Residual feed intake (RFI), a metric of feed efficiency, is moderately heritable and independent of body size and productivity, making it an ideal trait for investigation as a selection criterion to improve feed efficiency of growing cattle. The objective of this study was to examine the differences in performance, feed efficiency, feeding behavior, gas flux, and nutrient digestibility in Holstein heifers with divergent genomically enhanced breeding values for RFI (RFIg). Holstein heifers (n = 55; BW = 352 ± 64 kg) with low (n = 29) or high (n = 26) RFIg were selected from a contemporary group of 453 commercial Holstein heifers. Heifers were rotated between 1 of 2 pens, each equipped with four electronic feed bunks and one pen with a GreenFeed gaseous exchange monitoring (GEM) system. Individual dry matter intake (DMI) and feeding behavior data were collected for 84-d. Body weight (BW) was measured weekly and spot fecal samples collected at weighing. Phenotypic RFI (RFIp) was calculated as the residual from regression of DMI on average daily gain (ADG) and mid-test metabolic BW (BW0.75). A mixed model including the fixed effect of RFIg classification and random effect of group was used to evaluate the effect of RFIg classification on response variables. There were no differences (P > 0.05) in BW and ADG for heifers with divergent RFIg; however, low RFIg heifers consumed 7.5% less (P < 0.05) feed per day. Consequently, low RFIg heifers exhibited a more favorable (P < 0.05) RFIp (-0.196 vs 0.222 kg/d, respectively). Low RFIg heifers had 8.7% fewer (P < 0.05) bunk visit (BV) events per day and tended to have a 11.2% slower (P < 0.10) eating rate. Low RFIg heifers had 7.7% lower (P < 0.05) methane (CH4) emissions (g/d), 6.1% lower (P ≤ 0.05) carbon dioxide (CO2) production (g/d), and 5.6% lower (P ≤ 0.05) heat production (Mcal/d) than high RFIg heifers. However, CH4 yield and CO2 yield (g/kg DMI), and heat production per unit DMI (Mcal/kg DMI) did not differ (P > 0.05) between heifers with divergent RFIg. Dry matter and nutrient digestibility did not differ (P > 0.05) between heifers with divergent RFIg. Overall, heifers selected to be more feed efficient exhibited more favorable energy efficiencies and feed efficiency phenotypes. Results suggest that selection based on RFIg provides opportunities to select cattle with favorable feed efficiency phenotypes to increase the economic and environmental sustainability of the cattle industry.

中文翻译：

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基因组增强的残余采食量与生长荷斯坦小母牛的性能、饲料效率、采食行为、气体通量和营养消化率的关联


残余采食量 （RFI） 是衡量饲料效率的指标，具有中等遗传性，与体型和生产力无关，使其成为研究的理想性状，作为提高生长牛饲料效率的选择标准。本研究的目的是检查荷斯坦小母牛在性能、饲料效率、摄食行为、气体通量和营养消化率方面的差异，这些小母牛的 RFI （RFIg） 基因组增强育种值不同。荷斯坦小母牛 （n = 55;BW = 352 ± 64 kg） 具有低 （n = 29） 或高 （n = 26） RFIg 是从 453 头商业荷斯坦小母牛的当代组中选出的。小母牛在 2 个围栏中的 1 个之间轮换，每个围栏配备 4 个电子饲喂槽和 1 个带有 GreenFeed 气体交换监测 （GEM） 系统的围栏。收集 84-d 的个体干物质摄入量 （DMI） 和摄食行为数据。每周测量体重 （BW），并在称重时收集粪便样本。表型 RFI （RFIp） 计算为 DMI 对平均日增重 （ADG） 和中期代谢 BW （BW0.75） 的回归残差。采用包括 RFIg 分类固定效应和组随机效应的混合模型来评估 RFIg 分类对响应变量的影响。RFIg 不同的小母牛的 BW 和 ADG 没有差异 （P > 0.05）;然而，低 RFIg 小母牛每天消耗的饲料减少 7.5% （P < 0.05）。因此，低 RFIg 小母牛表现出更有利的 （P < 0.05） RFIp（分别为 -0.196 和 0.222 kg/d）。低 RFIg 小母牛每天的卧铺访问 （BV） 事件减少 8.7% （P < 0.05），进食率往往较慢 （P < 0.10）。低 RFIg 小母牛的甲烷 （CH4） 排放量 （g/d） 降低了 7.7% （P < 0.05），降低了 6.1% （P ≤ 0.05） 二氧化碳 （CO2） 产量 （g/d），与高 RFIg 小母牛相比，产热 （Mcal/d） 降低 5.6% （P ≤ 0.05）。然而，在RFIg不同的小母牛之间，CH4产量和CO2产量（g/kg DMI）和每单位DMI的产热（Mcal/kg DMI）没有差异（P > 0.05）。干物质和养分消化率在 RFIg 不同的小母牛之间没有差异 （P > 0.05）。总体而言，选择饲料效率更高的小母牛表现出更有利的能源效率和饲料效率表型。结果表明，基于 RFIg 的选择为选择具有良好饲料效率表型的牛提供了机会，以提高养牛业的经济和环境可持续性。