Shinder D, Rusal M, Tanny J, Druyan S, Yahav S
Institute of Animal Science, Volcani Center, Bet Dagan 50250, Israel.
Poult Sci. 2007 Oct;86(10):2200-9. doi: 10.1093/ps/86.10.2200.
The potential to induce improved thermotolerance in broiler chickens is of great importance. Thermal conditioning is one of the management tools used to improve thermotolerance, enabling broilers to cope with extreme environmental conditions. This study investigated the effects of exposing chicks to low ambient temperature (T(a)) on-chick body (T(b)), surface (T(s)) temperatures and total sensible heat loss (SHL) by convection and radiation from the body and from 2 main radiative organs, the face and the legs. At 3, 4, or at both 3 and 4 d of age, chicks were exposed to 5 degrees C for 1.5 h a day (to avoid mortality) or to 10 or 15 degrees C for 3 h a day. In general, in all treatments, the results during exposure to cold differed significantly from the control. A second cold exposure (on d 4 after a first exposure on d 3) clearly enhanced the chicks' ability to maintain on-chick body surface temperatures during exposure to 15 degrees C and to recover much faster from cold exposure. A dramatic decline in average surface temperature was observed during the first 15 min of chicks' exposure to the various low ambient temperatures in all ages, reaching the lowest values in the 5 degrees C treated chicks. The face responded immediately to cold exposure by significantly increasing its SHL to a level that then remained relatively steady (15 degrees C) or declined moderately with time (10 and 5 degrees C). In the legs, however, a significant and continuous decline in SHL was exhibited in all ages. The dynamics of SHL from the legs differed from that from the face, suggesting that the legs are a major organ for vasomotor responses, whereas the face is a more conservative vasoregulatory organ. It is concluded that repetitive exposure to cold may enhance thermotolerance, and that this is partially related to the vasomotor responses. This is the first report quantifying the differentiation between the legs as a responsive vasomotor organ and the face as a conservative vasomotor one.
诱导肉鸡提高耐热性的潜力具有重要意义。热适应是用于提高耐热性的管理手段之一，能使肉鸡应对极端环境条件。本研究调查了将雏鸡暴露于低环境温度（Ta）对雏鸡体温（Tb）、体表温度（Ts）以及通过对流和辐射从身体及两个主要辐射器官（面部和腿部）散失的总显热损失（SHL）的影响。在3日龄、4日龄或3日龄和4日龄时，雏鸡每天暴露于5℃ 1.5小时（以避免死亡）或每天暴露于10℃或15℃ 3小时。总体而言，在所有处理中，冷暴露期间的结果与对照组有显著差异。第二次冷暴露（在3日龄首次暴露后于4日龄进行）明显增强了雏鸡在暴露于15℃时维持雏鸡体表温度的能力，并且从冷暴露中恢复得更快。在所有年龄段的雏鸡暴露于各种低环境温度的最初15分钟内，观察到平均体表温度急剧下降，在5℃处理的雏鸡中降至最低值。面部通过显著增加其显热损失对冷暴露立即做出反应，该水平随后保持相对稳定（15℃）或随时间适度下降（10℃和5℃）。然而，在腿部，所有年龄段的显热损失均呈现显著且持续的下降。腿部显热损失的动态变化与面部不同，这表明腿部是血管运动反应的主要器官，而面部是更保守的血管调节器官。得出的结论是，反复暴露于寒冷可能会增强耐热性，且这部分与血管运动反应有关。这是第一份量化作为反应性血管运动器官的腿部与作为保守性血管运动器官的面部之间差异的报告。
