Locomotor Health in Modern Broiler Chickens: Risk Factors, Major Disorders, Assessment Methods, and Implications for Welfare and Production Efficiency.

Genetic selection for rapid growth, improved feed efficiency, and increased breast-muscle yield has substantially enhanced broiler production; however, it has also increased the functional demands placed on the locomotor system. This review critically examines locomotor health in modern broiler chickens in relation to welfare and production efficiency. Particular attention is given to the multifactorial interactions among genotype, growth rate, body weight and conformation, skeletal development, nutrition, physical activity, housing conditions, age, and infectious factors. Major locomotor disorders, including valgus-varus deformities, tibial dyschondroplasia, infectious arthritis and tenosynovitis, bacterial chondronecrosis with osteomyelitis, osteochondrosis, rickets, and fractures, are discussed in terms of their biological basis and welfare consequences. The review also evaluates current approaches to locomotor assessment, including gait scoring, standing ability, latency-to-lie testing, radiography, post-mortem examination, biomarkers, infrared thermography, force-plate analysis, and camera- and sensor-based monitoring. Evidence indicates that locomotor disorders should not be attributed solely to rapid growth but rather to insufficient coordination between increasing body mass and the adaptive capacity of skeletal and muscular tissues. Future strategies should integrate balanced genetic selection, precision nutrition, activity-promoting environments, and precision livestock farming technologies for early detection of impaired mobility. Such an integrated approach may help maintain high production efficiency while improving broiler welfare, supporting locomotor health, and reducing production losses.