The effects on sheep urinary and plasma electrolytes of 4 weeks' exposure to different ambient temperatures and humidities

Abstract

Urinary electrolyte output and plasma electrolyte concentration were determined in six Letelle wethers exposed to hot-humid, hot-dry, cool-humid and cool-dry environments. Urinary Na+ output increased during the first week of exposure to both hot environments, decreased after the third week of hot-humid exposure, and declined during the first 2 weeks of the cool-humid exposure. Changes in urinary Na+ output were accompanied by major changes in the opposite direction of urinary K+ and Cl- output. The changes in urinary electrolyte output were accompanied by lesser changes in plasma Na+, K+, and Cl- concentration. Increases in the temperature-humidity index were correlated with increased urine Na+ concentration, decreased urine K+ and Cl- concentration, decreased urine and plasma osmolality, decreased plasma Na+ concentration, and increased plasma Cl- concentration. Changes in urine volume, feed intake, total plasma protein concentration, and plasma cortisol were related to changes in urinary electrolyte output, especially after prolonged heat exposure. The results provide convincing evidence that changes in ambient temperature and humidity were related to major changes in urinary electrolyte output during the first weeks of exposure. More prolonged changes in ambient temperature and humidity were associated with major changes in urine output and feed intake which, in turn, were related to major changes in urinary electrolyte output and minor changes in plasma electrolyte concentration.