Oxidative and Mitochondrial Status of Vitrified Equine In Vitro Matured Oocytes Using Temperature-Specific Equilibration Protocols.

Cryopreservation of equine in vitro matured (IVM) oocytes remains a major challenge in assisted reproduction due to their high susceptibility to cryoinjury, including oxidative stress and mitochondrial dysfunction. The aim of this study was to evaluate the physiological status of vitrified/warmed equine IVM oocytes following vitrification using two temperature-specific equilibration protocols by assessing reactive oxygen species (ROS), intracellular glutathione (GSH) content and mitochondrial oxidative activity and distribution patterns. Oocytes were vitrified after 28 h of IVM either at 25°C (in VIT25) or at 38.5°C (in VIT38.5) and cultured for an additional 2 h after warming. No significant differences were detected among groups in ROS levels, GSH content, mitochondrial oxidative activity or distribution patterns (p > 0.05). These results indicate that the vitrification protocols evaluated did not induce detectable alterations in redox balance or mitochondrial function in equine IVM oocytes. This suggests that vitrified/warmed oocytes may maintain characteristics compatible with fertilisation and subsequent embryonic development, although their developmental competence was not directly evaluated and warrants further investigation.