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Asynchronous ovulation in mares: seasonal variations in frequency.

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Asynchronous double ovulation in mares is common, occurring more frequently during seasonal transitions. Close monitoring for double ovulation up to 96 hours post-ovulation is crucial for early detection of multiple pregnancies.

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Area of Science:

  • Equine reproduction
  • Veterinary science
  • Reproductive endocrinology

Background:

  • Mare reproductive cycles can result in multiple ovulations, primarily double ovulations.
  • Double ovulations can be synchronous or asynchronous, with asynchrony posing challenges for early pregnancy detection due to varying embryonic vesicle sizes.
  • Understanding the incidence and timing of double ovulation is critical for equine breeders and veterinarians.

Purpose of the Study:

  • To document the incidence of synchronous and asynchronous double ovulations in mares.
  • To determine if the occurrence of asynchronous double ovulation varies by month or season.

Main Methods:

  • Monitoring 506 estrous cycles from double-ovulating mares at 8±1 hour intervals.
  • Tracking ovulation timing from before expected ovulation up to 96 hours post-initial ovulation.
  • Grouping mares by ovulation intervals and month/season to analyze asynchrony patterns.

Main Results:

  • A significant difference was found between synchronous and asynchronous double ovulations, with asynchronous ovulations being more prevalent (65.8% vs. 34.2% for ≥8 hours asynchrony; 28.5% vs. 71.5% for ≥24 hours asynchrony).
  • Asynchronous ovulations occurred significantly more often during seasonal transition periods.
  • Asynchrony of up to 96 hours was observed, leading to significant differences in embryonic vesicle size.

Conclusions:

  • Asynchronous double ovulation is a common occurrence in mares.
  • The incidence of asynchronous double ovulation is higher during seasonal transition periods.
  • Close monitoring of mares for double ovulation up to 96 hours post-initial ovulation is essential, especially at the breeding season's extremes, to improve early detection of multiple pregnancies.