Vitrification of immature equine oocytes using synthetic ice blockers: ultrastructural injuries and maturation rates

Low maturation rates have been obtained after vitrification of immature equine oocytes [Tharasanit et al., Reproduction 2006;132:759-69]. Although oocyte cryopreservation technique is critical for equine assisted reproduction programs, this is still an inefficient process, in part, to an inadequate oocyte competence post-thawing which can be compromised by changes resulting from cold shock [Chen et al., Mol Cell Endocrinol 2003;202:101-7]. Thus, investigations are needed for a better understanding of developmental competence of equine oocytes after vitrification. Low concentration of synthetic ice blockers (SIB) inhibits ice crystal formation [Wowk et al., Cryobiology 2000;40:228-36], and has recently been used for vitrification of equine oocytes [de Leon et al., Theriogenology 2012;77:21-27]. The objectives of this study were to identify ultrastructural morphological injuries and maturation rates in equine oocytes submitted to vitrification solutions (VS) with SIB during different exposure times. In Experiment 1, cumulus-oocyte complexes (COCs) were allocated to treatments: (a) Fresh COCs fixed after selection (Control; n1⁄4 10); (b) COCs exposed to VS-1 (1.4 M DMSO + 1.8 M EG + 1% SIB) for 3 min and VS-2 (2.8 M DMSO + 3.6 M EG + 0.6 M Sucrose + 1% SIB) for 1 min (Eq-long; n1⁄4 10); and (c) COCs exposed to VS-1 for 1.5 min and VS-2 for 30 s (Eq-short; n 1⁄4 10). COCs were vitrified using open-