Objective—To determine the effects of initial handling
and training on autonomic nervous functions in
Animals—63 healthy Thoroughbreds.
Procedure—All horses were trained to be handled
and initially ridden in September of the yearling year
and then trained until the following April by conventional
training regimens. To obtain the heart rate (HR),
electrocardiograms were recorded in the stable
before initial handling and training and following 7
months of training; variations in HR were then evaluated
from the power spectrum in terms of the 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. To evaluate the fitness, the V200
(velocity at HR of 200 beat/min), which is reflective of
the aerobic capacity of the horse, was measured.
Results—Mean (± SE) resting HR decreased significantly
from 41.5 ± 0.8 to 38.7 ± 0.4 beat/min following
7 months of training. The LF power of horses
increased significantly from 1,037 ± 128 milliseconds2
in September of the yearling year to 2,944 ± 223 milliseconds2
in the following April. Similarly, the HF
power increased significantly from 326 ± 30 milliseconds2
to 576 ± 39 milliseconds2 at the corresponding
time points. The V200 increased significantly following
Conclusions and Clinical Relevance—Increases in
LF and HF powers indicate that parasympathetic nervous
activity increases in horses by 7 months of training.
The decrease in resting HR may be dependent on
the training-induced increase of parasympathetic nervous
activity in Thoroughbreds. (Am J Vet Res
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)
Objective—To determine whether evaluation of heart rate (HR) and HR variability (HRV) during prolonged road transportation in horses provides a sensitive index of autonomic stimulation.
Animals—Five 2-year-old Thoroughbreds.
Procedure—ECGs were recorded as horses were transported for 21 hours in a 9-horse van. Heart rate, high-frequency (HF) power, low-frequency (LF) power, and LF-to-HF ratio from Fourier spectral analyses of ECGs were calculated and compared with values recorded during a 24-hour period of stall rest preceding transportation.
Results—HR, HF power, and LF power had diurnal rhythms during stall rest but not during road transportation. Heart rate was higher and HF power and LF power lower during road transportation than stall rest, and HR, HF power, LF power, and LF-to-HF ratio all decreased with time during road transportation. Heart rate during stall rest was weakly and inversely associated with LF power, but during road transportation was strongly associated with LF power, HF power, and LF-to-HF ratio. Neither LF power nor HF power was correlated with LF-to-HF ratio during stall rest, but LF power was strongly and HF power weakly correlated with LF-to-HF ratio during road transportation. High-frequency power and LF power were significantly correlated with each other during stall rest and road transportation. Heart rate was significantly influenced by LF power and LF-to-HF ratio during stall rest (R2 = 0.40) and by HF power and LF-to-HF ratio during road transportation (R2 = 0.86).
Conclusions and Clinical Relevance—HR is influenced by different sympathovagal mechanisms during stall rest, compared with during road transportation; HRV may be a sensitive indicator of stress in transported horses.