Muscle-fibre types in porcine longissimus muscle of different genotypes and their association with the status of energy metabolism

To study the difference in muscle-fibre types in porcine muscle among different genotypes and its association with energy metabolism, composition of myosin heavy chain (MyHC) mRNA and energy metabolism indices were determined in the longissimus muscle (LM). Pig breeds included Jinhua (JHP), Zhongbai (ZBP), Duroc x Zhongbai cross (DZP) and Duroc x Yorkshire x Landrace cross (DYL). JHP pigs were found to have the highest proportions of MyHC I, IIa and IIx mRNA (P < 0.05), creatine kinase (CK) activity (P < 0.05) and the lowest glycolytic potential (GP) compared with the other genotypes. The proportions of MyHC I and IIa mRNA increased in the order of DYL < DZP < ZBP < JHP, whereas the trend was opposite for MyHC IIb mRNA. The proportions of MyHC I, IIa and IIx mRNA were positively correlated with CK activity and the turnover ratio of creatine phosphate (CP) (P < 0.01), and negatively correlated with GP, glucose-6-phosphate (G-6-P) and lactate (LA) contents (P < 0.01), with the trends being opposite for MyHC IIb mRNA. The results indicate that muscle-fibre type in porcine LM is influenced by the genetic background of pigs. For example, JHP pigs had more of Types I, IIa and IIx fibres than did other genotypes. Proportions of Types I, IIa and IIx fibres were positively correlated with CK reaction (ATP-CP) capacity and negatively correlated with GP. These data provide some evidence for exploring the effective mechanism of muscle-fibre type on pork quality.