Nine phenotypically normal gilts were slaughtered on the 25th day following coitus, and the embryos were harvested and cultured for karyotypic analysis. A total of 76 embryos were recovered, 8 of which were dead and in various stages of degeneration. The mean ovulation rate, based on a corpora lutea count, was 11.8 ± 0.6. Prenatal death loss, based on the ratio of embryos harvested to corpora lutea count, was estimated at 35.8 %. The diploid number of 38 chromosomes was found in 90.2 % of 797 cells counted. Karyotypic analyses revealed only one abnormal embryo, which was monosomic for pair 16. However, lethal chromosome combinations could not be ruled out as the cause of cell death in the eight dead embryos. If chromosomal abnormalities are relatively constant in nature, these results would indicate that most abnormal embryos rarely survive implantation