Timing of in vivo maturation of equine preovulatory oocytes and competence for in vitro maturation of immature oocytes collected simultaneously.

This study focuses on understanding the timing for maturation of preovulatory oocytes in horses and checking for the in vitro maturation capability of immature oocytes collected at the same time.

Objectives of the Research

• The research aimed at understanding the development and maturation of cumulus complex and nuclear maturation in oocytes that were recovered from preovulatory follicles after inducing ovulation.
• Another objective of the research was to analyse the capability of in vitro maturation of oocytes gathered from smaller, non-preovulatory follicles, and to see if the size of these follicles played any role in their maturation.

Methods Used in the Research

• The researchers punctured all follicles that were 5mm or more in pony mares at different times such as 0, 6, 12, 24, and 35 hours after injecting LH to induce ovulation.

Findings of the Research

• Of the 55 preovulatory follicles, the research found that 64% of oocytes were recoverable. For 32 subordinate follicles, the recovery rate was 22%, and for 227 small follicles, it was 52%.
• Cumulus expansion in the preovulatory oocytes was seen to have occurred 12h post LH treatment. The metaphase I and II components of nuclear maturation were completed by 24h and 35h post LH injection respectively.
• In the case of non-preovulatory follicles, the research found an increase in atresia and oocyte competence for in vitro nuclear maturation correspondingly with the increase in the size of the follicles.

Conclusions Drawn from the Research

• The research concluded that the timing of in vivo maturation of equine preovulatory oocytes is critical to their development. Further, the in vitro maturation competence of oocytes varies based on the size of the non-preovulatory follicles they are recovered from.