Viability of OPS Vitrified Sheep Embryos After Direct Transfer

Abstract

The aim of this study was to evaluate the viability in the effect of open pulled straw (OPS) vitrification procedure of sheep embryos after direct transference. Embryos were produced in vivo and cryopreserved in slow freezing or OPS vitrification. The survival rates of cryopreserved embryos were compared to non-frozen standard pattern. In a first set of experiments, embryos at morula and blastocyst stages were dived in ethylene glycol (1.5 M) and frozen in an automatic freezer. After being thawed, they were directly or indirectly transferred to ewes recipient. A second group of embryos were drawn into OPS and plunged into liquid nitrogen after being exposed at room temperature for 1 min and 45 s in 10% EG plus 10% dimethyl sulphoxide (DMSO), then again for 30 s in 20% EG + 20% DMSO + 0.5 M sucrose. After being warmed, embryos were also directly transferred using a French mini straw as the catheter for the transplantation process or after in vitro dilution of cryoprotectants (two-step-process). No significant difference was observed among fresh, frozen or vitrified embryos on pregnancy rate (50.0%, 38.6% and 55.8%). However, when we evaluated only the direct transference, the pregnancy rate of OPS vitrified embryos was higher than that of frozen embryos (57.1% vs 34.8%) (p = 0.07). In addition, vitrified morulae had a higher pregnancy rate than the one with frozen embryos (64.0% vs 38.9%) (p = 0.07). Finally, our results indicate that OPS vitrification technique in association with direct transference improves the viability of sheep embryos with potential applications to field conditions.

Pregnancy rate after fixed‐time transfer of cryopreserved embryos collected by non‐surgical route in Lacaune sheep

“…Similar pregnancy rates were obtained in the current study on SF embryos (39.4%) as those achieved in a previous study in which embryos were surgically recovered (34.8%; Green, Santos, Sicherle, Landim‐Alvarenga, & Bicudo, ). Establishment of pregnancy in ruminants depends on optimal interaction between the developing embryo‐conceptus and the maternal uterine environment (Randi et al, ).…”

Cryopreservation of Sheep Produced Embryos – Current and Future Perspectives

“…However, some authors argue that morphological evaluation of thawed embryos is not accurate and the use of direct transfer of embryos can result in an improvement of 7-8% in offspring born [9]. Also, Green et al [169] found that direct transfer improves the viability of transferred vitrified sheep embryos maybe because the time elongation from warming to transfer has a detrimental effect on subsequent embryo viability. This fact could suggest that embryo evaluation after embryo warming is dispensable as predictive of success.…”

“…Green et al [169] reported higher pregnancy rates when using vitrification by OPS and direct transfer, thus enhancing the field application of this technique. Nevertheless, these good results with OPS vitrification cannot avoid the reduced cryotolerance of IVP embryos.…”

“…Regardless of the method used for embryo cryopreservation, some researchers [1,14,169] obtained promising results after direct transfer of vitrified sheep embryos for field use. These authors reported that the interval between thawing/warming and transfer has a great influence on embryo subsequent viability and valorize the use of direct transfer to spread this technique in field conditions.…”

Open pulled straw vitrification and slow freezing of sheep IVF embryos using different cryoprotectants

“…Although successful vitrification of in vivo-derived sheep embryos using straws (Baril et al 2001), OPS (Green et al 2009) and plastic micropipette tips (Cryo-tips; Gibbons et al 2011) has been achieved, the effect of varying concentrations of different cryoprotectants has not been studied extensively on cryosensitive in vitro-produced embryos. The main objective of the present study was to compare the effects of slow freezing and OPS vitrification protocols for cryopreservation of IVF sheep embryos and their viability using variable concentrations of permeable cryoprotectants.…”