Genetic improvement of muscle and meat quantity and quality of broiler chicken over the last 50 yr played a key role in broiler meat production. Thermal manipulation technique has been suggested to promote muscle growth and development. The combination of incubating temperature and timing or duration is very critical to determine the optimum protocol of thermal manipulation which underlines muscle growth improvement. Therefore, this study was to elucidate the optimum timing of thermal manipulation (TM) during embryogenesis on broiler pectoral and thigh muscle growth by assessing muscle growth parameter. This was achieved by analyzing the molecular expression levels of muscle insulin-like growth factor-1 (IGF-1), growth hormone (GH) and atrogin-1 during embryogenesis and d 35 post-hatch in addition to the measurement of sarcomeres length at d 35 post-hatch. One thousand, four hundred forty fertile eggs were randomly divided and equally into 5 groups. A control (no TM) and 4 thermal manipulated groups TM1, TM2, TM3, and TM4 that thermally subjected to 39°C for 18 h with 65% relative humidity daily during embryonic days (ED) ED7-11, ED 11-15, ED 15-18, and ED 7-18, respectively. IGF-1 and GH expression from early thermal manipulated chicks (ED7-11) were significantly higher in both pectoral and thigh muscles when compared to the control (P < 0.05). This improvement was in parallel with significant improvement in sarcomeres length of the same TM group on post-hatch d 35 (P < 0.05). On the other hand, Atrogin-1 expression was significantly lower in all treatment groups during post-hatch d 35 compared to the control (P < 0.05) (P < 0.05). It can be concluded that TM1 during ED 7-11 leads to improved pectoral and thigh muscles development without adversely affecting their performance. In addition, molecular and ultrastructure investigation of broiler chicken muscles can be used to predict meat quality and may be beneficial for commercial breeders to enhance broiler chicken growth and productivity.

过去 50 年来肉鸡肌肉和肉质数量和质量的遗传改良在肉鸡生产中发挥了关键作用。有人建议使用热操纵技术来促进肌肉生长和发育。孵化温度和时间或持续时间的组合对于确定强调肌肉生长改善的热操作的最佳方案非常关键。因此，本研究旨在通过评估肌肉生长参数来阐明胚胎发育过程中热操作(TM)对肉鸡胸肌和大腿肌肉生长的最佳时机。这是通过分析肌肉胰岛素样生长因子-1 (IGF-1)、生长激素(GH)的分子表达水平来实现的和 atrogin-1 在胚胎发生和孵化后 35 天，以及在孵化后 35 天测量肌节长度。将一千四百四十个受精卵随机分成5组。对照（无TM）和图4个的热操纵组TM1，TM2，TM3，和TM4该热在胚胎天每天进行39℃18小时65％相对湿度（ED）ED7-11，ED 11-15分别为 ED 15-18 和 ED 7-18。与对照组相比，早期热操纵雏鸡（ED7-11）的IGF-1和GH在胸肌和大腿肌肉中的表达显着升高（P <0.05）。这种改善与孵化后第 35 天同一 TM 组肌节长度的显着改善平行（P< 0.05)。另一方面，在孵化后第 35 天，所有处理组的 Atrogin-1 表达均显着低于对照组（P < 0.05）（P < 0.05）。可以得出结论，ED 7-11 期间的 TM1 可以改善胸肌和大腿肌肉的发育，而不会对其表现产生不利影响。此外，肉鸡肌肉的分子和超微结构研究可用于预测肉质，并可能有利于商业育种者提高肉鸡的生长和生产力。