Asynchronous ovulation in mares: seasonal variations in frequency.
Authors: Morel M C G Davies, Newcombe J R, Reynolds N
Journal: The Veterinary record
Summary
# Editorial Summary Double ovulations in mares present a significant breeding challenge, yet the timing relationship between these ovulations—particularly asynchronous patterns where ovulations occur more than eight hours apart—remains poorly characterised in clinical practice. Researchers at the Royal Veterinary College monitored 506 reproductive cycles in double-ovulating mares using ultrasound scanning at eight-hour intervals across a 96-hour window post-initial ovulation, stratifying data by calendar month to identify seasonal patterns. Asynchronous double ovulations proved remarkably common, occurring in 65.8% of cycles when defined as ≥8 hours apart and 28.5% when using a ≥24-hour threshold; critically, asynchrony was significantly more frequent during spring and autumn transition periods (P<0.05). These findings have direct implications for veterinary practitioners and breeders: the substantial prevalence of asynchronous ovulations means that embryonic vesicles of markedly different developmental stages may be present during early pregnancy diagnosis, substantially increasing the risk of missing multiple gestations if scanning protocols fail to extend surveillance to the full 96-hour window, particularly during seasonal transitions when asynchrony is most pronounced.
Read the full abstract on PubMed
Practical Takeaways
- •Monitor double-ovulating mares closely for up to 96 hours after the first ovulation, particularly during spring and autumn transitions, to reliably detect asynchronous ovulations
- •Use 8±1 hour monitoring intervals during the ovulation window to accurately detect the timing of both ovulations and reduce the risk of missing pregnancies
- •Be aware that asynchronous embryonic development can make early pregnancy detection challenging; rescanning mares with suspected multiple ovulations may be warranted if initial ultrasound is equivocal
Key Findings
- •65.8% of double ovulations were asynchronous (≥8 hours apart) and 28.5% were asynchronous (≥24 hours apart), compared to 34.2% and 71.5% synchronous respectively
- •Asynchronous double ovulations occurred significantly more frequently during seasonal transition periods (P<0.05)
- •Asynchrony of up to 96 hours can result in embryonic vesicles of markedly different sizes that are challenging to detect on early ultrasound
- •Monitoring mares up to 96 hours post-initial ovulation is necessary to detect multiple pregnancies and minimize missed diagnoses