Ultrastructure of cryopreserved horse embryos.

Embryos were recovered non-surgically at about Day 6 after ovulation from 15 Quarter horse-type mares and were evaluated for morphological changes which may occur because of exposure to the cryoprotectant and/or cryopreservation. Electron microscopy was used to elucidate the fine structure of intracellular organelles which, if damaged, could cause cellular death. The horse embryo does not totally re-expand in the 10% glycerol freezing medium, nor will it completely re-expand in the isotonic holding medium following glycerol removal whether or not the embryo has been frozen. Embryos in this study were frozen by the same protocol which had resulted in a 30% pregnancy rate for similarly frozen embryos. Junctional complexes between trophoblast cells, as well as the plasma and nuclear membranes of trophoblast and inner cell mass (ICM) cells, were intact after treatment in all embryos. Changes in lipid droplets and some mitochondrial degeneration were observed in the ICM cells of the glycerol-treated embryos. The change in the lipid was not observed in the frozen-thawed embryos, but mitochondrial changes were evident in the trophoblast and ICM cells, with the most extensive mitochondrial damage in the ICM cells.