Using Percutaneous Thermal-Sensing Microchips to Assess the Efficacy of Active Versus Passive Cooling in Exercising Thoroughbred Horses: An Integrative Data Analysis

Percutaneous thermal sensing microchips (PTSM) have been introduced as more practical alternatives for muscle temperature monitoring during and after exercise in horses (Kang et al., 2020). Our objective was to determine the efficacy of different cooling methods using PTSM employing an integrative data analysis. We implanted PTSM in the gluteal muscle (GLUT; total depth: 2.27 ± 0.45 cm; muscle depth: 1.81 ± 0.56 cm) of eight 2-year-old and 20 mature Thoroughbreds. Twelve of the mature horses also had pectoral (PECT) PTSM implanted (total depth: 1.61 ± 0.31 cm; muscle depth: 1.42 ± 0.31 cm). All horses were in active training, considered fit, and underwent standardized exercise tests (SETs; n = 248) on a racetrack (n = 80) or high-speed treadmill (n = 168) over 13 separate studies from August 2023 to November 2024. Studies were completed during hot (>30°C; n = 5), moderate (20–30°C; n = 3), and cool conditions (<20°C; n = 5). Racetrack SETs consisted of up to a 1,200-m gallop (8–10 m/s) and a 600-m breeze (12.5–14.5 m/s). Treadmill SETs were incremental step tests up to 10 m/s with a 3° incline. Following exercise, horses underwent either active (hosing, misting; n = 183) or passive cooling (walking, standing in a stall; n = 65) using the PTSM to measure efficacy. Muscle temperatures, ambient temperature, and relative humidity were collected before, immediately after, and every 5 min until 60 min post-exercise. Changes in GLUT and PECT temperature from pre-exercise were fitted to an exponential 1-phase decay model to determine logarithmic rate of heat dissipation and expressed as cooling half-life (t_1/2). Muscle temperature data were analyzed using an ANCOVA. Active cooling enhanced t_1/2 of the GLUT and PECT compared with passive (P < 0.05; P < 0.05; Table 1). Ambient temperature and relative humidity were significant covariates (P < 0.001; P < 0.001). Overall, PTSM implanted in the GLUT and PECT of Thoroughbred horses produced no adverse reactions and were easy to use. Furthermore, PTSM are useful to monitor muscle temperature during and after exercise, and to determine efficacy of different cooling modalities under various exercises.

Pagan, J.D., and R.W. Springer. 2025. Using percutaneous thermal-sensing microchips to assess the efficacy of active versus passive cooling in exercising Thoroughbred horses: An integrative data analysis. Journal of Equine Veterinary Science 148:105538.