An analysis of skeletal muscle response to selection for rapid growth in Japanese quail (Coturnix coturnix Japonica).

A line of Japanese quail selected for high body weight at 4 weeks of age (P line) was compared to an unselected control (C) line at 10, 23 and 56 days of age. The increase in the weight of the pectoralis major and supracoracoideus muscles in the P line was paralleled by an increase in total DNA, RNA and protein content of the muscles when compared to comparable age C line. DNA, RNA and protein concentrations and RNA/DNA and protein/DNA ratios were similar between lines within age. Greater muscle mass in the P line was accomplished primarily through an increase in the total number of muscle nuclei rather than through an increase in DNA unit size. Ca2+-activated myosin ATPase, total phosphorylase and succinic dehydrogenase enzyme activities were similar between lines and across ages in the pectoralis major and supracoracoideus muscles. The semimembranosus muscle possessed 59% more alpha fibers and only 7% more beta fibers in the P line when compared to the C line. Semimembranosus alpha fiber diameters were not significantly different between lines within age, while beta fiber diameters were significantly greater in the P line. Estimated beta fiber contribution to total semimembranosus muscle cross sectional area revealed no significant difference between lines within age. There was a significant increase in the length of the femur and humerus in the P line when compared to C line within age, indicating that some of the increased muscle weight of the P line quail was due to an increase in muscle length in addition to an increase in muscle cross-sectional area.