Growth performance and muscle histological characteristics of IPB-D3 chickens reared under intensive and free-range systems.

BACKGROUND AND AIM: IPB-D3 chicken is a locally developed fast-growing composite line derived from Pelung, Sentul, Kampung, and Broiler strains. Despite its potential as a dual-purpose Indonesian breed, detailed information on its muscle histology, especially type IIX myofiber composition under different rearing systems, is lacking. This study aimed to evaluate the growth performance and muscle histological characteristics of IPB-D3 chickens reared under intensive and free-range systems. MATERIALS AND METHODS: Ninety 12-week-old IPB-D3 chickens were reared for 12 weeks under two systems: intensive (n = 45) and free-range (n = 45). Samples of pectoralis major and quadratus femoris (Fem) muscles from 10 birds (five per group) were examined using hematoxylin-eosin, picrosirius red, and immunohistochemical staining for type IIX myofibers. Parameters such as fasciculus area, myofiber cross-sectional area, myofiber number per mm(2), collagen percentage, and type IIX fiber intensity were analyzed using an independent t-test at a 95% confidence level (Statistical Package for the Social Sciences v.29.0). RESULTS: No significant difference (p > 0.05) was observed in body weight or carcass yield between rearing systems. However, free-range chickens exhibited a significantly larger myofiber cross-sectional area and a higher proportion of high-intensity type IIX myofibers in the Fem muscle (p < 0.05), while the intensive system showed a higher percentage of intramuscular collagen (p < 0.05). The overall muscle morphology was similar between systems, with polygonal myofibers organized within collagen-bound fasciculi. CONCLUSION: This study provides the first histological characterization of IPB-D3 chickens, demonstrating that both rearing systems support comparable growth performance. Free-range rearing enhances thigh muscle hypertrophy and type IIX fiber development, whereas intensive rearing increases collagen deposition. These findings suggest that IPB-D3 chickens are adaptable to diverse production environments. Further studies should explore Myosin heavy chain gene expression, longitudinal muscle growth, and meat texture properties to improve sustainable rearing strategies and meat quality optimization for Indonesian local chicken development.