Middle Gluteal and Pectoral Muscle Cooling Rates in Thoroughbred Racehorses Undergoing Exercise on a Racetrack and High-Speed Treadmill

Advances in microchip technology have allowed for monitoring of body temperature in horses using percutaneous thermal-sensing microchips (PTSM). Using PTSM in exercising horses offers a more practical means of collecting temperature from the middle gluteal (GLUT) and pectoral (PECT) muscles. Previous work has shown that the PECT is a better proxy for core body temperature, but the GLUT is used during exercise by the horse for locomotion and likely cools differently than the PECT. However, research comparing the cooling rates between the GLUT and PECT when horses engage in different modes of exercise is scarce. Thus, the study objective was to compare cooling rates of GLUT and PECT after exercise in horses undergoing a standardized exercise test (SET) both under saddle on a racetrack and on a high-speed treadmill. Eight mature Thoroughbred racehorses with PTSM in the GLUT and PECT underwent SETs on a 1,200-m dirt-sand racetrack under saddle. Horses wore on-board heart rate monitors with GPS to track distance, speed, and duration of exercise. The racetrack SET was then replicated on a high-speed treadmill at 3° incline. After each SET, horses underwent a 10-min walk and 5-min hose, and then were placed in individual box stalls with a high-speed fan for 45 min. Temperatures were collected every 5 min until 60 min post-exercise. Changes in GLUT and PECT temperature from pre-exercise were fitted to an exponential one-phase decay model within GraphPad Prism (v10.4.1) to determine logarithmic rates of heat dissipation, expressed as cooling half-life (t_1/2). Individual t_1/2 data were analyzed within R Statistical Program (v4.4.0) using an ANOVA with results (mean ± SEM) separated using a Fisher’s LSD. GLUT temperatures immediately post-SET were 40.5 ± 0.2°C and 40.4 ± 0.2°C, and PECT temperatures were 40.7 ± 0.2°C and 40.4 ± 0.2°C for the racetrack and treadmill, respectively. The PECT cooled faster after racetrack exercise (t_1/2 = 12.8 ± 2.0 min) compared with treadmill (t_1/2 = 17.3 ± 2.0 min; P < 0.05), but the GLUT t_1/2 did not differ between the racetrack (t_1/2 = 18.2 ± 2.0 min) and treadmill (t_1/2 = 19.9 ± 2.0 min; P > 0.10). After the treadmill, the t_1/2 for GLUT and PECT did not differ (P > 0.10), but PECT cooled faster than GLUT after the racetrack SET (P < 0.05). These results indicate differences in cooling rates between GLUT and PECT when undergoing exercise on either racetrack or treadmill. However, GLUT did not differ by exercise mode, potentially indicating greater repeatability of GLUT measurements across multiple performance methods compared with PECT.

Springer, R.W., S. Dezalak, V.L. Erwin, I.N. Grayston, and J.D. Pagan. 2025. Middle gluteal and pectoral muscle cooling rates in Thoroughbred racehorses undergoing exercise on a racetrack and high-speed treadmill. Journal of Equine Veterinary Science 148:105539.