Heart rate and heart rate variability in the pregnant mare and its foetus.

This research investigates the changes in heart rate and heart rate variability in pregnant mares and their foetuses. The goal was to establish normal values and track changes during pregnancy to enhance the monitoring of risk pregnancies among horses and initiate timely treatment interventions.

Objective and Methodology of the Study

• The study aimed to identify the normal values of heart rate, represented as HR, and heart rate variability, presented as HRV, in pregnant mares and compare these with the foetus’ heart rates. Additionally, it intended to monitor physiological changes during the course of pregnancy.
• The mares’ RR interval (the time between consecutive R-waves of the QRS signal on the electrocardiogram) was measured, and any changes in the RR interval and HRVs during the progression of gestation were noted.

Findings of the Study

• In mares, the RR interval was found to decrease from the 270th to the 330th day of pregnancy. At the same time, the foetal RR interval increased.
• This inversely proportional change was mirrored in the mares’ and the foetus’ heart rates, whereby the mare’s heart rate increased while the foetus’ heart rate decreased.
• The last 10 days before foaling witnessed no further changes in either the mare’s or foetus’ RR intervals. Similarly, Mother’s HRV did not change during pregnancy.
• In the hours leading up to parturition, the mother’s RR interval was lower than at any other point during pregnancy. However, this value remained constant during these final hours.
• Significant changes in HRV, marked by a sharp increase, were only noted during the last minutes before foaling.

Conclusions of the Study

• The cardiovascular system of pregnant mares adapted to the physiological demands of ongoing pregnancy by increasing heart rate. This adaptation indicates a healthy response to pregnancy.
• The study found no evidence that healthy mares find pregnancy a major stressor, based on their heart rate and heart rate variability readings.
• Such detailed insights into the cardiovascular response of pregnant mares can assist veterinary practitioners in closely monitoring risk pregnancies and allowing timely intervention.