Renal function of sheep in hot environments

Abstract

The renal functions of adult Merino and crossbred sheep have been measured throughout the year in Brisbane (lat. 27° S.), and during acute and chronic exposure to hot environments (temperature 43°C dry bulb, 36°C wet bulb). In summer, glomerular filtration reached twice the rate found in winter and it rose during 2-9 weeks' exposure to heat. There was no change of glomerular filtration during 4 hours' acute heating at 43-44°C dry bulb (36-37°C wet bulb). Renal plasma flow, estimated by p-aminohippurate clearance, showed no variation with season, nor with exposures to heat. The mean tubular maximum of secretion of p-aminohippurate (TmPAH) of individual sheep ranged from 70 to 110 mg/min (2.1-2.6 mg/kg/min). These values are nearly twice those reported for other species. Some sheep showed depression of the TmPAH on long exposure to heat.