Diestrous Ovulations in Pregnant Mares as a Response to Low Early Postovulatory Progestogen Concentration.
Authors: Okada Carolina T C, Kaps Martim, Perez Quesada Javier, Gautier Camille, Aurich Jörg, Aurich Christine
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Spontaneous formation of secondary corpora lutea (CLs) during early equine pregnancy remains poorly understood, though it may compromise reproductive outcomes if not managed appropriately. Researchers investigated whether inadequate early progesterone secretion following ovulation could trigger compensatory luteal development in pregnant mares (n=11) by deliberately suppressing postovulatory progestogen with the PGF2α analogue cloprostenol during days 0–3 post-ovulation, then reversing treatments in a second pregnancy cycle. Mares receiving early PGF2α treatment exhibited significantly elevated LH concentrations during subsequent pregnancy (p<0.05), greater total luteal tissue area when secondary CLs were present, and substantially lower early postovulatory progestogen levels compared to untreated controls (p<0.01). The findings suggest that suboptimal progesterone in the immediate postovulatory period reduces inhibitory feedback on the hypothalamic-pituitary axis during early pregnancy, allowing continued gonadotrophin stimulation and secondary CL formation—a mechanism that may explain why some pregnant mares develop diestrous ovulations. Practitioners should recognise that detection of secondary CLs at routine pregnancy examination may indicate compromised early luteal function rather than a pathological response, potentially warranting targeted progesterone support during the critical postovulatory window in mares with a history of suboptimal luteal development.
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Practical Takeaways
- •Detection of secondary corpus luteum on ultrasound during early pregnancy examination in mares may indicate that early postovulatory progesterone levels were suboptimal, potentially warranting progestin supplementation in future cycles
- •Early luteal phase support (days 0-3 post-ovulation) may be important for preventing diestrous ovulations in pregnant mares, particularly in mares with history of secondary corpus luteum formation
- •Clinicians should monitor gonadotrophin patterns and luteal function in early pregnancy, as aberrant LH secretion due to low progesterone may predispose to unwanted secondary ovulations
Key Findings
- •PGF2α treatment in early postovulation (days 0-3) reduced progestogen concentration and stimulated secondary corpus luteum formation during pregnancy (p < 0.01)
- •Mares with diestrous corpus luteum during PGF treatment pregnancy showed greater total luteal tissue area compared to primary corpus luteum group
- •LH concentration was significantly higher in PGF2α-treated pregnancies than untreated pregnancies (p < 0.05), but FSH did not differ between groups or treatments
- •Low early postovulatory progestogen reduces negative feedback on the hypothalamic-pituitary axis, triggering luteal tissue response and secondary ovulation during pregnancy