J. Anim Sci.
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J. Anim Sci. 1986. 63:83-91.
© 1986 American Society of Animal Science
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The Effects of Anabolic Agents and Breed on the Fibers of the Longissimus Muscle of Male Cattle

M. J. Clancy, Janet M. Lester and J. F. Roche1

The Agricultural Institute, Animal Production Research Centre, Dunsinea, Castleknock, Dublin 15 and Grange, Dunsany, Co. Meath, Ireland

Abstract

Sample of longissimus muscle were taken from carcasses of steers, steers implanted with anabolic agents and bulls of Friesian and Charolais x Friesian breeds of cattle. Percent and mean cross-sectional areas (CSA) of three myofiber types (βR, {alpha}R and {alpha}W) were determined. The percentage of βR myofibers did not vary significantly with treatment. The implanted steers had 26% more {alpha}R and 8% less {alpha}W myofibers than the untreated steers, while the bulls had 33% more {alpha}R and 20% less {alpha}W 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 {alpha}R 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 {alpha}W 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, {alpha}R and {alpha}W myofibers, and in the sizes of the βR and {alpha}R myofibers. No evidence of myofiber abnormality was found in any of the samples examined.

Footnotes

1 Present address: Faculty of Vet. Med., University College Dublin, Ballsbridge, Dublin 4.






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Copyright © 1986 by the American Society of Animal Science.