Comparison of different skeletal muscles from growing domestic pigs and wild boars

The domestication process of pigs was associated with substantial morphological and physiological changes. The aim of this study was to comparatively investigate muscle microstructure and biochemical properties of four different skeletal muscles (M. longissimus, M. semitendinosus, M. psoas major, M. rhomboideus) in growing domestic pigs (n=5) and wild boars (n=4). The superiority of domestic pigs in body and muscle growth at three months of age was reflected by a 4-fold body weight and higher absolute weights of heart, liver and muscles. Relative muscle weights of M. psoas major and M. rhomboideus were reduced, whereas a 1.6-fold heavier M. semitendinosus was observed in domestic pigs compared with wild boars. In addition, the muscle cross-sectional area was greater in all muscles of domestic pigs resulting from about 3-fold fibre cross-sectional area, whereas total fibre number remained unchanged. As a consequence of intensified fibre hypertrophy, the fibre area per capillary is higher in all muscles of domestic pigs. Thus, the impaired supply with oxygen and nutrients may be one reason for the shift to the glycolytic muscle metabolism as indicated by a greater proportion of fast-twitch glycolytic fibres at the expense of fast-twitch oxidative fibres. This is also reflected by a higher ratio of lactate dehydrogenase to isocitrate dehydrogenase activity. Our data suggest that the intensified muscle growth was realized by myofibre hypertrophy at unchanged myofibre number in growing domestic pigs. It seems that domestication-induced changes were most pronounced in M. semitendinosus as the exterior ham muscle which may be related to muscle specific selection for lean growth.