Evaluation of equine oocyte developmental competence using polarized light microscopy

Area of Science:

• Veterinary Reproduction
• Oocyte Biology
• Microscopy Techniques

Background:

• Assessing equine oocyte quality is crucial for reproductive technologies.
• Traditional methods rely on subjective morphological evaluation.
• Objective techniques are needed to complement current assessments.

Purpose of the Study:

• To evaluate the utility of polarized light microscopy (PLM) for assessing in vitro-matured equine oocytes.
• To compare PLM findings with classic light microscopy (LM) and parthenogenetic activation outcomes.
• To determine if PLM can objectively distinguish mature from immature and activated from non-activated oocytes.

Main Methods:

• Equine cumulus-oocyte complexes (COCs) underwent in vitro maturation (IVM) for 24, 36, or 45 hours.
• 36-hour matured oocytes were analyzed using classic light microscopy (LM) and polarized light microscopy (PLM).
• Mature oocytes were parthenogenetically activated to assess quality and meiotic competence, with zona pellucida (ZP) properties analyzed by PLM.

Main Results:

• The 36-hour IVM protocol yielded a 47.01% maturation rate.
• Immature oocytes showed significantly increased ZP thickness and inner layer (IL-ZP) retardance compared to mature oocytes.
• Parthenogenetically activated oocytes exhibited significantly increased IL-ZP area and thickness compared to non-activated oocytes.

Conclusions:

• A 36-hour IVM protocol is effective for equine oocytes.
• PLM provides an objective method to differentiate mature from immature equine oocytes.
• PLM can also distinguish between activated and non-activated oocytes, aiding in quality assessment.