[Double ovulation in mares. Clinical, hormone analytical and sonographic studies].

This research on 108 mares investigates the occurrence of double ovulation during 135 oestrous cycles. It compares synchronous and asynchronous double ovulation, examines the developmental changes and hormone levels in both instances, and discusses the potential connection to twin pregnancies in mares.

Methodology and Findings

• The study examines 108 mares across 135 oestrous cycles. Notably, about 30% of these mares develop double follicles, as identified through palpation and ultrasonography.
• The researchers closely studied eight instances of double ovulation. Four of these were synchronous, meaning both eggs released simultaneously, and four were asynchronous, where the time of release differed.
• In synchronous double ovulation, both follicles matured at the same pace and showed similar development. In contrast, with asynchronous ovulation, the second follicle continued to grow even after the first had ovulated.

Hormonal Analysis

• Regardless of whether ovulation was synchronous or asynchronous, equal levels of progesterone were detected in the mares’ blood. The progesterone level was low on the day of ovulation and started to increase from the day after.
• According to the study, double follicles tend to mature slower than single follicles.

Behavioral Observations and Pregnancy

• Mares with synchronous double ovulation exhibited typical oestrous behavior. However, this behavior was less pronounced after the first ovulation in mares with asynchronous double ovulation.
• Overall, from the four mares with asynchronous double ovulation and the two mares with synchronous ovulation, all became pregnant. Despite the occurrence of double ovulation, no twin pregnancies were recorded.

Possible Implications

• The lack of twins despite instances of double ovulation led researchers to consider possible links between double ovulation and twin pregnancies. Though specific conclusions aren’t reached, it lays the groundwork for further research into this topic.