OBJECTIVE The aim of the present study was to investigate the effects of repeated thermal conditioning (RTC) at an early age on physiological and behavioral responses in chicks. METHODS Birds were assigned to one of the four treatments in which the RTC was exposure to 40 °C for 15 min daily. The treatments were 1) no thermal conditioning (control); 2) early exposure group (EE; RTC from 2 to 4 days of age); 3) later exposure group (LE; RTC from 5 to 7 days of age); or 4) both early and later exposure (BE; RTC from 2 to 7 days of age). All groups of chicks were challenged with high ambient temperature (40 °C for 15 min) at two weeks of age. RESULTS During heat challenge, initiation times of dissipation behaviors (panting and wing-drooping) were measured. Rectal temperature and respiration rate were measured after and before heat challenge. Hypothalamic samples and blood were collected at the end of heat challenges. Initiation times of dissipation behaviors and rectal temperature were not affected by the treatments. Increases in respiration rate in response to heat challenge were suppressed by early RTC treatment. There was no clear pattern of glucose levels in relation to thermal conditioning, whereas plasma corticosterone levels were decreased by early treatment (EE and BE groups). Hypothalamic thyrotropin releasing hormone gene expression was suppressed by early and later thermal conditioning and suppressed further by both early and later exposure. Neuropeptide Y gene expression in the BE group was lower than in the other groups, with a similar trend for corticotropin releasing hormone expression. CONCLUSION Our results suggest that the effect of repeated thermal conditioning on the central thermoregulatory system depends on the number of times that chicks experienced conditioning. In addition, repeated thermal conditioning has greater effects on the acquisition of thermotolerance when conditioning occurs in chicks of two to four days of age in comparison with chicks of five to seven days of age.

中文翻译：

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新生儿期反复的热调节会影响雏鸡对急性热应激的行为和生理反应

目的 本研究的目的是研究早期重复热调节 (RTC) 对雏鸡生理和行为反应的影响。方法 家禽被分配到四种处理中的一种，其中 RTC 每天暴露于 40 °C 15 分钟。处理是1)没有热调节(对照)；2）早期暴露组（EE；RTC 2-4日龄）；3）后期暴露组（LE；RTC 5-7日龄）；或 4) 早期和晚期暴露（BE；RTC 从 2 到 7 日龄）。在两周大的时候，所有组的小鸡都接受了高环境温度（40°C 持续 15 分钟）的攻击。结果 在热挑战期间，测量了耗散行为（气喘和翅膀下垂）的起始时间。在热刺激之前和之前测量直肠温度和呼吸率。在热激发结束时收集下丘脑样品和血液。耗散行为的起始时间和直肠温度不受治疗的影响。早期 RTC 治疗抑制了响应热挑战的呼吸率增加。没有与热调节相关的明确葡萄糖水平模式，而血浆皮质酮水平因早期治疗而降低（EE 和 BE 组）。下丘脑促甲状腺激素释放激素基因表达受到早期和后期热调节的抑制，并被早期和后期暴露进一步抑制。BE 组的神经肽 Y 基因表达低于其他组，促肾上腺皮质激素释放激素的表达趋势相似。结论 我们的结果表明，反复热调节对中央体温调节系统的影响取决于雏鸡经历调节的次数。此外，与 5 至 7 日龄的雏鸡相比，当 2 至 4 日龄的雏鸡进行调节时，反复进行热调节对获得耐热性的影响更大。