The effect of co-culture on the development of in vitro matured equine oocytes after intracytoplastic sperm injection.

The study examines the impact of different in vitro culture systems on the development of horse oocytes (eggs) after they have been artificially fertilized. The research found that co-culture systems showed better results for in vitro embryo development compared to simpler culture methods.

Objective

The primary goal of the research was to identify the most effective in vitro culture system for the development of horse embryos. This was attempted by assessing the embryonic development of horse oocytes within three different culture environments following intracytoplasmic sperm injection (ICSI).

Methodology

• Oocytes suitable for culture were collected from 55 ovaries. These were divided into two categories based on their cumulus morphology: expanded cumulus and compacted cumulus. The oocytes were then matured in vitro using TCM 199 with 10% FCS and 0.1 iu/ml FSH/LH, under specific conditions.
• Oocytes that reached metaphase II were subjected to ICSI using frozen semen. They were then placed in three different culture environments: A) TCM 199 + 10% FCS, B) on a granulosa cell monolayer, and C) SOF + MEM amino acids + 0.8% BSA, each under varying conditions.

Results

• The fertilization rate across all methods was 32%.
• The cleavage rate in Group A was 74.4%, with 18 embryos reaching 2-6 cell stages, eight reaching 8-16 cell stages, four reaching 16-32 cell stages, and two reaching >32 cell stages.
• In Group B, the cleavage rate was slightly lower at 73.5%, however, the results showcased better embryonic development with successful progression through the early cell stages and higher numbers reaching the later cell stages.
• In Group C, the cleavage rate was significantly lower than in Groups A and B. Only 39.1% of ICSI oocytes cleaved with a maximum development to the 2-6 cell stage. The majority of the remaining oocytes degenerated during culture.

Conclusion

Based on these findings, the research concluded that in vitro matured horse oocytes can be efficiently fertilized in vitro using ICSI, and co-culture systems (like Group B) are superior for supporting in vitro embryo development compared to simpler methods. Understanding the factors beneficial for in vitro embryo development provided by somatic cells can be important in optimizing the culture systems for horse embryos.