The nature of embryo reduction in mares with twin conceptuses: deprivation hypothesis.

This research explores whether embryo reduction occurs in mares with twin conceptuses, particularly when one embryonic vesicle’s wall is against the other’s instead of the endometrium, applying the “deprivation hypothesis”. In addition, it examines how ovulatory patterns – synchronous and asynchronous – influence the incidence of embryo reduction.

Research Methodology

• The researchers utilized ultrasonography as the primary method of observation and data gathering. This technology allowed them to visualize and track the development and state of the twin embryonic vesicles.
• Twin vesicles were detected using ultrasonography from days 11 to 15 (with ovulation considered as day 0). This was done daily up until the embryo reduction was observed or until day 40, whichever came first.

Findings

• 31 mares with twin embryonic vesicles were studied. Unilateral fixation was observed more frequently (71%) in comparison to bilateral fixation (29%). This indicates that in most cases, one embryonic vesicle’s wall was adjacent to the other’s, rather than the endometrium, supporting the deprivation hypothesis.
• The research also focused on mares with known ovulatory patterns. They found that in cases of synchronous ovulations, the type of fixation (either unilateral or bilateral) was not affected. However, for mares with asynchronous ovulation, unilateral fixation was more frequent, suggesting a link between ovulatory patterns and fixation type.
• The incidence of embryo reduction was observed to be greater in cases of unilateral fixation and asynchronous ovulation. This upholds the deprivation theory, suggesting that one twin can essentially deprive the other of necessary contact with the endometrium, potentially causing the other embryo to be reduced.
• The research found that in the cases where there were embryo reductions, the reduction often occurred before the detection of both embryo propers.