ACUTE HEAT ACCLIMATION AND KIDNEY-FUNCTION IN BROILERS

Broilers previously exposed to high environmental temperatures (heat-a cclimated) are more resistant to heat stress and consume more water du ring heat stress than nonacclimated controls. Two experiments were con ducted to determine whether heat-acclimated broilers conserve body wat er by reducing urine and solute (Na) excretion. In the first experimen t, renal function studies were conducted at an ambient temperature (T( a)) of approximately 21 C using anesthetized 7-wk-old male broilers. C ontrol birds reared at a constant T(a) of 24 C (Group N: noncycled T(a )) were compared with birds that had been heat-acclimated by exposure for 3 to 6 d to a daily sinusoidal cycle of 24 to 35 to 24 C (Group C: cycled T(a)). In the second experiment, renal function studies were c onducted on anesthetized 5-wk-old control and heat-acclimated male bro ilers while they were exposed to a T(a) of 21 C (Ambient T(a): Groups NA, CA), or to a T(a) of 32 C (High T(a): Groups NH, CH). When high in travenous infusion rates (.37 mL/kg body mass per min) were used to si mulate the volume expansion caused by thermogenic polydipsia, urine fl ow rates were significantly lower in Groups C and CA than in Groups N and NA, osmolal clearances were lower in Groups CA and CH than in Grou ps NA and NH, and all heat-acclimated groups in both experiments (Grou ps C, CA, CH) had significantly lower glomerular filtration rates (GFR ), filtered loads of Na, and tubular Na reabsorption rates than the re spective control groups (Groups N, NA, NH). These changes in kidney fu nction potentially would minimize urinary fluid and solute loss when h eat-acclimated broilers consume large quantities of water to support e vaporative cooling. Reductions in GFR, filtered loads of Na, and tubul ar Na reabsorption rates also may help heat-acclimated broilers reduce the metabolic heat load associated with active (energy requiring) rec overy of solute (Na) from the glomerular ultrafiltrate.