Relationship between early pregnancy site in consecutive gestations in mares

Area of Science:

• Reproductive biology
• Veterinary medicine
• Equine science

Background:

• Understanding uterine horn dynamics is crucial for equine reproductive success.
• Consecutive pregnancies in mares present unique physiological challenges.
• Previous research has not fully elucidated the contralateral uterine horn preference in sequential equine pregnancies.

Purpose of the Study:

• To investigate the uterine horn preference for initial pregnancy establishment in consecutive pregnancies in mares.
• To determine if the interval between parturition and conception influences uterine horn selection.
• To assess the impact of early versus late-term abortion on subsequent pregnancy horn localization.

Main Methods:

• Retrospective analysis of 200 pairs of consecutive pregnancies in mares.
• Recording the uterine horn of initial pregnancy establishment for both consecutive pregnancies.
• Categorizing pregnancy outcomes, including live births and abortions (early <140 days, late >140 days).

Main Results:

• 82% of mares established their second pregnancy in the contralateral uterine horn compared to the first.
• This contralateral preference was observed irrespective of the time interval between parturition and conception.
• The contralateral horn preference persisted when the first pregnancy was aborted after 140 days, but not before.

Conclusions:

• Mares exhibit a strong contralateral uterine horn preference for sequential pregnancies.
• This phenomenon is independent of the inter-pregnancy interval.
• Late-term abortion does not disrupt the contralateral horn preference, suggesting a robust physiological mechanism.