Effects of Two Cooling Modalities on Temperature Recovery of Rectal, Middle Gluteal Muscle, and Pectoral Muscle Temperatures

Rectal temperature is commonly used to estimate core body temperature in horses but is impractical and unsafe. Percutaneous thermal-sensing microchips (PTSM) inserted into the middle gluteal (GLUT) and pectoral (PECT) muscles may be more practical for collecting temperature. Little work has determined how rectal temperature compares to middle gluteal and pectoral muscle temperatures under different cooling modalities. The study objective was to determine the effects of hosing or walking post-exercise on recovery of rectal, middle gluteal muscle, and pectoral muscle temperatures. Eight mature Thoroughbred horses with PTSMs in the GLUT and PECT were used in a 2-week crossover design. Treatments were hosing immediately after exercise for 5 min then walking for 10 min (HOSE) or walking for 15 min after exercise (WALK) following a standardized exercise test (maximum speed: 10 m/s; peak heart rate >200 beats/min). Horses stood in stalls with fans from 15 to 60 min post-exercise. Rectal, GLUT, and PECT temperatures were collected immediately before and after exercise, and then at predetermined intervals until 60 min of recovery. Change from pre-exercise temperatures for GLUT and PECT were fitted to an exponential 1-phase decay model to determine recovery rate via half-life (t_1/2) in GraphPad Prism (v10.4.1). Data were further analyzed using a 3-way repeated measures ANOVA in R Statistical Program (v4.4.0). Results were considered significant at P ≤ 0.05. Ambient temperature and relative humidity (mean ± SD) were 34.1 ± 1.5°C and 53.8 ± 10.9%, pooled across both periods. Peak GLUT and PECT temperatures (mean ± SEM) were 40.8 ± 0.3°C and 41.0 ± 0.3°C, respectively. HOSE decreased GLUT and PECT temperatures compared with WALK from 10 min until 30 min post-exercise (P ≤ 0.001; P ≤ 0.05) and over the entire recovery period (P < 0.001; P < 0.001). WALK had increased rectal temperature compared with HOSE (P < 0.001) but did not differ at any time (P > 0.10). GLUT recovery was faster with HOSE than with WALK (P = 0.001), but t_1/2 did not differ for PECT (P > 0.10). Rectal temperature was lower compared with GLUT through 10 min (P < 0.001) and PECT until 15 min post-exercise (P < 0.001). Hosing immediately post-exercise decreased middle gluteal and pectoral muscle temperatures. GLUT muscle recovery rate was improved with hosing, but PECT was not. Rectal temperature underestimated the change in GLUT and PECT muscle temperatures for at least 10 min post-exercise. These results indicate the benefits of PTSM over rectal temperature for repeated measurements specifically when placed in the GLUT muscle.

Springer, R.W., I.A. Robinson, E.D. Robyn, Z. Gillen, and J.D. Pagan. 2025. Effects of two cooling modalities on temperature recovery of rectal, middle gluteal muscle, and pectoral muscle temperatures. Journal of Equine Veterinary Science 148:15550.