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 (Tre,), shoulder and rump skin temperature (Tshoulder and Trump), 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 Tre 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 Tre of 0.3 °C. Skin temperature was also affected by pre-cooling compared to the control condition (Tshoulder: −3.30 °C, 95% CI: −3.739, −2.867; Trump: −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 Tre is reached and, therefore, could potentially improve equine welfare during competition.

Is Continuous Monitoring of Skin Surface Temperature a Reliable Proxy to Assess the Thermoregulatory Response in Endurance Horses During Field Exercise?

“…Up until now, a limited number of studies, almost all of which were treadmill based, monitored the T sk continuously in the horses during the exercise and compared the T sk to T c ( 38 – 40 , 42 , 52 ). Only one recent field study has been performed, monitoring T sk and T re ( 20 ). The treadmill studies confirmed the lack of correlation between T sk and T c .…”

“…Several field studies have investigated less-invasive continuously monitoring approaches, such as the intra-uterine temperature (two mares) or the GI temperature; both approaches (intra-uterine and GI) showed a good correlation with the T c ( 18 , 19 , 68 ). A recent study has continuously monitored surface T sk using i-Button® and simultaneous T re during two canter bouts of 4.5 min of field exercise at a speed ranging from 6.7 to 7.5 meters per second ( 20 ). The T sk was continuously monitored at the level of the rump and shoulder regions in 10 eventing horses using a cross-over study design.…”

“…All were conducted in laboratory conditions, for example, on a treadmill ( 37 – 42 ). Only one study has recorded T sk continuously during a short bout of field exercise of 4.5-min duration to investigate the effect of pre-exercise cooling in 10 horses ( 20 ). The study recorded surface T sk using a microchip (i-Button®) attached to the skin with removable glue and simultaneously monitored rectal temperature (T re ) using a rectal probe; both T sk and T re reduced over time (3°C and 0.3°C, respectively).…”

“…To identify a reliable proxy for thermoregulatory response in the field, a solid correlation must exist between that specific proxy and T c evolvement, despite the existence of a time lag ( 24 , 47 ). However, currently, very few equine studies have involved the simultaneous continuous monitoring of T c (either using carotid artery temperature, or a GI pill, or the T re ), together with an additional temperature monitoring device during field exercise ( 19 , 20 , 51 ). On the other hand, with the ongoing development of new wearables and sensors, there are an increasing number of exercise studies investigating continuous T sk , monitoring wearables ( 20 , 37 – 40 , 42 , 52 ) (Supplementary Table 1 in Supplementary Material ).…”

“…However, currently, very few equine studies have involved the simultaneous continuous monitoring of T c (either using carotid artery temperature, or a GI pill, or the T re ), together with an additional temperature monitoring device during field exercise ( 19 , 20 , 51 ). On the other hand, with the ongoing development of new wearables and sensors, there are an increasing number of exercise studies investigating continuous T sk , monitoring wearables ( 20 , 37 – 40 , 42 , 52 ) (Supplementary Table 1 in Supplementary Material ). These devices all provide data output, although the physiological meaning of these data is not always clear.…”