饲养方式对苏尼特羊肌纤维组成和肉品质的影响及其调控机理

本实验以不同饲养方式下（放牧和舍饲）苏尼特羊背最长肌为材料，分析其肉品质指标的差异性，并利用ATPase染色法和实时荧光定量聚合酶链式反应技术对肌纤维类型进行划分，同时对相关代谢酶活力以及肌纤维转化相关调控基因mRNA表达量进行分析。结果表明，放牧组的胴体质量、L*值、剪切力和pH24值显著低于舍饲组（P＜0.05或P＜0.01）；IIB型肌纤维数量比例和面积比例，I型、IIA型和IIB型肌纤维直径和肌纤维横截面积，乳酸脱氢酶酶活力均显著低于舍饲组（P＜0.05或P＜0.01）。而放牧组IIA型肌纤维的数量比例和面积比例、MyHC I和MyHC IIX mRNA表达量、苹果酸脱氢酶和琥珀酸脱氢酶活力、AMPKα2和COX IV mRNA相对表达量显著高于舍饲组（P＜0.05或P＜0.01）。PGC-1α mRNA表达量在两种饲养方式下差异不显著（P＞0.05）。综上所述，与舍饲相比，放牧饲养能提高肌纤维的AMPKα2 mRNA相对表达量，激活位于线粒体内膜上的细胞色素c氧化酶IV，提高肌肉的线粒体生物合成水平，增强肌肉的氧化代谢能力，使肌纤维类型由酵解型向氧化型转化，进而改善肉品品质。

Effect of Feeding Regimens on Muscle Fiber Type Composition and Meat Quality of Sunit Sheep and Underlying Regulatory Mechanism

The effects of feeding regimens (pasture and confinement) on meat quality, muscle fiber type composition and key factors regulating muscle fiber type in the Longissimus dorsi muscle of Sunit sheep were investigated. The results showed that carcass mass (P < 0.05)，L* value (P < 0.05), Warner-Bratzler shear force (WBSF) (P < 0.05), pH24 (P < 0.01), the number and area proportion of type IIB muscle fiber (P < 0.01), the diameter of type I, IIA and IIB (P < 0.01), the cross-sectional area of type I (P < 0.05), IIA (P < 0.01) and IIB (P < 0.01), and lactic dehydrogenase (LDH) activity (P < 0.01) in the pasture group were significantly lower than those in the confinement group. However, the number and area proportion of type IIA muscle fiber (P < 0.01), the mRNA expression of the MyHC I and MyHC IIX genes (P < 0.01), the activity of malate dehydrogenase (MDH) and succinate dehydrogenase (SDH) (P < 0.05), and the mRNA expression of the AMPKα2 and COX IV genes (P < 0.05 or 0.01) were significantly higher in the pasture group than those in the confinement group. The mRNA expression of the PGC-1α gene was no significantly different between the two groups (P > 0.05). Overall, the present study indicated that compared to confinement feeding, pasture feeding could augment the relative mRNA expression level of AMPKα2 in the muscle and activate cytochrome c oxidase IV (COX IV) in the mitochondrial inner membrane, thus promoting mitochondrial biogenesis, enhancing oxidative metabolism, inducing the transition of muscle fiber types from glycolyzed to oxidized types, and finally improving meat quality.