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

Twenty-four Swiss Large White barrows from six litters were given either ad libitum (A) or restrictive (R) access to a grower diet from 21 to 60 kg body weight (BW). At d 113 of age six pigs of the A(BW = 62 kg) and six siblings of the R-group (BW = 51 kg) were slaughtered. The remaining 12 barrows were fed a finisher diet from 60 kg BW until slaughter. The day of slaughter barrows were 154 d old and the BW of the Aand R-group averaged 100 and 87 kg, respectively. 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. Regardless of the age at slaughter, pigs of the R-group had smaller (P ≤ 0.04) SO and FG fibers in the LM and STL, and smaller (P < 0.01) FOG fibers in the STL than their siblings of the A-group. The STL had more (P = 0.03) FOG and fewer (P = 0.04) FG fibers in pigs of the Rthan pigs of the A-group. The muscles of pigs in the R-group were less (P ≤ 0.03) tender and percentages of cooking loss were higher (P ≤ 0.08) than of pigs in the A-group. In conclusion, hypertrophy as well as differentiation of muscle fibers was affected by the restricted nutrient supply when pigs had the same age at slaughter. However, the extent of the dietary impact varied among muscles.