Objective—To determine the effects of immersion in
warm springwater (38° to 40°C) on autonomic nervous
activity in horses.
Animals—10 male Thoroughbreds.
Procedure—Electrocardiograms were recorded from
horses for 15 minutes during a warm springwater bath
after being recorded for 15 minutes during stall rest.
Variations in heart rate (HR) were evaluated from the
power spectrum in terms of low frequency (LF, 0.01 to
0.07 Hz) power and high frequency (HF, 0.07 to 0.6 Hz)
power as indices of autonomic nervous activity.
Results—Mean (±SE) HR during stall rest and immersion
in warm springwater was 31.1 ± 1.7 and 30.3 ±
1.0 beat/min, respectively. No significant difference
was found between the HR recorded during stall rest
and that recorded during immersion in warm springwater.
The HF power significantly increased from
1,361 ± 466 milliseconds2 during stall rest to 2,344 ±
720 milliseconds2 during immersion in warm springwater.
The LF power during stall rest and immersion
in warm springwater was 3,847 ± 663 and 5,120 ±
1,094 milliseconds2, respectively, and were not significantly
different from each other. Similarly, the LF:HF
ratio did not change during immersion in warm springwater.
The frequency of second-degree atrioventricular
block, which was observed in 2 horses, increased
during immersion in warm springwater, compared
with during stall rest.
Conclusions and Clinical Relevance—Increases in
HF power indicates that the parasympathetic nervous
activity in horses increases during immersion in warm
springwater. Thus, immersion in warm springwater
may provide a means of relaxation for horses. ( Am J
Vet Res 2003;64:1482–1485)