ABSTRACT. Bama Xiang and Landrace pigs are the local fatty and lean breeds, respectively, in China. We compared differences in carcass traits, meat quality traits, and myosin heavy chain (MyHC) types in the longissimus dorsi muscles between Bama Xiang and Landrace pigs. This was done in pigs of the same age, using real-time PCR, to investigate the relationship between MyHC fiber types and carcass characteristics, meat quality traits, and the key factors regulating muscle fiber type. Bama Xiang pigs exhibited smaller size and slower growth than Landrace pigs (P < 0.01). We found that the superior meat quality, especially the high intramuscular fat (IMF) content in Bama Xiang pig, was related to elevated type I oxidative muscle fiber content (P < 0.01). In contrast, Landrace pig muscle had a higher glycolytic type IIb muscle fiber content (P < 0.01). MyHC I gene expression was significantly positively correlated with backfat thickness and IMF content (P < 0.01). MyHC IIb was significantly negatively correlated with IMF content (P < 0.05), and positively correlated with carcass yield (P < 0.05). AMP-activated protein kinase and peroxisome proliferatoractivated receptor-g coactivator-1a are suggested to be the two key factors regulating muscle fiber type in pigs. Our results indicate that muscle fiber composition is one of the key differences leading to the differences of meat quality between Bama Xiang and Landrace pigs. These results may provide a theoretical basis for further studies of the molecular mechanism underlying the excellent meat quality of the Bama Xiang pig.

Overt differences exist between Chinese local pigs and exotic pig breeds, especially in muscle growth rate and meat quality. However, the underlying molecular mechanisms remain unclear. This study aimed to assess muscle fibre types and metabolic enzymes in Bama miniature pigs and Landrace swine. Meat quality traits, including intramuscular fat content, and muscle colour, conductivity, and tenderness, were assessed in these pig breeds. Then, muscle fibre types were classified, and mRNA amounts and activities of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and malate dehydrogenase (MDH) assessed, in M. longissimus from the two pig breeds, at various ages. Our data showed significantly higher back fat thickness, muscle conductivity, and intramuscular fat content in samples from Bama miniature pigs compared with the values obtained for Landrace pigs (p < .05). In addition, SDH activity was significantly higher, and LDH activity overtly lower in Bama pigs compared with Landrace swine (p < .05). Furthermore, myosin heavy-chain (MyHC) II A, II B, and II X mRNA levels in Bama miniature pigs at 180 were significantly higher than values obtained for Landrace pigs of the same age. Although MyHC I gene expression levels were similar in Bama miniature and Landrace pigs at 180 days of age, significantly higher amounts were obtained in 300 day old Bama miniature pigs compared with 180 day old Landrace pigs (p < .05). Collectively, these preliminary findings indicated that skeletal muscles from Bama miniature pigs may contain more oxidative fibres compared with those from Landrace pigs, which might explain the meat quality differences between the two pig breeds.