Sweating Losses of Urea, Sodium and Potassium in Barki Sheep Under the Environmental Stress of Semi-Arid Coastal Desert Conditions

Abstract

The present study was intended to investigate the effects of watering regimen, protein intake, housing environment and season on the potential losses of urea, sodium and potassium in the sweat of Barki sheep. Sweating rate, Na + , K + and urea concentration in sweat and serum, and sweat Na + , K + and urea output were determined in eight non-pregnant non-lactating Barki ewes fed at the maintenance energy level. Half of the animals were watered daily, whereas the other half was intermittently watered once every three days. There were two levels of protein intake, however, 100% and 50% of their estimated maintenance requirements. Moreover, half of the animals were kept outdoors and not sheltered whereas the other half was housed indoors. The experimental treatments were repeated three times between April and August to represent spring, early summer, and late summer seasons. The sweating rate in daily watered sheep was about 108 g/m 2 /h. The outdoor sheep had significantly higher sweat rates than those kept indoors. Also, the sweating rate of sheep in early and late summer was significantly higher than those in spring. Water deprivation and the level of protein intake did not significantly affect sweat rate. The urea excreted in sweat followed changes in sweat rate. Urea output increased in animals kept outdoors as compared to indoors and in summer as compared to spring. The sweat:serum urea concentration ratio was always less than one. The ratio ranged from 0.5 to 0.1 which possibly indicates passive diffusion of urea into the sweat. Sweat:serum concentration ratio ranged from 1.00 to 1.87 for sodium and from 149.7 to 224.5 for potassium for the different experimental treatments. Consequently, the sweat K + output was much greater than that of Na + even though its serum concentration was much less than Na +. The increase in K/Na ratio may suggest the presence of a Na + :K + exchange mechanism in the duct of the sweat gland similar to that in the distal tubule of the kidney. The present results gave evidence that losses of potassium, sodium and to some extent urea in sweat could be quantitatively significant affecting the nutritional and physiologic state of the desert animal and in particular the acid-base balance of blood and other body fluids. Quantitative assessment of such losses under different conditions of environmental stress would be essential in devising sound management systems.