Differential developmental characteristics of myofibers in the leg muscles of fast- and slow-growing Bian chicken lines

In this study, we aimed to compare muscle fibre characteristics between fast- and slow-growing Bian chicken lines at three key developmental stages: late embryonic stage, early postnatal stage, and market ages. The weights of 30 fast- and slow-growing roosters were compared at birth and at the 16 weeks. At embryonic ages of 14, 17 and 19 days (E14, E17 and E19), as well as at the ages of 1 and 16 weeks, three roosters from each group were slaughtered. Their leg muscles were analysed to compare muscle fibre morphology, the abundance of fast- and slow-twitch muscles, and gene expression. The results showed that the birth weight and 16 weeks body weight were significantly higher in the fast-growing Bian chicken line than in the slow-growing line. Muscle fibre density was higher in the fast-growing Bian chicken line than in the slow-growing Bian chicken line at E19 and at 1 week. Moreover, muscle fibre diameter, cross-sectional area, and fast-twitch muscle content were higher in the fast-growing Bian chicken line at 16 weeks. The expression levels of the slow skeletal muscle marker gene <i>TNNI1</i> in the leg muscles of both lines were significantly upregulated during the late embryonic stage (E14–E19) compared to those detected at the postnatal periods (1 and 16 weeks). However, the slow-growing line exhibited more pronounced embryonic protein accumulation. In summary, these results indicate that the selection of fast-growing lines can effectively improve the overall growth performance of Bian chickens and increase muscle yield. The fast-growing Bian chicken line has a clear growth advantage over the slow-growing Bian chicken line.During the late embryonic stage and early postnatal period, the fast-growing Bian chicken line exhibited higher myofiber density than the slow-growing Bian chicken line.The fast-growing Bian chickens exhibit a high proportion of fast-twitch fibres and muscle mass through muscle fibre type conversion post-hatching. The fast-growing Bian chicken line has a clear growth advantage over the slow-growing Bian chicken line. During the late embryonic stage and early postnatal period, the fast-growing Bian chicken line exhibited higher myofiber density than the slow-growing Bian chicken line. The fast-growing Bian chickens exhibit a high proportion of fast-twitch fibres and muscle mass through muscle fibre type conversion post-hatching.