Cellular patterns of post-mortem glycogenolysis in longissimus dorsi muscles of pigs at different live weights

Serial frozen sections of longissimus dorsi muscles from twelve Canadian Yorkshire breed pigs at different live weights (13-86 kg) were stained for glycogen by the periodic acid-Schiff (PAS) reaction and reacted for NAD tetrazolium reductase to determine the mitochondrial content of muscle fibres. Sections from muscles taken immediately post mortem and at 5 hr post mortem were compared and the patterns of glycogenolysis in high, intermediate and low mitochondrial content fibres were assessed on the basis of the percentage of initially PAS-positive fibres which became PAS-negative 5 hr post mortem. This form of assessment was necessary because not all fibres were PAS-positive immediately post mortem. In smaller pigs, only a few muscle fibres depleted their stainable glycogen by 5 hr and most of these fibres had a high mitochondrial content. In larger pigs, most or all initially PAS-positive fibres became PAS-negative 5 hr post mortem. Fibres with a low mitochondrial content accounted for most of the glycogenolysis detected histochemically in larger animals. The overall percentage of PAS-positive fibres was related to glycogen concentration (mg/g), r = 0.52, P less than 0.025, when samples with all PAS-positive fibres were excluded.