Muscle Fiber Type, Rigor Development and Bone Strength in Double Muscled Cattle

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Abstract
Fifteen 13- to 15-month-old Angus bulls were classified by phenotype into three groups: double muscled, normal phenotype half-sibs of double muscled and normal phenotype controls unrelated to the other two groups. Biochemical and physiological properties of skeletal muscle and bone were studied on samples collected at slaughter or 48 hr. postmortem. Double muscled cattle were trimmer and heavier muscled as indicated by rib-eye area and fat thickness measurements and physical separation and chemical analysis of the 9-10-11th rib section. They had significantlylarger biceps femoris and semi-membranosusmuscles per 100 kg of carcass weight than either the half-sib or control groups. Lung, liver and hide weights were lower and dressing percent was higher (P <.05) in the double muscled bulls. Histologically, no degenerativechanges were found in any skeletal muscles examined. Both the biceps femoris and semitendinosus muscles of double muscled animals had a slightly higher percentage of white fibers and fewer red fibers (NADH- tetrazolium reductase) than control or half-sib bulls. Myosin ATPase staining demonstrated fewer β fibers and more α fibers in double muscled skeletal muscles. In addition, the β fibers and the α fibers which reacted very strongly tended to be smaller diameter while the α fibers with an intermediate reaction were slightly larger in the muscles of double muscled bulls. These data, when compared to previous research, indicate that muscle enlargement in double muscled cattle is probably due to a higher proportion of white fibers, hypertrophy of part of the white fiber population and the presence of more muscle fibers. There were no significant differences in initial extensibility, extensibility at rigor onset, extensibility at rigor completion or time to completion of rigor. Double muscled bulls had shorter metacarpals (P<.05) which tended to be lighter and have thinner cortices. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.

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