The Effects of Anabolic Agents and Breed on the Fibers of the Longissimus Muscle of Male Cattle

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Abstract
Sample of longissimus muscle were taken from carcasses of steers, steers implanted with anabolic agents and bulls of Friesian and Charolais × Friesian breeds of cattle. Percent and mean cross-sectional areas (CSA) of three myofiber types (βR, αR and αW) were determined. The percentage of βR myofibers did not vary significantly with treatment. The implanted steers had 26% more αR and 8% less αW myofibers than the untreated steers, while the bulls had 33% more αR and 20% less αW myofibers than the implanted steers (P<.001). In the implanted steers the mean CSA of the βR myofibers was significantly greater than that of the untreated steers, but did not differ from that of the bull. The mean CSA of the αR myofibers increased considerably with treament, but only that of the bull was significantly greater than that of the untreated steers. The mean CSA of the αW myofibers in the implanted steers was identical with that of the untreated steers and significantly smaller than that of the bulls. In comparison to the untreated steers, signficant hypertrophy of all three myofiber types occurred in bulls. These findings demonstrate a significant increase in the oxidative capacity of the longissimus when the levels of both endogenous and exogenous anabolic agents are increased. They are also consistent with the greater efficiency of deposition of protein obtained with implanted steers and bulls. A significant breed difference was observed in the percentages of βR, αR and αW myofibers, and in the sizes of the βR and αR myofibers. No evidence of myofiber abnormality was found in any of the samples examined. Copyright © 1986. American Society of Animal Science . Copyright 1986 by American Society of Animal Science.

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