Seasonal absence of supplementary corpora lutea in pregnant mares and the relationship with pregnancy loss.
Authors: Newcombe John R, Wilsher Sandra, Silva Elisa S M, Sala-Ayala Laura, Cuervo-Arango Juan
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Researchers in the UK and Brazil investigated whether the season of conception affects the development of supplementary corpora lutea (SCL)—additional progesterone-producing structures beyond the primary CL—and whether their absence increases pregnancy loss risk. Following 199 pregnancies from conception through to day 120, they found that 75.8% of mares conceiving during the breeding season (March–September) developed at least one SCL, compared with only 33% of those conceiving during the non-breeding season (October–February), suggesting photoperiod and seasonal gonadotropin patterns regulate SCL formation. Contrary to expectations, pregnancy loss rates between days 35 and 120 were similar in mares with no SCL (3.5%) and those with SCL (1.4%), indicating that SCL absence does not predispose to early pregnancy loss. These findings challenge the assumption that supplementary corpora lutea are necessary for pregnancy maintenance in mares and suggest that whilst season profoundly influences their development, their presence or absence has minimal clinical significance for pregnancy viability—an important consideration when counselling clients about conception timing and managing mares conceiving outside the traditional breeding window.
Read the full abstract on PubMed
Practical Takeaways
- •The presence or absence of supplementary corpora lutea should not be used as a predictor of pregnancy viability or loss in mares during routine ultrasound examinations
- •Seasonal variation in supplementary corpora lutea development is normal and photoperiod-dependent; absence during non-breeding season conceptions requires no clinical intervention
- •Embryo transfer timing and recipient mare selection based on ovarian cyclicity status may influence supplementary corpora lutea development, but this does not affect pregnancy outcome
Key Findings
- •Pregnancies conceived during breeding season (March-September) were significantly more likely to develop supplementary corpora lutea (75.8%) compared to non-breeding season conceptions (33%)
- •Pregnancy loss between Days 35-120 was similar regardless of supplementary corpora lutea presence (3.5% without vs 1.4% with SCL, P>0.1)
- •Supplementary corpora lutea development is regulated by photoperiod and seasonal variation in gonadotropin concentrations, evidenced by higher development in cyclic and transitional mares (100% and 86%) versus anestrous mares (50%)
- •Absence of supplementary corpora lutea does not increase pregnancy loss risk in mares