The Correlation of Endogenous Progesterone Concentration in Diestrus on Early Pregnancy Rate in Thoroughbred Mares.
Authors: Hollinshead Fiona Kate, Mehegan Mary Kate, Gunn Allan, Nett Terry, Bruemmer Jason Edward, Hanlon David William
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Establishing whether early progesterone levels predict pregnancy success in mares has significant implications for stud farm management and intervention strategies. Researchers measured serum progesterone concentrations five days post-ovulation in 275 Thoroughbred mares across five New Zealand studs, then confirmed pregnancy status via ultrasound at day 14 of gestation. Pregnant mares demonstrated statistically higher progesterone levels (6.4 ± 3.0 ng/ml) compared with non-pregnant mares (5.5 ± 3.3 ng/ml; P = 0.02), confirming a positive association between early diestral progesterone and early pregnancy establishment. However, the modest difference and overlapping ranges meant no definitive threshold could be identified to reliably predict individual pregnancy outcomes, and whilst mare age inversely affected pregnancy rate, it did not influence progesterone concentration itself. For practitioners, these findings suggest that whilst progesterone measurement at day 5 may have limited diagnostic utility for individual cases, investigation of exogenous progestin supplementation in naturally bred mares—particularly older animals—warrants further research as a potential strategy to improve conception rates on commercial studs.
Read the full abstract on PubMed
Practical Takeaways
- •Progesterone measurement at Day 5 post-ovulation may serve as a marker for pregnancy success in Thoroughbred mares, though it cannot be used as a standalone predictive tool with a defined threshold
- •Older mares have reduced pregnancy rates independent of progesterone levels, suggesting age-related factors beyond hormonal concentration affect fertility
- •Further research is needed to determine if synthetic progestogens can improve pregnancy rates in naturally bred mares as an alternative to relying on natural progesterone levels
Key Findings
- •Progesterone concentration at Day 5 post-ovulation was significantly higher in pregnant mares (6.4 ± 3.0 ng/ml) compared to non-pregnant mares (5.5 ± 3.3 ng/ml; P = 0.02)
- •Mare age showed a negative association with pregnancy rate but had no effect on progesterone concentration at Day 5
- •While higher serum progesterone at Day 5 post-ovulation was associated with higher pregnancy rates at Day 14, no predictive or definitive minimum progesterone concentration threshold could be identified