The objective of this study was to evaluate the relationship between muscle mitochondrial function and residual feed intake (RFI) in growing beef cattle. A 56-day feeding trial was conducted with 81 Angus × Hereford steers (initial BW = 378 ± 43 kg) from the University of California Sierra Foothills Research Station (Browns Valley, CA, USA). All steers were individually fed the same finishing ration (metabolizable energy = 3.28 Mcal/kg DM). Average daily gain (ADG), DM intake (DMI) and RFI were 1.82 ± 0.27, 8.89 ± 1.06 and 0.00 ± 0.55 kg/day, respectively. After the feeding trial, the steers were categorized into high, medium and low RFI groups. Low RFI steers consumed 13.6% less DM (P < 0.05) and had a 14.1% higher G : F ratio (P < 0.05) than the high RFI group. No differences between RFI groups were found in age, ADG or BW (P > 0.10). The most extreme individuals from the low and high RFI groups were selected to assess mitochondrial function (n = 5 low RFI and n = 6 high RFI). Mitochondrial respiration was measured using an oxygraph (Hansatech Instruments Ltd., Norfolk, UK). State 3 and State 4 respiration rates were similar between both groups (P > 0.10). Respiratory control ratios (RCRs, i.e., State 3 : State 4 oxygen uptakes) declined with animal age and were greater in low RFI steers (4.90) as compared to high RFI steers (4.26) when adjusted for age by analysis of covariance (P = 0.003). Mitochondrial complex II activity levels per gram of muscle were 42% greater in low RFI steers than in high RFI steers (P = 0.004). These data suggest that skeletal muscle mitochondria have greater reserve respiratory capacity and show greater coupling between respiration and phosphorylation in low RFI than in high RFI steers.

中文翻译：

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残余采食量不同的阉牛肌肉中的线粒体丰度和功能。

本研究的目的是评估生长肉牛的肌肉线粒体功能和剩余采食量 (RFI) 之间的关系。对来自加利福尼亚大学 Sierra Foothills 研究站（美国加利福尼亚州布朗斯谷）的 81 头 Angus × Hereford 公牛（初始体重 = 378 ± 43 kg）进行了为期 56 天的饲养试验。所有公牛单独饲喂相同的精加工日粮（代谢能 = 3.28 Mcal/kg DM）。平均日增重 (ADG)、干物质摄入量 (DMI) 和 RFI 分别为 1.82 ± 0.27、8.89 ± 1.06 和 0.00 ± 0.55 kg/天。饲喂试验后，公牛被分为高、中、低 RFI 组。与高 RFI 组相比，低 RFI 转向消耗 13.6% 的 DM (P < 0.05) 和高 14.1% 的 G: F 比 (P < 0.05)。RFI 组之间在年龄、ADG 或 BW 方面没有发现差异（P > 0.10）。选择来自低和高 RFI 组的最极端个体来评估线粒体功能（n = 5 低 RFI 和 n = 6 高 RFI）。使用血氧仪（Hansatech Instruments Ltd.，Norfolk，UK）测量线粒体呼吸。两组的状态 3 和状态 4 呼吸率相似（P > 0.10）。呼吸控制比率（RCR，即状态 3：状态 4 的摄氧量）随着动物年龄的增长而下降，并且在通过协方差分析调整年龄时，低 RFI 阉牛（4.90）与高 RFI 阉牛（4.26）相比更大（P = 0.003)。每克肌肉的线粒体复合物 II 活性水平在低 RFI 阉牛中比在高 RFI 阉牛中高 42% (P = 0.004)。