This study determined the Pectoralis (P) major mixed muscle protein turnover (PT) in two meat broiler lines, Line A and Line B, during the finishing grow-out feeding period (21–42 days) as affected by the dietary metabolizable energy (ME) levels and ambient temperatures. Experimental finishing diets consisted of 80, 90, 100, 110 and 120% ME of recommended nutrient guidelines for energy level. Fractional synthesis rates (FSR) or fractional degradation rates (FDR) were measured in P. major at day 36 and 42. Protein and fat mass gain were measured, and respective energy retention efficiencies as protein and fat (EREp and EREf) were determined. Metabolic heat production (HP) was also reported. Experimental feeding studies were conducted in cool season (24 hr mean: 69.91˚F and 63.98% RH) and in hot season (24 hr mean: 77.55˚F and 86.04% RH). Results showed that FSR or FDR values were not affected by dietary ME levels at day 36, whereas reduced FSR (p < .05) were observed at day 42 fed diets with reduced ME levels (≤100% ME) which could have resulted from greater maintenance energy requirement of maturing broilers at that age. Broilers fed reduced ME diets (≤100% ME) maintained protein mass (equivalent to broilers fed ≥100%–120% ME) by reduced FDR and increased feed intake. Grow-out ambient temperature did not affect FSR or FDR values across ME levels. Line B retained higher protein mass, lower fat mass and greater HP compared to Line A. This was followed by higher feed intake in Line B. Further, Line B exhibited higher EREp and lower EREf across dietary ME levels. In summary, PT homeostasis and body composition changes in broiler lines studied seemed to be regulated by the birds’ intent to normalize energy intake as per physiological need by controlling feed intake.

中文翻译：

---

日粮能量水平对饲养在不同养成环境中的两个肉鸡品系胸大肌混合肌肉蛋白转换和身体成分的影响

本研究确定了在育成期（21-42 天）的两个肉鸡品系 A 和 B 系中胸大肌 (P) 主要混合肌肉蛋白转换 (PT) 受日粮代谢能的影响。 ME) 水平和环境温度。实验性肥育日粮由能量水平推荐营养指南的 80%、90%、100%、110% 和 120% ME 组成。部分合成率 (FSR) 或部分降解率 (FDR) 在P. major中测量在第 36 天和第 42 天。测量了蛋白质和脂肪质量的增加，并确定了作为蛋白质和脂肪（EREp 和 EREF）的各自能量保留效率。还报告了代谢产热 (HP)。在凉爽季节（24 小时平均值：69.91°F 和 63.98% RH）和炎热季节（24 小时平均值：77.55°F 和 86.04% RH）进行了实验喂养研究。结果表明，FSR 或 FDR 值不受第 36 天日粮 ME 水平的影响，而 FSR 降低（p < .05) 在第 42 天饲喂 ME 水平降低（≤ 100% ME）的日粮中观察到，这可能是由于成熟肉鸡在那个年龄需要更多的维持能量。通过降低 FDR 和增加采食量，饲喂减少 ME 日粮（≤100% ME）的肉鸡保持蛋白质质量（相当于饲喂≥100%–120% ME 的肉鸡）。养成环境温度不影响整个 ME 水平的 FSR 或 FDR 值。与线 A 相比，线 B 保留了更高的蛋白质质量、更低的脂肪量和更高的 HP。随后是线 B 更高的采食量。此外，线 B 在日粮 ME 水平上表现出更高的 EREp 和更低的 EREF。总之，所研究的肉鸡品系的 PT 稳态和身体成分变化似乎受鸡只意图通过控制采食量使能量摄入正常化以符合生理需要的意图来调节。