Ovarian and Uterine Dynamics During the Estrous Cycle in Criollo Breed Mares.
Authors: Duval Luzia H, Rechsteiner Sandra M Fiala, Gastal Gustavo D A, Gastal Melba O, Mattos Rodrigo C, Gastal Eduardo L
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Ovarian and Uterine Dynamics in Criollo Mares Centuries of free-ranging reproduction in South America have shaped the Criollo breed into a notably hardy and enduring animal, yet reproductive physiology specific to this breed remains poorly characterised. Duval and colleagues used transrectal ultrasonography to track follicular and luteal dynamics across 26 consecutive oestrous cycles in 13 mares, documenting changes in cervical tone, uterine tone and endometrial echotexture throughout two complete cycles. The Criollo demonstrated a 21-day interovulatory interval with follicular deviation occurring at 22 mm (dominant) and 21 mm (subordinate) diameter, culminating in a preovulatory follicle of approximately 43 mm; the corpus luteum peaked two days post-ovulation before gradual regression, whilst cervical and uterine tones remained elevated until days 12–14 (expected luteolysis), and endometrial echotexture peaked 3–5 days before the subsequent ovulation. Notably, strong repeatability within individual animals was observed across multiple reproductive parameters, including preovulatory follicle diameter, cervical and uterine tone, and corpus luteum dimensions. For practitioners managing Criollo mares under breeding programmes, these findings provide baseline reference values for detecting oestrous cycle abnormalities, optimising breeding timing and identifying reproductive pathology; the breed's consistent cycle characteristics and individual repeatability suggest potential predictability for oestrous synchronisation and artificial breeding protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Breeding managers working with Criollo mares can expect consistent 21-day cycles with follicular deviation occurring at follicles of 21-22 mm diameter, allowing predictable breeding timing
- •Ultrasound monitoring shows clear uterine and cervical tone changes that correlate with reproductive status, providing practical non-invasive markers for estrus detection in this breed
- •Strong individual repeatability in follicular and luteal characteristics suggests Criollo mares show consistent reproductive patterns that can be tracked and predicted for each animal over time
Key Findings
- •Criollo mares have 21-day interovulatory intervals with dominant and subordinate follicles emerging together at day 5 post-ovulation
- •Deviation between dominant and subordinate follicles occurs at 22 mm and 21 mm diameter respectively, with preovulatory follicles reaching mean diameter of 43 mm
- •Corpus luteum reaches maximum diameter 2 days post-ovulation and decreases gradually; luteolysis occurs at days 12-14
- •Cervical and uterine tones remain elevated until expected luteolysis; endometrial echotexture peaks 5-3 days before ovulation with strong within-animal repeatability