Haskell Agricultural Laboratory, Department of Animal Science, University of Nebraska, 57905 866 Road, Concord, NE 68728, USA.
Int J Biometeorol. 2010 Nov;54(6):629-35. doi: 10.1007/s00484-009-0229-0. Epub 2009 Apr 30.
Angus crossbred yearling steers (n = 168) were used to evaluate effects on performance and tympanic temperature (TT) of feeding additional potassium and sodium to steers exposed to excessive heat load (maximum daily ambient temperature exceeded 32°C for three consecutive days) during seasonal summer conditions. Steers were assigned one of four treatments: (1) control; (2) potassium supplemented (diet containing 2.10% KHCO₃); (3) sodium supplemented (diet containing 1.10% NaCl); or (4) potassium and sodium supplemented (diet containing 2.10% KHCO₃ and 1.10% NaCl). Overall, additional KHCO₃ at the 2% level or NaCl at the 1% level did not improve performance or heat stress tolerance with these diet formulations. However, the addition of KHCO₃ did enhance water intake. Independent of treatment effects, TT of cattle displaying high, moderate, or low levels of stress suggest that cattle that do not adequately cool down at night are prone to achieving greater body temperatures during a subsequent hot day. Cattle that are prone to get hot but can cool at night can keep average tympanic temperatures at or near those of cattle that tend to consistently maintain lower peak and mean body temperatures. In addition, during cooler and moderately hot periods, cattle change TT in a stair-step or incremental pattern, while under hot conditions, average TT of group-fed cattle moves in conjunction with ambient conditions, indicating that thermoregulatory mechanisms are at or near maximum physiological capacity.
Angus 杂交周岁阉牛（n = 168）用于评估在季节性夏季条件下，暴露于过度热负荷（连续三天最高日环境温度超过 32°C）的牛额外补充钾和钠对性能和鼓室温度（TT）的影响。牛被分配到以下四种处理之一：（1）对照组；（2）补充钾（饮食中含有 2.10% KHCO₃）；（3）补充钠（饮食中含有 1.10% NaCl）；或（4）补充钾和钠（饮食中含有 2.10% KHCO₃ 和 1.10% NaCl）。总体而言，在这些日粮配方中，2%水平的额外 KHCO₃或 1%水平的 NaCl 并没有提高性能或耐热性。然而，添加 KHCO₃确实增加了水的摄入量。独立于处理效果，表现出高、中或低应激水平的牛的 TT 表明，那些在夜间不能充分降温的牛在随后的炎热天气中更容易达到更高的体温。那些容易变热但夜间可以冷却的牛可以使平均鼓室温度保持在或接近那些倾向于持续保持较低峰值和平均体温的牛的温度。此外，在较凉爽和中度炎热时期，牛的 TT 呈阶梯式或递增模式变化，而在炎热条件下，群饲牛的平均 TT 与环境条件一起移动，表明体温调节机制处于或接近最大生理能力。
