Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison 53706.
USDA Dairy Forage Research Center, Marshfield, WI 54449.
J Dairy Sci. 2022 Mar;105(3):2201-2214. doi: 10.3168/jds.2020-19982. Epub 2022 Jan 5.
The objective of this study was to determine growth, feed intake, and feed efficiency of postbred dairy heifers with different genomic residual feed intake (RFI) predicted as a lactating cow when offered diets differing in energy density. Postbred Holstein heifers (n = 128, ages 14-20 mo) were blocked by initial weight (high, medium-high, medium-low, and low) with 32 heifers per block. Each weight block was sorted by RFI (high or low) to obtain 2 pens of heifers with high and low genomically predicted RFI within each block (8 heifers per pen). Low RFI heifers were expected to have greater feed efficiency than high RFI heifers. Dietary treatments consisted of a higher energy control diet based on corn silage and alfalfa haylage [HE; 62.7% total digestible nutrients, 11.8% crude protein, and 45.6% neutral detergent fiber; dry matter (DM) basis], and a lower energy diet diluted with straw (LE; 57.0% total digestible nutrients, 11.7% crude protein, and 50.1% neutral detergent fiber; DM basis). Each pen within a block was randomly allocated a diet treatment to obtain a 2 × 2 factorial arrangement (2 RFI levels and 2 dietary energy levels). Diets were offered in a 120-d trial. Dry matter intake by heifers was affected by diet (11.0 vs. 10.0 kg/d for HE and LE, respectively) but not by RFI or the interaction of RFI and diet. Daily gain was affected by the interaction of RFI and diet, with low RFI heifers gaining more than high RFI heifers when fed LE (0.94 vs. 0.85 kg/d for low and high RFI, respectively), but no difference for RFI groups when fed HE (1.16 vs. 1.19 kg/d for low and high RFI, respectively). Respective feed efficiencies were improved for low RFI compared with high RFI heifers when fed LE (10.6 vs. 11.8 kg of feed DM/kg of gain), but no effect of RFI was found when fed HE (9.4 vs. 9.5 kg of DM/kg of gain for high and low RFI, respectively). No effect of RFI or diet on first-lactation performance through 150 DIM was observed. Based on these results, the feed efficiency of heifers having different genomic RFI may be dependent on diet energy level, whereby low RFI heifers utilized the LE diet more efficiently. The higher fiber straw (LE) diet controlled intake and maintained more desirable heifer weight gains. This suggests that selection for improved RFI in lactating cows may improve feed efficiency in growing heifers when fed to meet growth goals of 0.9 to 1.0 kg of gain/d.
本研究旨在确定不同基因组残饲采食量（RFI）预测为泌乳牛时，不同能量密度日粮对后备奶牛生长、采食量和饲料效率的影响。选择荷斯坦后备奶牛（n = 128，年龄 14-20 月龄），按初始体重（高、中高、中低和低）进行分组，每组 32 头。根据 RFI（高或低）对每个体重组进行排序，以获得每个分组内具有高和低基因组预测 RFI 的 2 个栏位（每个栏位 8 头）。低 RFI 奶牛的饲料效率预计高于高 RFI 奶牛。日粮处理包括基于玉米青贮和苜蓿干草青贮的高能对照日粮（HE；总可消化养分 62.7%、粗蛋白 11.8%和中性洗涤纤维 45.6%；干物质基础）和用秸秆稀释的低能日粮（LE；总可消化养分 57.0%、粗蛋白 11.7%和中性洗涤纤维 50.1%；干物质基础）。每个栏位内的动物随机分配日粮处理，以获得 2×2 析因设计（2 个 RFI 水平和 2 个日粮能量水平）。日粮试验期为 120 天。奶牛的干物质采食量受日粮（HE 和 LE 分别为 11.0 和 10.0kg/d）影响，但不受 RFI 或 RFI 和日粮互作影响。日增重受 RFI 和日粮互作的影响，低 RFI 奶牛在采食 LE 时的日增重高于高 RFI 奶牛（分别为 0.94 和 0.85kg/d），但采食 HE 时两组无差异（分别为 1.16 和 1.19kg/d）。与采食高能日粮相比，采食低能日粮的低 RFI 奶牛的饲料效率更高（分别为 10.6 和 11.8kg 干物质采食量/kg 增重），但采食高能日粮时 RFI 无影响（高和低 RFI 分别为 9.4 和 9.5kg 干物质采食量/kg 增重）。在到 150 天泌乳期前，RFI 或日粮对奶牛首次泌乳性能无影响。基于这些结果，不同基因组 RFI 后备奶牛的饲料效率可能取决于日粮能量水平，低 RFI 奶牛对低能日粮（LE）的利用率更高。高纤维秸秆（LE）日粮控制了采食量，维持了更理想的奶牛增重。这表明，在泌乳牛中选择提高 RFI 可能会提高生长奶牛的饲料效率，当满足 0.9-1.0kg/d 的增重目标时。
