Validation of Different Cooling Methods in Exercising Two-Year-Old Thoroughbred Racehorses Using Percutaneous Thermal-Sensing Microchips

Several post-exercise cooling methods have been debated, including hosing only the neck versus the whole body, removing water via scraping after water application, and using misters on mechanical walkers. However, no validation for these different cooling methods has been described. Use of percutaneous thermal-sensing microchips (PTSM) has allowed for repeated measurement of body temperature after exercise for determination of cooling rates. Thus, the study objective was to compare the cooling rate of the middle gluteal muscle (GLUT) undergoing different cooling modalities post-exercise using PTSM. Seven 2-year-old Thoroughbred racehorses were used in three 2-week crossover designs. Each phase compared 2 cooling treatments after completing a standardized exercise test on the racetrack. In phase 1 horses walked for 10 min and then were hosed for 5 min (HOSE) or walked under misters on a mechanical walker for 15 min (MIST). During phase 2, horses were walked for 10 min and then were either hosed over the whole body (WHOLE) or only the neck (NECK) for 5 min. In phase 3, horses were walked for 10 min and hosed for 5 min, then either had water removed from the body by scraping (SCRAPE) or remained wet with water dripping (CONTROL). Horses were placed into box stalls with fans from 15 min until 60 min post-exercise. GLUT temperatures, heart rate, and respiration rate were collected every 5 min until 60 min post-exercise. Changes in GLUT temperature from pre-exercise were used to determine logarithmic rates of heat dissipation and expressed as cooling half-life (t_1/2) in GraphPad Prism (v10.4.1). Data were further analyzed using R Statistical Program (v4.4.0) using an ANOVA with results (mean ± SEM) considered significant at P ≤ 0.05. Ambient temperature and relative humidity (mean ± SD) were 29.8 ± 1.4°C and 74.1 ± 7.2% across the study. In phase 1, HOSE t_1/2 (10.4 ± 2.5 min) did not differ from MIST (14.0 ± 2.5 min; P > 0.1). During phase 2, NECK (17.4 ± 2.4 min) had a greater t_1/2 than WHOLE (11.0 ± 2.4 min; P = 0.01). CONTROL (11.4 ± 1.9 min) and SCRAPE (10.6 ± 1.9 min; P > 0.1) did not differ for t_1/2 in phase 3. Heart rate was decreased in WHOLE versus NECK (P < 0.05), but no other treatments differed (P > 0.1). No treatments differed for respiration rate (P > 0.1). Overall, water application over the entire body of the horse enhances cooling rate whether applied over a short or extended period, while removal of water from the body by scraping does not affect cooling after exercise. More so, PTSM in the GLUT muscle allow for determination of cooling efficacy rather than using heart rate or respiration rate.

Pagan, J.D., M.S. Todd, S.M. Esposito, S. Dezalak, and R.W. Springer. 2025. Validation of different cooling methods in exercising two-year-old Thoroughbred racehorses using percutaneous thermal-sensing microchips. Journal of Equine Veterinary Science 148:105537.