Influence of genetic selection on the myofibre type composition of porcine biceps femoris muscle: a comparative study of a purebred (Nero di Parma) and commercial hybrid pigs (Large White × Landrace × Duroc)

This study is aimed to evaluate histological features related to the different quality of meat cuts obtained from different pig breeds. We compared animals genetically selected to restore the original local purebred “Nero di Parma” pig, and highly selected fast-growing commercial hybrids. As weight is the main factor determining the time of slaughter, we compared equally weighing animals, sampled from slaughter for edible use, regardless of their age and sex, and immunohistochemically demonstrated the myofibre type composition of their biceps femoris muscle. In both groups we observed type I myofibres, situated as central islets, encircled by type IIA, IIX and IIB myofibres ordered in concentric rings according to the dynamic of their differentiation/maturation. However, the purebred pig muscles contained a smaller quantity of myofibres expressing the MyHC-IIb isoform, related to rapid postmortem glycolytic rate, meat toughness and poorer quality, in comparison to commercial hybrids. This proves that the latter are subjected to a more rapid transition in the expression of the different MyHC, probably as a consequence of genetic selection and breeding conditions, such as different feeding and housing reducing the possibility of continuous physical exercise. Further studies on the postnatal transitions timing of myosin heavy chain isoforms in functionally different muscles of various breeds are necessary to verify if they might be “artificially modulated”, with the aim to design breeding programs allowing a good balance between growth performance, muscularity and meat quality.