The growth of three fiber types in beef longissimus muscle as influenced by breed and age

Guenther, J.J.; Novotny, K.K.; Hintz, R.L.

Animal Science Research Report, Agricultural Experiment Station, Oklahoma State University (MP-108): 51-53


Accession: 001009479

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Changes in the areas of alpha -white, alpha -red and beta -red fibres from the longissimus dorsi muscles of Aberdeen-Angus and Charolais calves slaughtered at 25, 240 and 650 days of age were determined. At 25 days, all 3 fibre types from the Angus calves were markedly larger than those from the Charolais. This size difference was maintained throughout the growing period. For the alpha -white fibres, however, the breed difference lessened with increased age. In the Angus, the beta -red fibres were slightly larger at 25 days than the alpha -reds; as the growing period was extended, the alpha -reds became significantly larger than the beta -reds. These findings may explain how the musculature of beef animals maintains its increased energy need during growth. There was a progressive percentage increase in fibre area with age; alpha -reds showed a greater increase than other types in both breeds. The alpha -white fibres of the Charolais had a greater net increase per day compared with the Angus, suggesting a faster overall muscle growth rate for the former breed. During the latter part of the growth phase (240-650 days), the beta -red fibres of the Angus enlarged at a significantly faster rate per day than those of the Charolais; this could be related to the capacity of the Angus to "marble".