Progesterone concentrations in the peripheral plasma of the mare during pregnancy.

This research investigates how the concentration of progesterone, a hormone vital in pregnancy, changes in mares throughout gestation and immediately after giving birth. Using plasma samples, the study found variations in progesterone levels across different stages of pregnancy and among individual mares.

Study Methodology

• Progesterone concentration was measured using a protein-binding assay, a biochemical procedure used for determining the concentration of a specific protein in a solution.
• Samples of peripheral plasma were taken from eight thoroughbred mares at different stages of their pregnancy and for two days following parturition, or childbirth.
• The choice of thoroughbred mares was to ensure a high-purity sample and consistent results.

Findings

• Individual variability was observed: the same stage of pregnancy showed notably different progesterone levels among different mares.
• On average, progesterone levels raised during the initial 60 days of gestation.
• There was a fall in progesterone levels around the 180-day mark, which is when the accessory corpora lutea—a temporary endocrine structure involved in pregnancy—regresses.
• The concentration peaked within the period starting from the 270th day to term (end of pregnancy) with an average of 11.5 ng/ml. This result was significantly higher than 7.6 ng/ml, the mean level for the entirety of the gestation period.

Post-Partum Observations

• During the two days post-partum (after childbirth), a considerable drop in progesterone concentration was recorded, with an average of 0.5 ng/ml. Such a sharp decrease highlights the hormone’s primary role in maintaining pregnancy.

Implications and Conclusion

• The study offers valuable insights into the process of pregnancy and childbirth in mares, emphasizing the critical role of progesterone. Mapping progesterone levels throughout gestation could be helpful in monitoring the health and progress of equine pregnancy.
• The notable difference in hormone levels among individual horses at the same gestation stage suggests that more personalized, case-specific approaches might be needed in equine pregnancy management and care.
• Further research could focus on why these individual differences occur, and how they might influence the pregnancy’s outcome.