Overnight holding aids in selection of developmentally competent equine oocytes.

The research investigates how different holding and in vitro maturation (IVM) times affect the development of equine (horse) oocytes, or egg cells. The study indicates that leaving immature oocytes in a holding phase overnight before a standard IVM period may improve cell cleavage and embryo development.

Objective of the Research

• The goal of this study was to measure the effect of modified In Vitro Maturation (IVM) timings and an extended period before fertilization, including periods of holding, on the developmental competence of equine oocytes.
• This is important because demand for in vitro produced equine embryos has been rising, so optimizing the process is essential.

Methodology

• The researchers used oocytes collected from ovaries obtained from an abattoir.
• These oocytes were divided into 4 groups based on the duration of holding times and IVM processes. They were designated H0/24, H8/36, H20/24, and H0/44.
• After maturing to the MII phase, these oocytes were fertilized using Intracytoplasmic Sperm Injection (ICSI) and cultured for 10 days.

Findings

• The rate of oocyte degeneration was significantly higher (54.5%) for the H20/24 group than the others, suggesting this holding period and IVM timing may be less successful.
• Oocyte cleavage, a vital process in successful embryo development, was highest (70%) in the H20/24 group, followed by H0/44 (63%), H8/36 (54%), and H0/24 (45%).
• Blastocysts development per oocyte did not differ among the groups.
• The percentage of injected oocytes reaching the blastocyst stage was highest for the H20/24 group (20%) compared to H0/24 and H0/44, both with 7%, but comparable to H8/36 (12%).
• A higher blastocyst rate was observed for cleaved oocytes in the H20/24 group (28%) than the H0/44 group (11%).

Conclusion

• The study concludes that an overnight holding phase followed by a standard IVM period may result in pre-selection of more competent oocytes, as evidenced by higher cleavage and embryo development rates after Intracytoplasmic Sperm Injection (ICSI).