The Effects of Androgen on Histochemical Fiber Composition of M. Semispinalis Cervicis in the Cock

Abstract

The effects of androgen on the fiber composition of M. semispinalis cervicis in the cock were histochemically investigated. Six intact cocks, six capons and six testosterone propionate treated capons were sacrificed at 30 weeks of age. Based on the histochemical reactions of myosin adenosinetriphosphatase and NADH-tetrazolium reductase, the fibers of M. semispinalis cervicis were divided into three types, namely types I-R, II-R and II-W. M. semispinalis cervicis, which is a red muscle, has type I-R fibers as the thickest of all fiber types. There was no significant difference in the proportional distribution of the fiber types among the experimental groups. But the diameters of all the three fiber types were significantly smaller in capons than in intact cocks. The difference in the thickness of muscle fibers between intact cocks and capons was more apparent in type II (fast-twitch) fibers than in type I (slow-twitch) fibers. This result suggests that type II fibers have a higher sensitivity to androgen, on which their development in size relies to a great extent, and would work when the muscle is called upon to perform temporary and powerful tasks such as sexual behavior or fighting.