Blastocyst formation rates in vivo and in vitro of in vitro-matured equine oocytes fertilized by intracytoplasmic sperm injection.

The article presents a study examining the formation rates of equine blastocysts either in vivo or in vitro using matured equine oocytes fertilized by intracytoplasmic sperm injection. The overall objective was to compare the efficiencies of viable embryo development through different methods and medium conditions.

Research Methodology

• The study began by collecting equine oocytes from ovaries sourced from a slaughterhouse. They were then matured in vitro or outside of a living organism using specialized culture conditions.
• The matured oocytes were then fertilized using a procedure known as intracytoplasmic sperm injection. This required the use of frozen-thawed stallion sperm, which was injected directly into each matured oocyte.
• To measure the development of these fertilized oocytes or zygotes in vivo, the researchers transferred the zygotes into oviducts of recipient mares. After 7.5 to 8.5 days, the mares were euthanized, and their uteri and oviducts were flushed to recover any embryos.

Results of In Vivo Development

• Out of the 132 injected zygotes that were transferred to the recipient mares, 69 (or 52%) were successfully recovered, indicating over half of the transferred zygotes were able to develop and survive in the mare’s reproductive system.
• Of these 69 recovered zygotes, 25 (or approximately 36%) had developed into blastocysts with distinguishable characteristics like a blastocoel (inner cavity) and a capsule. Blastocyst stage indicates successful embryonic development.

In vitro Development Assessment

• In addition to in vivo development, the researchers also examined in vitro development using three different culture systems or mediums.
• However, none of the zygotes cultured in a medium called Chatot, Ziomek, Bavister modified with BSA and different concentrations of glucose over time formed any blastocysts.
• The medium that yielded successful development to the blastocyst stage was the Dulbecco modified Eagle medium (DMEM)/F-12 with 10% fetal bovine serum. This medium resulted in 16% blastocyst development without coculture and 15% with a coculture of equine oviductal epithelial explants.
• The in vitro blastocyst development was significantly lower in certain mediums (2%) compared to the DMEM/F-12/BSA medium (18-20%), suggesting specific requirements for equine embryos differ from other species.

Conclusions

• The study concluded that in vitro-matured equine oocytes are competent enough to form blastocysts (36%) under optimal conditions in vivo.
• Though an in vitro culture system was identified that consistently supported blastocyst development without the need for co-culture, it only produced half the success rate of those developed in vivo.