eCG concentrations, luteal structures, return to cyclicity, and postabortion fertility in embryo transfer recipient mares.

The research documents the nuances of equine chorionic gonadotropin (eCG) levels, ovarian characteristics, return of cyclicity, and fertility following induced abortion in horse surrogate mothers carrying male embryos. The researchers found that these eCG levels at the time of abortion were highly inconsistent and did not strongly correlate with the count of luteal structures or the duration between abortion and the first ovulation.

Research Methodology

• The study involved 32 pregnant horses that were carrying a male fetus and were made to abort at around 65 days of gestation using a cloprostenol dose administered transcervically.
• Another group of 25 mares of equivalent gestation duration served as controls who were not made to abort.

Findings and Observations

• Post-abortion, it was noticed that the progesterone levels differed substantially between the controls and the aborted mares. However, the eCG levels did not show such a difference.
• Approximately 84.4%, or 27 out of 32, of the treated mares expelled the fetus within 48 hours of the treatment.
• The levels of eCG and the count of additional luteal structures were found to be lower in mares that were aborted in November as compared to those in January.
• Subsequent to the abortion, 6.2% of the mares entered anestrus, 37.5% ovulated normally, and 56.2% experienced 1 to 2 consecutive anovulatory cycles.
• The average duration from the abortion to the first ovulation was found to be 28.5 ± 3.3 days (with a range of 5-65 days).
• The correlation between eCG levels at the time of abortion and the time interval to the first ovulation was found to be weak (r = 0.38; P = 0.03).

Post-Abortion Fertility

• Among the mares that had aborted, 90% (18 out of 20) were reused as surrogates and became gravid after an embryo transfer. This occurred on average 57.6 ± 4.4 days post-abortion (with a range of 19-103 days) and at an eCG concentration of 0.9 ± 0.3 IU/mL (ranging between 0.1 and 3.6 IU/mL).

Conclusion

• The study concludes that the eCG levels at the time of induced abortion were quite variable and lacked a strong correlation with the number of luteal structures or the time interval from abortion to the following ovulation.