Changes in heart rate and heart rate variability in Thoroughbreds during prolonged road transportation.
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.


METHODS
Five 2-year-old Thoroughbreds.


METHODS
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 (R(2) = 0.40) and by HF power and LF-to-HF ratio during road transportation (R(2) = 0.86).


CONCLUSIONS
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.
Ohmura
Hajime
H
Equine Science Division, Hidaka Training and Research Center, Japan Racing Association, 535-13 Aza-Nishicha, Urakawagun, Hokkaido 057-0171, Japan.
Hiraga
Atsushi
A
Aida
Hiroko
H
Kuwahara
Masayoshi
M
Tsubone
Hirokazu
H
Jones
James H
JH
D000818:Animals; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006736:Horses / Q000145:classification / Q000502:physiology*; D008297:Male; D013312:Stress, Physiological; D013997:Time Factors; D014195:Travel