Wideman R F, Ford B C, May J D, Lott B D
Department of Poultry Science, Pennsylvania State University, University Park 16802.
Poult Sci. 1994 Jan;73(1):75-88. doi: 10.3382/ps.0730075.
Broilers previously exposed to high environmental temperatures (heat-acclimated) are more resistant to heat stress and consume more water during heat stress than nonacclimated controls. Two experiments were conducted to determine whether heat-acclimated broilers conserve body water by reducing urine and solute (Na) excretion. In the first experiment, renal function studies were conducted at an ambient temperature (Ta) of approximately 21 C using anesthetized 7-wk-old male broilers. Control birds reared at a constant Ta of 24 C (Group N: noncycled Ta) 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 Ta). In the second experiment, renal function studies were conducted on anesthetized 5-wk-old control and heat-acclimated male broilers while they were exposed to a Ta of 21 C (Ambient Ta: Groups NA, CA), or to a Ta of 32 C (High Ta: Groups NH, CH). When high intravenous infusion rates (.37 mL/kg body mass per min) were used to simulate the volume expansion caused by thermogenic polydipsia, urine flow 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 Groups NA and NH, and all heat-acclimated groups in both experiments (Groups C, CA, CH) had significantly lower glomerular filtration rates (GFR), filtered loads of Na, and tubular Na reabsorption rates than the respective control groups (Groups N, NA, NH). These changes in kidney function potentially would minimize urinary fluid and solute loss when heat-acclimated broilers consume large quantities of water to support evaporative cooling. Reductions in GFR, filtered loads of Na, and tubular Na reabsorption rates also may help heat-acclimated broilers reduce the metabolic heat load associated with active (energy requiring) recovery of solute (Na) from the glomerular ultrafiltrate.
先前暴露于高温环境（热适应）的肉鸡比未适应的对照组更耐热，且在热应激期间消耗更多的水。进行了两项实验，以确定热适应的肉鸡是否通过减少尿液和溶质（钠）排泄来保存体内水分。在第一个实验中，使用麻醉的7周龄雄性肉鸡在约21℃的环境温度（Ta）下进行肾功能研究。将饲养在24℃恒定Ta下的对照鸡（N组：非循环Ta）与通过暴露于24至35至24℃的每日正弦循环3至6天进行热适应的鸡（C组：循环Ta）进行比较。在第二个实验中，对麻醉的5周龄对照和热适应雄性肉鸡进行肾功能研究，同时将它们暴露于21℃的Ta（环境Ta：NA组、CA组）或32℃的Ta（高温Ta：NH组、CH组）。当使用高静脉输注速率（每分钟0.37 mL/kg体重）来模拟由产热多饮引起的容量扩张时，C组和CA组的尿流率显著低于N组和NA组，CA组和CH组的渗透清除率低于NA组和NH组，并且两个实验中的所有热适应组（C组、CA组、CH组）的肾小球滤过率（GFR）、钠滤过负荷和肾小管钠重吸收率均显著低于各自的对照组（N组、NA组、NH组）。当热适应的肉鸡消耗大量水分以支持蒸发散热时，这些肾功能变化可能会使尿液中的液体和溶质损失最小化。GFR、钠滤过负荷和肾小管钠重吸收率的降低也可能有助于热适应的肉鸡降低与从肾小球超滤液中主动（耗能）回收溶质（钠）相关的代谢热负荷。
