Rehydration fluid temperature affects voluntary drinking in horses dehydrated by furosemide administration and endurance exercise

To determine whether temperature of rehydration fluid influences voluntary rehydration by horses, six 2–3-year-old horses were dehydrated (4–5% body weight loss) by a combination of furosemide administration and 30 km of treadmill exercise. For the initial 5 min following exercise, horses were offered a 0.9% NaCl solution at 10, 20, or 30 °C. Subsequently, after washing and cooling out, voluntary intake of water at 10, 20, or 30 °C from 20 to 60 min after exercise was measured. Fluid intake (FI) during the first 5 min of recovery was 9.8±2.5, 12.3±2.1 and 9.7±2.0 L (p>0.05) for saline at 10, 20, and 30 °C, respectively. Although not a significant finding, horses offered 0.9% NaCl at 20 °C tended to take fewer (p=0.07), longer drinks than when saline at either 10 or 30 °C was offered. Between 20 and 60 min of recovery, intake of water at 20 °C (7.7±0.8 L) and 30 °C (6.6±1.2 L) was greater (p<0.05) than that at 10 °C (4.9±0.5 L). Thus, total FI was 14.7±2.5, 19.9±2.5, and 16.3±2.4 L for rehydration fluids at 10, 20, and 30 °C, respectively (p<0.05, value for 20 °C water greater than that for 10 °C water). Although the amount of metabolic heat transferred to the initial saline drink was correlated with the decrease in core temperature during the initial 5 min of recovery, heat transfer to ingested fluid was most likely responsible for the dissipation of, at most, 5% of the heat generated during endurance exercise. In conclusion, following exercise these dehydrated-normothermic horses voluntary drank the greatest amount of fluid at near ambient (20 °C) temperature. Although not determined in this study, greater satiation of thirst by oropharngeal cooling may have contributed to lesser intake of colder (10 °C) fluid.