J. Anim Sci.
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J. Anim Sci. 1975. 41:794-798.
© 1975 American Society of Animal Science
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Effect of Fascicular Arrangement on the Apparent Number of Myofibers in the Porcine Longissimus Muscle1

H. J. Swatland

University of Guelph2, Guelph, Ontario, Canada

Abstract

One complete longissimus muscle was removed from each of eight Yorkshire pigs (live weight 61 to 87 kg) and divided into 11 or more subunits following fascicular arrangement within the muscle. The number of myofibers appearing in transverse sections (apparent number) at the midlength of each subunit was estimated from the subunit midlength cross sectional area (CSA) and packing density (PD) of myofibers per unit area in frozen transverse histological sections from the subunit midlength. Myofibers were delineated by silver staining of endomysial sheaths. In chops taken at the level of the second lumbar vertebrae in intact sides, the apparent number of myofibers was estimated from the longissimus muscle CSA and myofiber PD in sections cut in a plane parallel to the face of the chop. The sum of the apparent numbers of myofibers in all subunits of each muscle (total apparent number) was only poorly related (r = .35, not significant) to the apparent number in anterior lumbar chops. Weight of the whole longissimus muscle was related to the anterior lumbar apparent number (r = .59, P<.01) but not to the total apparent number (r = .02). The implication of these results is that an increase in the real number of myofibers in the longissimus muscle achieved by selective breeding will not always or automatically cause an increase in the apparent number of myofibers in individual pork chops.

Footnotes

1 Research supported by the Ontario Ministry of Agriculture and Food, project number A-03-599.

2 Department of Animal and Poultry Science.






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Copyright © 1975 by the American Society of Animal Science.