A Comparison of Five Cooling Methods in Hot and Humid Environments in Thoroughbred Horses.

Horses need aggressive cooling to prevent exertional heat illness after strenuous exercise in hot and humid conditions. This study compared various methods for cooling horses in such conditions, testing the hypothesis that continual application of running water would be the most effective method to decrease core temperature. Five Thoroughbreds were exercised on a treadmill at wet-bulb globe temperature of 31.8 ± 0.1°C until their pulmonary artery temperature reached 42°C. The time until the pulmonary artery temperature returned to <39°C (t39) and the rectal temperature at 30 minutes after the onset of cooling were compared between five cooling methods in a 5 × 5 Latin square design: walking, with no additional cooling (CONT); walking, with fans producing an air current of 3.0 m/s (FAN); walking, with the intermittent application of cold water (10°C) either with scraping (ICW + SCRAPE) or without scraping (ICW); and stationary, with the continuous tap water (26°C) application via shower hoses (STW). The STW produced the shortest t39 (P < .001). With intermittent cold water, ICW + SCRAPE tended to produce longer t39 than ICW (P = .06), and both produced significantly shorter t39 than FAN and CONT (P < .001). The t39 of the FAN tended to be shorter than with the CONT (P = .06). All the cooling methods resulted in lower rectal temperatures at 30 minutes than CONT. The temperature was the lowest with the shower method, with no significant differences between the fan and intermittent cold-water methods. Showering with tap water was the most effective method to decrease core temperature in horses.