AUTHOR=Verdegaal Elisabeth-Lidwien J. M. M. , Howarth Gordon S. , McWhorter Todd J. , Boshuizen Berit , Franklin Samantha H. , Vidal Moreno de Vega Carmen , Jonas Stacey E. , Folwell Louise E. , Delesalle Catherine J. G. 

TITLE=Continuous Monitoring of the Thermoregulatory Response in Endurance Horses and Trotter Horses During Field Exercise: Baselining for Future Hot Weather Studies

JOURNAL=Frontiers in Physiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.708737

DOI=10.3389/fphys.2021.708737

ISSN=1664-042X

ABSTRACT=<p>Establishing proper policies regarding the recognition and prevention of equine heat stress becomes increasingly important, especially in the face of global warming. To assist this, a detailed view of the variability of equine thermoregulation during field exercise and recovery is essential. 13 endurance horses and 12 trotter horses were equipped with continuous monitoring devices [gastrointestinal (GI) pill, heartrate (HR) monitor, and global positioning system] and monitored under cool weather conditions during four endurance rides over a total of 80 km (40 km loops) and intense trotter track-based exercise over 1,540 m. Recordings included GI temperature (T<sub><italic>c</italic></sub>), speed, HR and pre- and post-exercise blood values. A temperature time profile curve of T<sub><italic>c</italic></sub> was constructed, and a net area under the curve was calculated using the trapezoidal method. Metabolic heat production and oxygen cost of transport were also calculated in endurance horses. Maximum T<sub><italic>c</italic></sub> was compared using an independent samples <italic>t</italic>-test. Endurance horses (mean speed 14.1 ± 1.7 km h<sup>–1</sup>) reached mean maximum T<sub><italic>c</italic></sub> (39.0 ± 0.4°C; 2 × 40 km in 8 horses) during exercise at 75% of completion of T<sub><italic>c</italic></sub> exercise and T<sub><italic>c</italic></sub> returned to baseline within 60 min into recovery. However, the mean T<sub><italic>c</italic></sub> was still 38.8 ± 0.4°C at a HR of 60 bpm which currently governs “fit to continue” competition decisions. Trotters (40.0 ± 2.9 km h<sup>–1</sup>) reached a comparable mean max T<sub><italic>c</italic></sub> (38.8 ± 0.5°C; 12 horses) always during recovery. In 30% of trotters, T<sub><italic>c</italic></sub> was still &gt;39°C at the end of recovery (40 ± 32 min). The study shows that horses are individuals and thermoregulation monitoring should reflect this, no matter what type of exercise is performed. Caution is advised when using HR cut-off values to monitor thermal welfare in horses since we have demonstrated how T<sub><italic>c</italic></sub> can peak quite some time after finishing exercise. These findings have implications for training and management of performance horses to safeguard equine welfare and to maximize performance.</p>