Abstract:
The effects of short term heat exposure on the changes of body fluid and renal function were studied in four heifer buffaloes weighing between 174-207 kg. The animals were individually exposed to the sun up to 8 h each day over period of ten days (nonshaded period). Before this, they were kept in normal ambient temperature (control period). Each animal was fed same diet throughout experimental periods. In short term heat exposure, nonshaded buffaloes increased body water turnover rate while the marked decreases in total body water and blood volume were noted. On the first five days, there was initial increase in plasma volume with the decrease in total body water. On the tenth day of measurement, there were decreases in both plasma and blood volume. Short term heat exposed buffaloes showed increases in plasma concentrations of glucose, protein, urea and creatinine. During heat exposure, nonshaded buffaloes showed no significant changes of both GFR and E-RPF. On day ten of heat exposure, the increase in the rate of urine flow was coincided with increases of osmolar clearance, renal excretion of K[superscript +] and urine pH. Plasma chloride concentration significantly increased on the tenth day of heat exposure. The renal excretion of Pi and Cl[superscript -] decreased throughout nonshaded period while that of Na[superscript +] increased in the first five day and fell down thereadter. It can be concluded that during heat exposure, the change in body fluid distribution is drawn into two phases of response for evaporative cooling. The first phase occurred within the first five days which was characterized by mobilization of cellular water. A second phase of response occurred on the tenth day of measurement indicated the main loss of plasma water. The increases in plasma constituents during heat exposure would augment to maintain extracellular water during animals exposed to hot environment. The renal function studies suggested that on the first five days of heat exposure, the maintenance of extracellular fluid was regulated in part by Na[superscript +] loss from the kidney. On the tenth day of heat exposure, the animals let to the state of dehydration which was consistent to increase in renal Na[superscript +] retention. The renal behavior of electrolyte excretion particularly K[superscript +] in the tenth day nonshaded buffaloes was due to acid-base regulation during respiratory alkalosis.
