Evaluation of washing with cold water to facilitate heat dissipation in horses exercised in hot, humid conditions

OBJECTIVE: To determine whether body temperature of horses exercised in hot, humid conditions and then repetitively washed with cold water will decrease more rapidly than that of horses that are not washed, and to determine whether washing with cold water has deleterious effects on horses. ANIMALS: 5 physically fit Thoroughbred mares, 3 to 10 years old. PROCEDURES: Horses were exercised on a high-speed treadmill in hot (31.1+/-0.3 C), humid (relative humidity, 77.7+/-2%) conditions. Exercise was terminated when pulmonary artery temperature reached 41.5 C. Values for pulmonary artery, rectal, and left gluteal muscle temperatures were compared throughout a 30-minute recovery period after exercise during which horses stood quietly (passive cooling) or were cooled (active cooling) by repeated applications of cold (1 5.6+/-0.6 C) water. RESULTS: Pulmonary artery temperature was significantly less for actively cooled horses, compared with passively cooled horses 4 minutes into the recovery period. Left gluteal muscle temperature decreased significantly in actively cooled, but not passively cooled, horses during the recovery period. Heart rate and rectal temperature were significantly less for actively cooled horses by 15 minutes of the recovery period. Cooling technique did not effect hydration status, muscle health, or serum electrolyte concentrations. Active cooling did not cause obvious adverse effects. CONCLUSION AND CLINICAL RELEVANCE: Active cooling by washing with cold water is a safe, effective means for facilitating heat dissipation of horses after exercise in a hot, humid environment.