24-hour secretion patterns of plasma oestradiol 17beta in pony mares in late gestation.

The research study aimed to investigate the relationship between the hormone oestradiol 17beta and the increased frequency of uterine contractions in pony mares at night during the final six days of gestation.

Objective and Hypothesis

• The objective of the research was to examine the 24-hour secretion pattern of a hormone called oestradiol 17beta (O17beta) in pregnant pony mares approaching parturition (also known as childbirth or delivery).
• The researchers hypothesized that O17beta might be connected with the increased occurrence of uterine contractions in mares during the night in the late stage of their pregnancy.

Methods

• The researchers studied 3 pony mares that were in the late stages of their gestation periods.
• Blood samples were collected in two stages. The initial samples were taken weekly at 8:00 AM starting from the 240th day of gestation, and then every third day from the 330th day of gestation until delivery. The second set of samples was collected beginning from the 310th day of gestation, with samples taken every 30 minutes for a 24-hour period, and then every sixth day until parturition.

Findings

• The researchers found that the levels of O17beta were significantly higher during the night, with the lowest concentrations being found just before sunset.
• The natural logarithm (or ln) of the variance, a measure of spread or dispersion in the data, increased significantly at sunset and decreased during the six-hour period immediately after sunrise. This increase at sunset is a key finding as it coincides with the period when mares typically have increased uterine contractions.
• This pattern was particularly noticeable in the final six days before parturition, suggesting that changing levels of O17beta could be contributing to nocturnal delivery in mares.

Conclusion

• The contrast between nocturnal and daytime concentrations of O17beta, the researchers believe, may play a role in the night-time delivery commonly witnessed in mares.
• The findings, however, represent a correlation and not causation, so further research would be required to definitively establish O17beta as a driver for increased uterine contractions and night-time delivery in mares.