Paradis F, Yue S, Grant J R, Stothard P, Basarab J A, Fitzsimmons C
J Anim Sci. 2015 Jul;93(7):3331-41. doi: 10.2527/jas.2015-8975.
In beef cattle, production feedstuffs are the largest variable input cost. Beef cattle also have a large carbon footprint, raising concern about their environmental impact. Unfortunately, only a small proportion of dietary energy is directed toward protein deposition and muscle growth whereas the majority supports body maintenance. Improving feed efficiency would, therefore, have important consequences on productivity, profitability, and sustainability of the beef industry. Various measures of feed efficiency have been proposed to improve feed utilization, and currently, residual feed intake (RFI) is gaining popularity. However, the cost associated with measuring RFI and the limited knowledge of the biology underlying improved feed efficiency make its adoption prohibitive. Identifying molecular mechanisms explaining divergence in RFI in beef cattle would lead to the development of early detection methods for the selection of more efficient breeding stock. The objective of this study was to identify hepatic markers of metabolic feed efficiency in replacement beef heifers. A group of 87 heifers were tested for RFI adjusted for off-test backfat thickness (RFIfat). Preprandial liver biopsies were collected from 10 high- and 10 low-RFIfat heifers (7 Hereford–Aberdeen Angus and 3 Charolais–Red Angus–Main Anjou per group) and gene expression analysis was performed using RNA sequencing and quantitative real-time PCR. The heifers used in this study differed in RFIfat averaging 0.438 vs. –0.584 kg DM/d in high- and low-RFIfat groups, respectively. As expected, DMI was correlated with RFIfat and ADG did not differ between high- and low-RFIfat heifers. Through a combination of whole transcriptome and candidate gene analyses, we identified differentially expressed genes involved in inflammatory processes including hemoglobin β (HBB), myxovirus resistance 1 interferon-inducible protein p78 (MX1), ISG15 ubiquitin-like modifier (ISG15), hect domain and RLD 6 (HERC6), and interferon-induced protein 44 (IFI44) whose mRNA abundance was lower (HBB) or higher (MX1, ISG15, HERC6, and IFI44) in low-RFIfat heifers. These genes have been shown to be directly or indirectly modulated by interferon signaling and involved with innate immunity. Our results suggest that more efficient heifers respond differently to hepatic proinflammatory stimulus, potentially expending less energy toward combating systemic inflammation and redirecting nutrients toward growth and protein accretion.
在肉牛养殖中，生产饲料是最大的可变投入成本。肉牛的碳足迹也很大，这引发了人们对其环境影响的担忧。不幸的是，日粮能量中只有一小部分用于蛋白质沉积和肌肉生长，而大部分能量用于维持身体机能。因此，提高饲料效率将对肉牛产业的生产力、盈利能力和可持续性产生重要影响。人们已经提出了各种饲料效率衡量指标来提高饲料利用率，目前，剩余采食量（RFI）越来越受到关注。然而，测量RFI的成本以及对提高饲料效率背后生物学原理的了解有限，使得其应用受到限制。确定解释肉牛RFI差异的分子机制将有助于开发早期检测方法，以选择更高效的种畜。本研究的目的是确定后备肉牛小母牛代谢性饲料效率的肝脏标志物。对一组87头小母牛进行了根据测定结束时背膘厚度调整的RFI（RFIfat）测试。从10头高RFIfat和10头低RFIfat小母牛（每组7头赫里福德-阿伯丁安格斯牛和3头夏洛莱-红安格斯-曼安茹牛）采集空腹肝脏活检样本，并使用RNA测序和定量实时PCR进行基因表达分析。本研究中使用的小母牛RFIfat存在差异，高RFIfat组和低RFIfat组的平均RFIfat分别为0.438和–0.584千克干物质/天。正如预期的那样，干物质采食量与RFIfat相关，高RFIfat和低RFIfat小母牛之间的平均日增重没有差异。通过全转录组分析和候选基因分析相结合，我们鉴定出了参与炎症过程的差异表达基因，包括血红蛋白β（HBB）、抗黏液病毒1干扰素诱导蛋白p78（MX1）、ISG15泛素样修饰物（ISG15）、Hect结构域和RLD 6（HERC6）以及干扰素诱导蛋白44（IFI44），其mRNA丰度在低RFIfat小母牛中较低（HBB）或较高（MX1、ISG15、HERC6和IFI44）。这些基因已被证明直接或间接受到干扰素信号的调节，并与先天免疫有关。我们的结果表明，效率更高的小母牛对肝脏促炎刺激的反应不同，可能在对抗全身炎症方面消耗较少的能量，并将营养物质重新导向生长和蛋白质积累。
