Physiological responses in nonheat acclimated horses performing treadmill exercise in cool (20°C/40%RH), hot dry (30°C/40%RH) and hot humid (30°C/80%RH) conditions

Abstract

Summary The aim of the present study was to determine the effect of different environmental conditions on physiological response to exercise. Four winter acclimatised, nonheat acclimated horses of different breeds were exercised at 20°C/40%RH (CD), 30°C/40%RH (HD) and 30°C/80%RH (HH). The exercise test was designed to represent the structure and intensity of a One star Speed and Endurance test (competition exercise test [CET]). All 4 horses were able to complete the full CET (60 min + 30 min active recovery) in CD and HD, but only one horse completed the CET in HH. Two horses were stopped because of pronounced general fatigue and one because of a right atrial temperature (TRA) of 43°C. Oxygen uptake on each phase was not different between CD and HD, but was higher during Phases B, C and D in HH. Mean peak TRA at the end of Phase D was 40.3 ± 0.2, 41.6 ± 0.4 and 42 ± 0.3°C for CD, HD and HH, respectively. Corresponding, mean peak rectal temperatures (TREC) following Phase D were 39.5 ± 0.1, 40.6 ± 0.1 and 41.5 ± 0.1°C for CD, HD and HH, respectively. Mean time to peak TREC was 9.3 ± 1.1 (CD), 7.3 ± 1.8 (HD) and 10.8 ± 2.3 (HH) min and was not significantly different between conditions (P>0.05). Heat dissipation amounted to 83 ± 1, 73 ± 2 and 70 ± 1% of heat production in CD, HD and HH, respectively. Weight loss was significantly correlated with both body surface area (CD r = 0.85; HD r = 0.87; HH r = 0.81) and bodyweight (CD r = 0.97; HD r = 0.93; HH r = 0.94). The greatest weight loss recorded was 4.6% bodyweight in one horse in HD. The mean increase in exercise intensity over the whole CET (in terms of V̇O2) of HD and HH compared with CD was 5 ± 3 and 14 ± 3% higher, respectively. The exercise induced hyperthermia and the reduced capacity for heat dissipation produced partial compensatory responses in minute ventilation (V̇E), particularly during Phase C, when the horses were trotting. In HD, the increase in V̇E was achieved mainly through an increase in frequency, whilst in HH it was achieved through an increase in tidal volume (VT). The horses demonstrated a high degree of tolerance to environmental heat load, suggesting a high thermoregulatory capacity. However, for unacclimatised animals exercising in severely hot and humid conditions, performance may be limited.

Effect of repeated exercise and recovery on heart rate variability in elite trotting horses during high intensity interval training

“…In this case, breathing frequency was not combined with stride frequency (Art et al 1990). The increase in breathing frequency could be a consequence of the increase in blood lactate concentration (Erickson et al 1991;McDonough et al 2002) and/or hyperthermia (Marlin et al 1996) during high speed repetitions. This is consistent with the increase in HR and decrease in RMSSD observed during exercise bouts.…”

Practical assessment of heart rate response to exercise under field conditions

“…In addition the results, as well as being influenced by the rider, can be influenced by the terrain 5 and other environmental factors 6 , particularly if the test used is not of short duration. A number of field-based tests have been described, but they often rely on the availability of measured tracks and large, open spaces.…”

Effects of a pre‐moistened multilayered breathable fabric in promoting heat loss during recovery after exercise under hot conditions

“…Horses generate considerable internal heat burdens when exercising over long periods of time, particularly under hot and/or humid conditions (Foreman et al 1995;Geor et al 1995Geor et al , 2000Marlin et al 1996;Kohn et al 1999a). Data generated before the 1996 Atlanta Olympic Summer Games showed that multiple applications of nearly-ice-cold water to the horse's dorsum was a superior method of cooling post exercise compared to the conventional use of water baths of ambient temperature (Williamson et al 1995;Foreman et al 1996b;Kohn et al 1999b).…”