本试验旨在研究饲粮添加不同水平低聚木糖（XOS）对仔猪生长性能、背最长肌营养成分含量及肌纤维类型组成的影响，探讨XOS在仔猪饲粮中的最佳添加量及其对肌肉营养成分和肌纤维类型组成的调控作用。试验选取健康的21日龄"杜×长×大"断奶仔猪120头，随机分为4组，每组6个重复，每个重复5头猪。对照组饲喂基础饲粮，试验组（Ⅰ组、Ⅱ组和Ⅲ组）分别饲喂在基础饲粮中添加100、250和500 mg/kg XOS的饲粮，试验期为56 d。试验结束后，每重复选取1头接近平均体重的仔猪进行屠宰取样。结果表明：1）与对照组相比，Ⅰ组仔猪的平均日增重和平均日采食量显著增加（P<0.05），Ⅱ组和Ⅲ组平均日采食量显著增加（P<0.05），但末重和料重比各组之间差异不显著（P>0.05）；2）各组之间背最长肌粗蛋白质、粗脂肪以及游离氨基酸包括亮氨酸、甘氨酸及天冬氨酸含量差异不显著（P>0.05），其他氨基酸含量试验组与对照组相比均有不同程度地升高或降低；3）与对照组相比，Ⅰ组肌球蛋白重链（MyHC）Ⅱa和MyHC Ⅱx mRNA相对表达量显著增加（P<0.05），Ⅱ组MyHC Ⅰ mRNA相对表达量与Ⅲ组相比显著增加（P<0.05）；与对照组相比，Ⅰ组腺苷酸活化蛋白激酶α、沉默交配型信息调节因子2同源蛋白1和解偶联蛋白3 mRNA相对表达量显著增加（P<0.05），但过氧化物酶体增殖物激活受体γ辅激活因子1α mRNA相对表达量各组之间差异不显著（P>0.05）。由此可知，仔猪饲粮中合理添加XOS能提高生长性能，促进慢肌纤维相关基因的表达，推荐添加水平为100~250 mg/kg。

This experiment was conducted to study the effects of different xylooligosaccharide (XOS) supplemental levels on growth performance, longissimus dorsi muscle nutrient content and muscle fiber type composition of piglets, in order to determine the optimal dose of XOS supplemental level and the possible regulatory mechanisms of XOS for muscle nutrient and muscle fiber type composition. A total of 120 healthy weaned Duroc×Large White×Landrace piglets with 21 days of age were randomly assigned into 4 groups with 6 replicates per group and 5 piglets per replicate. Pigs in the control group were fed a basal diet and the others in the experimental groups (groups Ⅰ, Ⅱ and Ⅲ) were fed the basal diets supplemented with 100, 250 and 500 mg/kg XOS, respectively. The experiment lasted for 56 days. When the experiment was over, one pig per replicate close to the average weight was chosen to slaughter sampling. The results showed as follows: 1) compared with the control group, average daily gain and average daily feed intake (ADFI) of pigs in group Ⅰ were significantly increased (P<0.05), and ADFI of pigs in groups Ⅱ and Ⅲ was significantly increased (P<0.05), too. But there were no significant differences in the final weight and the ratio of feed to gain among all groups (P>0.05). 2) There were no significant differences in the contents of crude protein, ether extract, free amino acids such as leucine, glycine and aspartic acid among all groups (P>0.05), while the other amino acids in experimental groups rose or fell with different levels compared with the control group. 3) The myosin heavy chain (MyHC) Ⅱa and MyHC Ⅱx mRNA relative expression levels in group Ⅰ were significantly higher than those in the control group (P<0.05), and MyHC Ⅰ mRNA relative expression level in group Ⅱ was significantly increased compared with group Ⅲ (P<0.05). Compared with the control group, the mRNA relative expression levels of AMP-activated protein kinase alpha, silent mating type information regulation 2 homolog 1 and uncoupling protein 3 were significantly increased (P<0.05), and there were no significant differences in the mRNA relative expression level of peroxisome proliferator-activated receptor-γ coactivator-1α among all groups (P>0.05). In conclusion, the suitable XOS supplementation in piglet diet can improve the growth performance and promote the mRNA relative expression levels of genes related to slow-twitch muscle fiber, and the recommend supplemental level is 100 to 250 mg/kg under the present experiment.