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Proliferation of Myofibrils in the Porcine Longissimus Muscle¹

University of Guelph², Guelph, Ontario, Canada

Abstract

Midlumbar samples were taken from longissimus muscles of Yorkshire pigs (16 Animals, live weights 24 to 139 kg) and the mean number of myofibrils per myofiber was estimated from data on the mean cross sectional area of myofibers and the mean packing density of myofibrils per unit area. Myofibrils were identified as non-reacting sites when the sarcoplasm was stained by the periodic acid-Schiff reactioin for glycogen in frozen transverse muscle sections. In red myofibers reacting strongly for DPNH-TR (diphosphopyridine nucleotide tetrazolium reductase) the mean number of myofibrils per myofiber increased at a rate of 11.5/kg live weight gain and myofibrillar number was closely related (r = .90) to live weight. In white myofibers reacting weakly for DPNH-TR the mean number of myofibrils per myofiber was less closely related to live weight (r = .66). Early attainment of a large number of myofibrils in white myofibers of some smaller animals made calculation of a rate of proliferatiion impossible. The maximum mean number of myofibrils per myofiber (2,180) was attained in red myofibers of the heaviest animal. There was no evidence of an increase in mean cross sectional dimensions of myofibrils.

¹ Research supported by the Ontario Ministry of Agriculture and Food and by a grant from the National Research Council of Canada.

² Department of Animal and Poultry Science.