In vitro fertilization of in vitro-matured equine oocytes: effect of maturation medium, duration of maturation, and sperm calcium ionophore treatment, and comparison with rates of fertilization in vivo after oviductal transfer.

The research investigated the impact of various oocyte and sperm treatments on horse in vitro fertilization (IVF), and the ability of in vitro-matured horse oocytes to be fertilized in vivo. It found that the environment in which oocyte matures significantly affects fertilization rates but duration of maturation and sperm treatment have no effect.

Study Design and Experiments

• Three different experiments were conducted to understand how oocyte and sperm treatments influence IVF in horses. The ultimate goal was to see whether in vitro-matured horse oocytes can be fertilized in vivo.
• The study compared two durations of oocyte maturation: 24 hours and 42 hours. Two concentrations of calcium ionophore during sperm capacitation were also compared: 3 microM and 7.14 microM. The rate of IVF was not significantly affected by either of these variables.

Follicular Fluid versus Maturation Medium

• Oocytes that matured in 100% follicular fluid had a significantly higher fertilization rate (13 to 24%) compared to those matured in either a maturation medium or in 20% follicular fluid (0 to 12%).
• However, beyond fertilization, the study also found a significant difference in embryonic development between the two maturation environments. A significantly higher percentage of oocytes matured in maturation medium cleaved into two or more cells (63%) than those matured in follicular fluid (22%).

Sperm Treatment and In Vivo Fertilization

• Three sperm treatments using 7.14 microM calcium ionophore were applied. There was no significant difference in fertilization rate among these treatments (12 to 21%).
• The study also included an in vivo verification experiment, where in vitro-matured oocytes were transferred to the oviducts of inseminated mares. Of the oocytes recovered 40-44 hours after the procedure, 77% showed normal fertilization (displaying 2 pronuclei to normal cleavage).

Conclusion

• The research concluded that horse oocytes matured in vitro are capable of being fertilized at high rates, given the right environment.
• Natural maturation in follicular fluid boosted the in vitro fertilization rate. However, this appears to limit embryo development post-fertilization in a natural in vivo setting.
• The paper highlights the need for additional research to determine the best environment for sperm capacitation and IVF in horses.