The effect of sucrose in the thawing solution on the morphology and mobility of frozen equine embryos

Summary Seventy‐five embryos were collected 6 days after ovulation. Sixty embryos were frozen in straws using glycerol as the cryoprotectant in an automatic freezer. In Experiment 1 the freezing and thawing media were supplemented with 1.3 g/l PVP; in Experiment 2 the supplement was 5% FCS. The embryos were thawed for 30 s at +37°C in a waterbath. In Experiment 1 glycerol was removed from 10 embryos in 6 steps. In 10 other embryos, glycerol and sucrose were both removed from the medium in 6 steps. After glycerol and sucrose removal, the embryos were stained with 4′,6′‐diamidino‐2‐phenylindole (DAPI) to count the percentage of dead cells. Fluorescent rate (FR) was defined as a ratio of fluorescent area versus total area. Mean (± s.d.) FR in this experiment was significantly lower (P < 0.01) in embryos thawed with sucrose (0.28 ± 0.13) than in embryos thawed with glycerol alone (0.53 ± 0.25). In Experiment 2, 40 embryos were frozen and glycerol, with or without sucrose, was removed after thawing as for Experiment 1. Ten embryos in both groups were stained with DAPI. All the frozen‐thawed embryos were transferred nonsurgically to recipient mares. Fourteen fresh embryos were transferred as controls, 7 of which were stained with DAPI before transfer. There was no difference in pregnancy rates between DAPI‐stained versus nonstained embryos, indicating that the staining process had no negative effects on embryonic survival. Insufficient embryos were transferred to be able to demonstrate any difference in pregnancy rates between embryos thawed with or without sucrose in the medium.