Role of the embryonic vesicle and progesterone in embryonic loss in mares.

This research study examines the role the embryonic vesicle and progesterone play in embryonic loss in mares. It finds a correlation between size and positioning of the embryonic vesicle, as well as progesterone concentration, and early pregnancy loss.

Study Setup

• The study compared circumstances of spontaneous embryonic loss in 21 mares with those of 52 mares that maintained pregnancy.
• The mares with embryonic loss were retrospectively divided into three groups based on day of loss and length of the interovulatory interval – Group 1 experienced loss on or before day 20 with interovulatory interval 30 days; and Group 3 experienced loss after day 20 with interovulatory interval >30 days.
• Ovulation was considered as day 0 for measuring purposes.

Key Findings

• The mean diameter of the embryonic vesicle was recorded to be smaller on days 12-18 in Group 1 mares compared to the mares that maintained pregnancy.
• Despite size variations, the average growth rates of embryonic vesicles remained comparable across the pregnancy-continued group and all three loss groups.
• Frequent location of vesicles in the uterine body on day 13 in Group 1 seemed to be related to the larger proportion of small vesicles. On day 18, an increased rate of fixation failure was suspected as the reason.
• Luteal regression seemed to occur as expected in 77% of the mares that experienced loss on or before day 20.
• The researchers observed a lower concentration of progesterone on days 12, 15, and 18 and a decrease in diameter of the corpus luteum on days 15 and 18 in mares of group 1, indicating that luteolysis was not prevented by the embryonic vesicle in this group.

Conclusion

• The study’s findings suggest that smaller size of the embryonic vesicle, its location in the uterine body, and lower progesterone concentrations correlate with early pregnancy loss in mares.