Comparative growth performance in different Japanese quail lines: the effect of muscle DNA content and fiber morphology.

The aim of this study was to investigate the DNA content and morphological characteristics of muscle fibers, and their relation to the growth performance in random bred control (RBC) and heavy weight (HW) Japanese quail lines. The 2 lines were of similar embryo size at 6 and 8 d of incubation; however, HW quail were significantly larger than their counterparts after 10 d of incubation (P < 0.05). The hatch weight of the HW quail line was approximately 1.3-fold higher than the RBC quail line (P < 0.001). After 15 d posthatch, the BW and pectoralis major muscle weight (PMW) exhibited remarkable differences between the 2 quail lines. The RBC line showed a faster rate of increase in PMW (2.7- vs. 2.1-fold) and total DNA mass (2.2- vs. 1.6-fold) between 0 and 4 d posthatch. The HW line exhibited a greater rate of the PMW (33.0- vs. 12.9-fold) and total DNA mass (10.3- vs. 4.0-fold) between 4 and 15 d posthatch than the RBC line. Moreover, the greatest increase in total DNA mass occurred between 0 and 8 d posthatch for the RBC line and 4 to 15 d posthatch for the HW line. These differences in the DNA content indicate a difference in the hypertrophic potential of muscle fibers between the 2 quail lines. The cross-sectional area of muscle fibers was 1.3-fold greater in the HW line compared with the RBC line at 8 d posthatch (158.5 vs. 97.11 μm(2), P < 0.001), and this difference increased with age (over 2.1-fold greater in the HW line). Thus, the most important time windows affecting ultimate body and muscle weights in the RBC and HW quail lines are between 0 to 8 d and 4 to 15 d posthatch, respectively. Rapid muscle growth rate and a greater muscle mass in the HW quail line may be partially due to the hypertrophic potential of muscle fibers, which is characterized by larger fiber size.