Improving feed efficiency is crucial to the animal industry. Residual feed intake (RFI) is now regarded as an index of feed efficiency evaluation and is independent of growth characteristics. Our study aims to explore the alterations in growth performance and nutrient digestion in Hu sheep with different RFI phenotypes. Sixty-four male Hu sheep (body weight = 24.39 ± 1.12 kg; postnatal days = 90 ± 7.9) were selected for the study. After an evaluation period of 56 days and power analysis, samples were collected from 14 low RFI (L-RFI group, power = 0.95) and 14 high RFI sheep (H-RFI group, power = 0.95). The L-RFI sheep yielded a lower (P < 0.05) feed conversion ratio and dry matter intake; however, both groups exhibited similar average daily gain (P > 0.05). The acid detergent fiber, neutral detergent fiber, organic matter, and crude protein apparent digestibility were higher (P < 0.05) in L-RFI sheep. N intake and fecal N output (% of N intake) were lower (P < 0.05) and N retention (% of N intake) was higher (P < 0.05) in L-RFI sheep, whereas no difference (P > 0.05) was found in urine N output (% of N intake) between the 2 groups. Furthermore, L-RFI sheep gave lower (P < 0.05) serum glucose concentrations and higher (P < 0.05) non-esterified fatty acid concentrations. Meanwhile, a lower ruminal acetate molar proportion (P < 0.05) and higher propionate molar proportion (P < 0.05) were observed in L-RFI sheep. In summary, these results revealed that despite having lower dry matter intake, L-RFI sheep possess higher nutrient digestibility, N retention, ruminal propionate production and serum glucose utilization, in order to meet energy demands. Selection for low RFI sheep could reduce feed costs, which in turn provides economic benefits to the sheep industry.

提高饲料效率对畜牧业至关重要。剩余采食量（RFI）现在被视为饲料效率评价指标，与生长特性无关。本研究旨在探讨不同RFI表型湖羊生长性能和营养消化的变化。选择 64 只雄性湖羊（体重 = 24.39 ± 1.12 kg；产后天数 = 90 ± 7.9）进行研究。经过 56 天的评估期和功效分析后，从 14 只低 RFI（L-RFI 组，功效 = 0.95）和 14 只高 RFI 绵羊（H-RFI 组，功效 = 0.95）收集样本。 L-RFI绵羊的饲料转化率和干物质摄入量较低（P < 0.05）；然而，两组都表现出相似的平均日增重（P > 0.05)。 L-RFI绵羊的酸性洗涤纤维、中性洗涤纤维、有机质和粗蛋白表观消化率均较高（P < 0.05）。L-RFI 绵羊的 N 摄入量和粪便 N 排出量（占 N 摄入量的百分比）较低（P  < 0.05），N 保留（占 N 摄入量的百分比）较高（P  < 0.05），而无差异（P  > 0.05）在两组之间的尿 N 输出（N 摄入量的百分比）中发现。此外，L-RFI 绵羊的血清葡萄糖浓度较低 ( P < 0.05)， 非酯化脂肪酸浓度 较高 ( P < 0.05)。同时，较低的瘤胃乙酸盐摩尔比例（P  < 0.05）和较高的丙酸盐摩尔比例（P < 0.05) 在 L-RFI 绵羊中观察到。总之，这些结果表明，尽管干物质摄入量较低，但 L-RFI 绵羊具有较高的营养消化率、N 保留率、瘤胃丙酸产量和血糖利用率，以满足能量需求。选择低 RFI 羊可以降低饲料成本，从而为养羊业带来经济效益。