Histological characteristics of musculus longissimus dorsi and their correlation with restriction fragment length polymorphism of the myogenin gene in Jinghua × Pietrain F2 crossbred pigs

PCR-RFLP, periodic acid Schiff (PAS) and myosin heavy chain (MHC) immunohistochemistry were employed to survey the relationships between the genotypes of the myogenin gene (myog) and the histological characteristics of the muscle and other postmortem traits in the Jinghua × Pietrain (JP) F2 crossbred pigs. The muscle fibers were classified into three groups according to their PAS-reactivity: PAS(−), PAS(+∼++), and PAS(+++) and accounted for approximately 16%, 74% and 10% of the total muscle, respectively. MHC immunohistochemistry was used to categorize muscle fibers into either slow or fast fibers; the proportions of slow and fast fibers were 6% and 94%, respectively. Two different cleavage patterns and three genotypes (AA, AB and BB) were identified and their frequencies were 0.4087, 0.4986 and 0.0928, respectively, for the three genotypes and 0.6580 and 0.3420, respectively, for cleavage patterns A and B. Different genotypes were variably associated with cross-sectional area (p = 0.074), water-holding capacity (p = 0.002), pH (p < 0.001) and carcass temperature (p < 0.001) of the loin muscle. Different genotypes showed marked correlation with the L value (p < 0.001), a value (p = 0.002), and b (p < 0.001) of the Minolta meat color index. The genotypes were also significantly related to the cross-sectional area (p < 0.001), diameter (p < 0.001), aspect ratio (p < 0.001) and the density (p < 0.001) of muscle fibers from the longissimus dorsi muscle. The results also revealed that the genotypes showed no significant association with the circularity (p = 0.132) or the percentage of intramuscular connective tissue (p = 0.193).