Changes of the histochemical properties and meat quality traits of porcine muscles during growth. II) Effect of feed restriction in pigs slaughtered at the same body weight and varying age

Twenty-four Swiss Large White barrows from six litters (four pigs per litter) had either ad libitum (A) or restrictive (R) access to a grower and finisher diet from 20 to 60 and from 60 to 100 kg BW, respectively. Two littermates from both feeding regime were slaughtered at 61 (A60 and R60) or 101 kg BW (A100 and R100). The histochemical properties of myofibers as well as meat quality traits of the longissimus muscle (LM) and light portion of the semitendinosus (STL) were assessed. Muscle fibers were stained and classified based on the stain reaction as slow oxidative (SO), fast oxidative-glycolytic (FOG), and fast glycolytic (FG), and fiber area and distribution were determined. Myofiber size was not (P ≥ 0.11) affected by the dietary treatments. Regardless of the BW at slaughter, in the LM of R-pigs the relative amount of SO fibers was lower (P = 0.06) and that of FG fibers was higher (P < 0.01) compared with the LM of A-pigs. The SO fibres were more abundant in the STL of R60than A60-, A100-, and R100-pigs (feed restriction × BW interaction; P = 0.02). Compared to pigs of the A-group, the STL of R-pigs was less tender (P < 0.01) and percentages of cooking loss were higher (P = 0.02). In conclusion, at the same BW at slaughter, feed restriction did not impair the myofiber size. By contrast myofibers of the LM were more glycolytic in Rcompared with A-pigs suggesting a dietary impact on myofiber maturation. Although several quality traits were negatively affected by the feed restriction, they were unrelated to the myofiber characteristics as evidenced by the lacking significant correlation coefficients between meat quality traits and myofiber characteristics.