本试验旨在研究低聚木糖（XOS）对生长肥育猪血浆生化参数、肌肉氨基酸含量和肌纤维类型组成的影响。试验选取70日龄、平均体重约为30 kg的杜×长×大三元杂交猪80头，随机分为8组，每组10个重复（公母各占1/2），每个重复1头猪。试验设对照组、抗生素组、30~65 kg阶段100、250和500 g/t XOS组以及30~100 kg阶段100、250和500 g/t XOS组。于试猪平均体重达100 kg时，前腔静脉采血，离心分离血浆，测定生化参数；屠宰后取背最长肌样品，测定其氨基酸含量及肌纤维类型和肌肉生长相关基因mRNA表达量。结果表明：1）与对照组或抗生素组相比，饲粮添加不同剂量XOS可显著提高血浆球蛋白含量（P<0.05），显著降低白蛋白/球蛋白值（P<0.05）；2）与对照组或抗生素组相比，30~65 kg阶段饲粮添加250 g/t XOS可显著降低背最长肌中苏氨酸（Thr）、亮氨酸（Leu）、苯丙氨酸和丝氨酸（Ser）含量（P<0.05），30~65 kg阶段饲粮添加500 g/t XOS可显著增加背最长肌肌球蛋白重链Ⅱx（MyHCⅡx）、生肌决定因子（MyoD）、肌细胞生成素（MyoG）和生肌增强因子2A（MEF2A）mRNA表达量（P<0.05）；3）与对照组或抗生素组相比，30~100 kg阶段饲粮添加100或500 g/t XOS可显著增加背最长肌中Thr、Leu、Ser、总氨基酸、必需氨基酸和鲜味氨基酸含量以及MyHCⅡx、MyoD、MyoG、MEF2A和肌肉生长抑制素mRNA表达量（P<0.05）。综上所述，饲粮添加一定剂量的XOS可调控机体氮代谢，上调肌纤维类型和肌肉生长相关基因的表达，且以30~100 kg阶段添加100 g/t XOS的效果较佳。

The present study was conducted to investigate the effects of xylo-oligosaccharide (XOS) on plasma biochemical indices, amino acid contents and fiber type composition of muscle of growing-finishing pigs. A total of 80 Duroc×Large White×Landrace pigs with an initial body weight of about 30 kg and at 70 days of age were randomly assigned to 8 groups with 10 replicates per group (half male and half female) and one pig in a replicate. The eight groups included control group, antibiotic group, supplementation groups of 100, 250 and 500 g/t XOS during 30 to 65 kg stage, and supplementation groups of 100, 250 and 500 g/t XOS during 30 to 100 kg stage. When the average body weight of pigs reached about 100 kg, blood samples were collected by precaval vein, and then the plasma were obtained for analyzing biochemical indices. The samples of longissimus dorsi (LD) muscle were collected and the contents of amino acids, mRNA expression levels of muscle fiber types and muscle growth-related genes were measured. The results showed as follows:1) compared with the control group or antibiotic group, dietary supplementation with different doses of XOS significantly increased plasma globulin content and significantly decreased the ratio of albumin to globulin (P<0.05); 2) compared with the control group or antibiotic group, during 30 to 65 kg stage, dietary supplementation with 250 g/t XOS significantly decreased the contents of threonine (Thr), leucine (Leu), phenylalanine and serine (Ser) in LD muscle (P<0.05), and dietary supplementation with 500 g/t XOS significantly increased the mRNA expression levels of myosin heavy chain Ⅱx (MyHCⅡx), myogenic determination factor (MyoD), myogenin (MyoG) and muscle cell enhancement factor 2A (MEF2A) in LD muscle (P<0.05); 3) compared with the control group or antibiotic group, during 30 to 100 kg stage, dietary supplementation with 100 or 500 g/t XOS significantly increased the contents of Thr, Leu, Ser, total amino acids, essential amino acids and flavor amino acids, as well as the mRNA expression levels of MyHCIⅡx, MyoD, MyoG, MEF2A and myostatin in LD muscle (P<0.05). Collectively, these findings suggest that dietary supplementation with suitable doses of XOS can regulate nitrogen metabolism and up-regulate the expression levels of muscle fiber type and muscle growth-related genes, and the efficiency of dietary supplementation with 100 g/t XOS is optimal for pigs with 30 to 100 kg body weight.