Effects of pre-cooling on thermophysiological responses in elite eventing horses

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.