Comparison of daily heart rate and heart rate variability in trained and sedentary aged horses.

The research investigates the difference in heart rate and heart rate variability between trained and sedentary aged horses. Comparisons were made over the span of 22 hours and during the day and night, revealing that trained horses demonstrated a higher heart rate variability and a lower heart rate, potentially due to a reduced involvement of the sympathetic nervous system and increased parasympathetic activity during the day.

Objective of the Study

• The research aimed to compare the autonomic (self-regulatory) responses of trained and untrained aged horses by examining their daily heart rates and heart rate variability. This was done to better understand the impact of their physical activities on their heart function.

Methodology

• The study involved 22 horses; 11 aged horses that had undergone continuous training (TAH) and 11 sedentary aged horses (SAH).
• Heart rates (HR) and intervals between heartbeats (RR intervals) were observed over a 22-hour period, from 07.00h to 05.00h the following day, on an alternate day basis. In addition, these aspects were also monitored during daytime and nighttime.

Results

• The overall findings revealed that at night, there was an increase in RR intervals and parasympathetic nervous system (PNS) activity. These phenomena corresponded to a decrease in heart rate and sympathetic nervous system (SNS) activity.
• During the day, TAH showed lower mean HR and SNS index, but higher RR intervals and very-low-frequency bands, as compared to SAH. These findings suggest that TAH horses were more relaxed and demonstrated a higher level of parasympathetic activity (indicating a state of rest and digest) as opposed to the heightened sympathetic activity (indicating a fight or flight response) seen in SAH.
• The standard deviation of the RR intervals, which represents the variability in the heart rate, was found to be higher in TAH horses compared to the SAH group, both during the day and at night. This could suggest a better adaptation to environmental or physiological stressors by the TAH.

Implications

• The study inferred that aged horses with different physical activities have different autonomic responses, with TAH demonstrating higher heart rate variability than SAH during the day.
• It was postulated that this could be a result of reduced SNS activity, indicating a shift toward more parasympathetic (rest-and-digest) activity in TAH during the day.
• The findings prompt further research to understand the degree to which autonomic regulation is influenced by the level and regimen of exercise in aged horses.