Department of Animal and Veterinary Science, University of Idaho, Moscow 83844.
J Anim Sci. 2013 Dec;91(12):5626-36. doi: 10.2527/jas.2013-6609. Epub 2013 Oct 1.
Investigating the genetic and physiological drivers of postweaning residual feed intake (RFI) and finishing phase feed efficiency (FE) may identify underlying mechanisms that are responsible for the variation in these complex FE traits. The objectives were 1) to evaluate the relationship of serum IGF-I concentration and muscle gene expression with postweaning RFI and sire maintenance energy (MEM) EPD and 2) to determine fiber type composition as it relates to postweaning RFI and finishing phase FE. Results indicate that RFI and serum IGF-I concentration were not associated (P > 0.05); however, negative correlations (P < 0.05) between sire MEM EPD and serum IGF-I concentration were observed. Gene expression differences between high- and low-RFI animals were observed in cohort 1, where IGFBP5 expression was greater (P < 0.05) in high-RFI animals. When animals were grouped according to sire MEM EPD, the low MEM EPD group of cohort 1 showed greater muscle mRNA expression (P < 0.01) of fatty acid synthase (FASN) and marginally (P < 0.10) greater expression of IGFBP5 and C/EBP alpha (C/EBPα) whereas the high MEM EPD group of cohort 2 had greater muscle mRNA expression of IGFBP2 (P < 0.05) and C/EBPα (P ≤ 0.01) and marginally (P < 0.10) greater expression of IGFBP3. Biopsy tissue samples collected at harvest revealed that the percentage of type IIa fibers was lower (P ≤ 0.05) in high-RFI steers, with a similar trend (P < 0.10) being observed in high finishing phase FE steers. The percentage of type IIb fibers was higher (P < 0.05) in high-RFI (and finishing phase FE) steers than in low-RFI (and finishing phase FE) steers. There was a marginal, negative correlation between RFI and type I (r = -0.36, P = 0.08) and IIa (r = -0.37, P = 0.07) fiber percentages and a positive correlation (r = 0.48, P = 0.01) between RFI and type IIb fiber percentage whereas finishing phase FE was negatively correlated (r = -0.43, P = 0.03) with type I fiber percentage and positively correlated (r = 0.44, P = 0.03) with type IIb fiber percentage. Therefore, our data indicate that 1) serum IGF-I (collected at weaning) is not an indicator of postweaning RFI, 2) the GH-IGF axis appears to have some involvement with RFI at the molecular level; however, muscle gene expression results were not consistent across cohorts, and 3) low-RFI animals may have the ability to more efficiently maintain and accrete muscle mass due to their fiber type composition, specifically a greater proportion of type I fibers.
研究断奶后剩余采食量（RFI）和育肥后期采食量（FE）的遗传和生理驱动因素，可以确定导致这些复杂 FE 性状变异的潜在机制。目的是 1）评估血清 IGF-I 浓度和肌肉基因表达与断奶后 RFI 和 sire 维持能量（MEM）EPD 的关系，2）确定纤维类型组成与断奶后 RFI 和育肥后期 FE 的关系。结果表明，RFI 和血清 IGF-I 浓度之间没有关联（P>0.05）；然而，观察到 sire MEM EPD 和血清 IGF-I 浓度之间存在负相关（P<0.05）。在第 1 个队列中观察到高 RFI 和低 RFI 动物之间的基因表达差异，其中 IGFBP5 的表达更高（P<0.05）。当根据 sire MEM EPD 对动物进行分组时，第 1 个队列的低 MEM EPD 组的肌肉 mRNA 表达（P<0.01）显示出更高的脂肪酸合成酶（FASN），并且 IGFBP5 和 C/EBPα（C/EBPα）的表达也有轻微增加（P<0.10），而第 2 个队列的高 MEM EPD 组的肌肉 mRNA 表达显示出更高的 IGFBP2（P<0.05）和 C/EBPα（P≤0.01），并且 IGFBP3 的表达也有轻微增加（P<0.10）。收获时采集的活检组织样本显示，高 RFI 牛的 IIa 型纤维百分比较低（P≤0.05），而高育肥后期 FE 牛也有类似的趋势（P<0.10）。高 RFI（和育肥后期 FE）牛的 IIb 型纤维百分比较高（P<0.05），低于低 RFI（和育肥后期 FE）牛。RFI 与 I 型（r=-0.36，P=0.08）和 IIa 型（r=-0.37，P=0.07）纤维百分比呈负相关，与 IIb 型纤维百分比呈正相关（r=0.48，P=0.01），而育肥后期 FE 与 I 型纤维百分比呈负相关（r=-0.43，P=0.03），与 IIb 型纤维百分比呈正相关（r=0.44，P=0.03）。因此，我们的数据表明 1）断奶时（收集）的血清 IGF-I 不是断奶后 RFI 的指标，2）GH-IGF 轴似乎在分子水平上与 RFI 有一定的关系；然而，各队列的肌肉基因表达结果并不一致，3）低 RFI 动物由于其纤维类型组成，可能具有更有效地维持和增加肌肉质量的能力，具体表现为更高比例的 I 型纤维。
