摘要
Residual feed intake (RFI) is a widely used measure of feed efficiency in cattle. Although the precise biologic mechanisms associated with improved feed efficiency are not well-known, most-efficient steers (i.e., with low RFI coefficient) downregulate abundance of proteins controlling protein degradation in skeletal muscle. Whether cellular mechanisms controlling protein turnover in ruminal tissue differ by RFI classification is unknown. The aim was to investigate associations between RFI and signaling through the mechanistic target of rapamycin (MTOR) and ubiquitin-proteasome pathways in ruminal epithelium. One hundred and forty-nine Red Angus cattle were allocated to 3 contemporary groups according to sex and herd origin. Animals were offered a finishing diet for 70 d to calculate the RFI coefficient for each. Within each group, the 2 most-efficient (n = 6) and least-efficient animals (n = 6) were selected. Compared with least-efficient animals, the most-efficient animals consumed less feed (P < 0.05; 18.36 vs. 23.39 kg/d DMI). At day 70, plasma samples were collected for insulin concentration analysis. Ruminal epithelium was collected immediately after slaughter to determine abundance and phosphorylation status of 29 proteins associated with MTOR, ubiquitin-proteasome, insulin signaling, and glucose and amino acid transport. Among the proteins involved in cellular protein synthesis, most-efficient animals had lower (P ≤ 0.05) abundance of MTOR, p-MTOR, RPS6KB1, EIF2A, EEF2K, AKT1, and RPS6KB1, whereas MAPK3 tended (P = 0.07) to be lower. In contrast, abundance of p-EEF2K, p-EEF2K:EEF2K, and p-EIF2A:EIF2A in most-efficient animals was greater (P ≤ 0.05). Among proteins catalyzing steps required for protein degradation, the abundance of UBA1, NEDD4, and STUB1 was lower (P ≤ 0.05) and MDM2 tended (P = 0.06) to be lower in most-efficient cattle. Plasma insulin and ruminal epithelium insulin signaling proteins did not differ (P > 0.05) between RFI groups. However, abundance of the insulin-responsive glucose transporter SLC2A4 and the amino acid transporters SLC1A3 and SLC1A5 also was lower (P ≤ 0.05) in most-efficient cattle. Overall, the data indicate that differences in signaling mechanisms controlling protein turnover and nutrient transport in ruminal epithelium are components of feed efficiency in beef cattle.
摘要译文
剩余饲料摄入量（RFI）是牛饲料效率的一种广泛使用的度量标准。尽管与提高饲料效率有关的精确生物学机制尚不为人所知，但最有效的ste牛皮（即具有低RFI系数）会下调控制骨骼肌蛋白质降解的蛋白质的丰度。尚不清楚通过RFI分类控制瘤胃组织中蛋白质更新的细胞机制是否不同。目的是研究雷帕霉素（MTOR）和瘤胃上皮中泛素-蛋白酶体途径的机制靶点，RFI和信号传导之间的关联。根据性别和牧群来源，将140头红安格斯牛分为3个当代群体。为动物提供70天的最终饮食，以计算每只动物的RFI系数。在每组中，选择了2个效率最高的动物（n = 6）和效率最低的动物（n = 6）。与效率最低的动物相比，效率最高的动物消耗的饲料更少（P <0.05； DMI为18.36 vs. 23.39 kg / d。在第70天，收集血浆样品用于胰岛素浓度分析。屠宰后立即收集瘤胃上皮，以确定与MTOR，泛素-蛋白酶体，胰岛素信号以及葡萄糖和氨基酸转运相关的29种蛋白质的丰度和磷酸化状态。在参与细胞蛋白质合成的蛋白质中，效率最高的动物的MTOR，p-MTOR，RPS6KB1，EIF2A，EEF2K，AKT1和RPS6KB1的丰度较低（P≤0.05），而MAPK3的丰度较低（P = 0.07）。 。相反，在效率最高的动物中，p-EEF2K，p-EEF2K：EEF2K和p-EIF2A：EIF2A的丰度更高（P≤0.05）。在最高效的牛中，在蛋白质降解所需的蛋白质催化步骤中，UBA1，NEDD4和STUB1的丰度较低（P≤0.05），而MDM2的丰度较低（P = 0.06）。 RFI组之间血浆胰岛素和瘤胃上皮胰岛素信号蛋白无差异（P> 0.05）。但是，在效率最高的牛中，胰岛素反应性葡萄糖转运蛋白SLC2A4以及氨基酸转运蛋白SLC1A3和SLC1A5的丰度也较低（P≤0.05）。总体而言，数据表明控制瘤胃上皮中蛋白质更新和营养运输的信号传导机制的差异是肉牛饲料效率的组成部分。
Ahmed A Elolimy[1];Emad Abdel-Hamied[1];Liangyu Hu[1];Joshua C McCann[1];Daniel W Shike[1];Juan J Loor[1]. RAPID COMMUNICATION: Residual feed intake in beef cattle is associated with differences in protein turnover and nutrient transporters in ruminal epithelium[J]. Journal of Animal Science, 2019,97(5): 2181-2187