IVM duration of pig oocytes should not exceed 40 h.