Effects of Pre-Cooling on Thermophysiological Responses in Elite Eventing Horses

Abstract

In this study, we examined the effects of pre-cooling on thermophysiological responses in horses exercising in moderate environmental conditions (average wet bulb globe temperature: 18.5 ± 3.8 °C). Ten international eventing horses performed moderate intensity canter training on two separate days, and were either pre-cooled with cold-water rinsing (5-9 °C for 8 ± 3 min; cooling) or were not pre-cooled (control). We determined velocity (V), heart rate (HR), rectal temperature (T_re,), shoulder and rump skin temperature (T_shoulder and T_rump), plasma lactate concentration (LA), gross sweat loss (GSL), and local sweat rate (LSR), as well as sweat sodium, chloride and potassium concentrations. The effect of pre-cooling on T_re was dependent on time; after 20 min of exercise the effect was the largest (estimate: 0.990, 95% likelihood confidence intervals (95% CI): 0.987, 0.993) compared to the control condition, resulting in a lower median T_re of 0.3 °C. Skin temperature was also affected by pre-cooling compared to the control condition (T_shoulder: -3.30 °C, 95% CI: -3.739, -2.867; T_rump: -2.31 °C, 95% CI: -2.661, -1.967). V, HR, LA, GSL, LSR and sweat composition were not affected by pre-cooling. In conclusion, pre-cooling by cold-water rinsing could increase the margin for heat storage, allowing a longer exercise time before a critical T_re is reached and, therefore, could potentially improve equine welfare during competition.

Keywords: horses; pre-cooling; rectal temperature; sweat composition; sweat rate.

Figure 1

Measurement locations of the skin temperature sensors, represented by the grey cycles (a = shoulder; and b = rump), and absorbent sweat patches, represented by the black rectangles (1 = neck; 2 = barrel; and 3 = rump).

Figure 2

Mean and standard deviation of the physiological responses of ten international eventing horses in the Netherlands (average wet bulb globe temperature: 18.5 ± 3.8 °C). The data are shown for the warm-up and canter training with either pre-cooling (cooling) or not (control) in between. (a) Heart rate (HR); (b) rectal temperature (T_re); (c) shoulder skin temperature (T_shoulder); and (d) rump skin temperature (T_rump). * Denotes an effect of cooling. ^φ Denotes an interaction effect of time x cooling.