Patterns of conceptus development and of progesterone concentrations in maternal blood preceding spontaneous early pregnancy failure in mares.

The research study explored patterns of early pregnancy loss in horses, with a focus on the role of progesterone levels and physical development stages of the conceptus. The researchers suggest that while various factors contribute to early pregnancy loss, luteolysis (degeneration of the corpus luteum, producing progesterone) could play a key part more often than previously thought.

Study Methodology and Findings

• The study involved 16 cases of spontaneous pregnancy loss in mares, 11 of which involved singletons (single foetuses) and five involved twins.
• These losses occurred between gestation Days 13 and 25.
• To monitor and record data, the researchers used transrectal ultrasonography to measure the growth of the conceptus (embryo and its associated structures), and determined maternal plasma progesterone concentrations through blood sampling.
• Out of the total cases, ten mares had their uteruses flushed, and eight conceptuses were recovered for morphological assessment.
• They observed that five out of the 11 singletons’ loss occurred before Day 16, accompanied or preceded by luteolysis in all but one case.
• Six singleton pregnancies failed after Day 16, two of which exhibited evidence of luteolysis.
• Hence, more than half of the singleton losses were associated with luteolysis, while the rest were not.

A Unique Case of Twins

• The study also presented a unique circumstance where twin conceptuses were involved.
• All five cases of twin losses happened on Day 19 or 20, with only one case showing signs of luteolysis beforehand.

Overall Conclusion

• The findings of the study indicate that the causes of spontaneous early pregnancy failure in mares are multifactorial.
• However, the research indicates that luteolysis could contribute to these issues more frequently than earlier studies suggested.
• The patterns of conceptus development and progesterone concentrations in maternal blood preceding early pregnancy failure warrant further research to confirm these observations and understand their implications better.