Department of Animal Science, Texas A&M University, College Station, TX, 77845, USA.
STgenetics, Navasota, 77868 TX, USA.
J Anim Sci. 2024 Jan 3;102. doi: 10.1093/jas/skae289.
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 the 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 4 electronic feed bunks and 1 pen with a GreenFeed emissions 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 were collected at weighing. Phenotypic RFI (RFIp) was calculated as the residual from the 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 the 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 compared to high RFIg heifers (-0.196 vs 0.222 kg/d, respectively). Low RFIg heifers had 8.7% fewer (P < 0.05) bunk visit events per day and tended to have an 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 (DM) and nutrient digestibility did not differ (P > 0.05) between heifers with divergent RFIg. 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.
残留采食量（RFI）是饲料效率的一个指标，具有中等的遗传力，与体型和生产力无关，因此是作为提高生长牛饲料效率的选择标准进行研究的理想特征。本研究的目的是研究具有不同基因组增强选择价值的 RFI（RFIg）的荷斯坦小母牛在性能、饲料效率、采食行为、气体通量和养分消化率方面的差异。从 453 头商业荷斯坦小母牛的当代群体中选择具有低（n=29）或高（n=26）RFIg 的荷斯坦小母牛（n=55；BW=352±64kg）。小母牛在 2 个围栏之间轮换，每个围栏配备 4 个电子饲料槽和 1 个 GreenFeed 排放监测（GEM）系统。收集了 84 天的个体干物质采食量（DMI）和采食行为数据。每周测量体重（BW），称重时采集点粪便样本。表型 RFI（RFIp）的计算方法是从 DMI 对平均日增重（ADG）和中期代谢 BW（BW0.75）的回归中得出的残差。使用包括 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。具有不同 RFIg 的小母牛在 BW 和 ADG 方面没有差异（P>0.05）；然而，低 RFIg 小母牛每天消耗的饲料少 7.5%（P<0.05）。因此，与高 RFIg 小母牛相比，低 RFIg 小母牛表现出更有利的（P<0.05）RFIp（分别为-0.196 和 0.222kg/d）。低 RFIg 小母牛每天的饲料槽访问事件少 8.7%（P<0.05），并且采食速度慢 11.2%（P<0.10）。低 RFIg 小母牛的甲烷（CH4）排放量（g/d）低 7.7%（P<0.05），二氧化碳（CO2）产生量（g/d）低 6.1%（P≤0.05），产热量（Mcal/d）低 5.6%（P≤0.05）比高 RFIg 小母牛。然而，低 RFIg 和高 RFIg 小母牛的 CH4 产量和 CO2 产量（g/kg DMI）以及单位 DMI 的产热量（Mcal/kg DMI）没有差异（P>0.05）。具有不同 RFIg 的小母牛的干物质（DM）和养分消化率没有差异（P>0.05）。结果表明，基于 RFIg 的选择为选择具有有利饲料效率表型的牛提供了机会，以提高牛业的经济和环境可持续性。
