The current study aimed to evaluate the effects of embryonic thermal manipulation (TM) on hatching criteria, chick quality, and subsequent growth performance of broiler chickens under heat stress (HS) condition. Two thousand fertile eggs were randomly divided between 2 groups and incubated under standard (37.8 °C and 56% relative humidity (RH)) and TM (39.5 °C and 65% RH) conditions. Temperature and humidity were identical in both groups within the first 10 days. The eggs in the TM group were exposed to 39.5 °C and 65% RH for 3 h/day from 11 to 16 days of incubation. Egg weight (EW) was measured in 1, 11, and 18 days of incubation, and eggshell temperature (EST) was recorded daily. Chick quality was, also, evaluated according to the Tona method on hatch day. Samples of the chicks (n = 20) were euthanized and dissected at 0-day post-hatch, and different carcass parts were weighed, and blood samples were collected for hormones analysis. The post-hatch growth performance of both groups was also recorded under HS (37 °C for 5 h beginning at 22 days) condition. The results showed that TM did not significantly affect hatchability and embryonic mortality (P > 0.05). The female chick percentage was higher in the TM group (P < 0.05). Eggshell temperature and serum concentrations of corticosterone and T4 were significantly higher in the TM compared with the control chicks (P < 0.05). The chick length was considerably shorter in TM chicks (P < 0.05). Chick quality was not influenced by TM. There was no significant difference between the two groups in the post-hatch growth performance (P > 0.05). In conclusion, exposing broiler embryos to the controlled TM did not have adverse effects on chick quality and post-hatch growth performance.

中文翻译：

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肉鸡胚胎反复热操作对孵化率、雏鸡质量和孵化后性能的影响

目前的研究旨在评估胚胎热操作 (TM) 对热应激 (HS) 条件下肉鸡的孵化标准、雏鸡质量和后续生长性能的影响。2000 个受精卵随机分为两组，在标准（37.8°C 和 56% 相对湿度 (RH)）和 TM（39.5°C 和 65% RH）条件下孵化。在前 10 天内，两组的温度和湿度相同。TM 组中的鸡蛋在孵化 11 至 16 天期间暴露于 39.5 °C 和 65% RH 3 小时/天。在孵化的第 1、11 和 18 天测量蛋重 (EW)，每天记录蛋壳温度 (EST)。雏鸡质量也在孵化日根据 Tona 方法进行评估。雏鸡样本 (n = 20) 在孵化后 0 天被安乐死并解剖，称重不同胴体部位，采集血样进行激素分析。在 HS（从 22 天开始，37°C 持续 5 小时）条件下也记录了两组的孵化后生长性能。结果表明，TM 对孵化率和胚胎死亡率没有显着影响（P > 0.05）。TM 组的雌性雏鸡百分比较高（P < 0.05）。与对照小鸡相比，TM 中蛋壳温度和血清皮质酮和 T4 浓度显着更高（P < 0.05）。TM 雏鸡的雏鸡长度明显较短（P < 0.05）。鸡的质量不受 TM 的影响。两组孵化后生长性能无显着差异（P > 0.05）。综上所述，