Follicular Dynamics and Pregnancy Rates during Foal Heat in Colombian Paso Fino Mares Bred under Permanent Grazing.
Authors: Cardona-García Mauricio, Jiménez-Escobar Claudia, Ferrer María S, Maldonado-Estrada Juan G
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Foal Heat Fertility in Colombian Paso Fino Mares Follicular dynamics during foal heat vary considerably between mares and may influence breeding success, yet little is known about how tropical environments affect these physiological patterns in breeds selected for performance rather than reproduction. Researchers retrospectively analysed ovarian ultrasound records from 24 Colombian Paso Fino mares managed on permanent pasture in tropical rainforest conditions, tracking follicle development from late pregnancy through foal heat ovulation and comparing outcomes between mares that conceived (n=17) versus those that did not (n=7) following artificial insemination with semen of proven quality. Successful conception was associated with delayed first ovulation (days 11–13 postpartum versus days 7–9), larger pre-ovulatory follicles (48.6 mm versus 43.0 mm diameter), and lower uterine oedema scores at ovulation—counterintuitively, faster follicle growth rates predicted pregnancy failure rather than success. The overall conception rate of 71% when breeding at foal heat occurring in the second to third postpartum week suggests that timing of ovulation within the foal heat window significantly influences fertility outcomes, and that excessive speed of follicular maturation, particularly when accompanied by pronounced oedema, may indicate suboptimal uterine receptivity in this breed under tropical grazing systems. These findings warrant consideration when planning foal heat breeding protocols, as delayed ovulation coupled with more mature follicular and endometrial characteristics may optimise pregnancy rates in Paso Fino mares.
Read the full abstract on PubMed
Practical Takeaways
- •Delaying foal heat insemination until days 11-13 postpartum improves pregnancy rates in tropical grazing mares, contrary to earlier breeding attempts
- •Monitor follicle size and uterine edema as practical markers—larger follicles (>48 mm) with lower edema scores predict better conception outcomes
- •Under tropical rainforest permanent grazing conditions with uncomplicated foalings, expect approximately 7 in 10 mares to conceive at appropriately-timed foal heat insemination
Key Findings
- •71% pregnancy rate achieved when Colombian Paso Fino mares were inseminated at foal heat occurring between days 11-13 postpartum
- •Pregnant mares had significantly larger pre-ovulatory follicles (48.57 ± 0.8 mm) compared to non-pregnant mares (42.99 ± 1.0 mm)
- •Non-pregnant mares ovulated earlier (days 7-9 postpartum) with faster follicle growth rates than pregnant mares (days 11-13 postpartum)
- •Lower uterine edema scores on ovulation day in pregnant mares (2.93 ± 0.32 mm) versus non-pregnant mares (4.47 ± 0.05 mm) correlated with pregnancy success