Fertility rates following the transfer of ovine embryos cryopreserved using three protocols

The aim of this study was to compare the efficiency of three cryopreservation techniques namely, controlled slow freezing, conventional vitrification and open pulled straw (OPS) vitrification, for the cryopreservation of in vivo produced Portuguese Black Merino ovine embryos. Fresh (control group) and cryopreserved embryos (3 methods) were transferred by laparoscopy to recipient ewes (2 embryos/recipient). Embryo survival rates were assessed and pregnancy diagnosis was performed by serum progesterone concentration on day 18 and by ultrasonography on day 45, and at lambing. Successful pregnancy and embryo survival rates did not differ between the fresh (73.3 and 50.0%, respectively) and cryopreserved (58.3 and 38.5%, respectively) embryos. No differences in lambing and embryo survival rates were observed between the three cryopreservation methods used (68.4 and 44.7%; 50.0 and 33.3%; 54.5 and 36.3% for controlled slow freezing, vitrification and OPS, respectively). Pregnancy rate based on serum progesterone concentration on day 18 was higher than the pregnancy diagnosed at 45 days following transfer for the cryopreserved embryos. It could be concluded that all three cryopreservation techniques were equally efficient in preserving and propagating genetic material in Portuguese Black Merino sheep.