ABSTRACT

Background and Aim: Lameness is a major welfare and economic concern in fast-growing broiler chickens, particularly under tropical intensive production systems where environmental stressors are pronounced. Despite its multifactorial etiology, large-scale field evidence quantifying the combined effects of housing microclimate on lameness in Southeast Asian closed-house systems remains limited. This study aimed to identify age-specific environmental predictors of lameness in commercial Cobb 500 broilers raised under tropical closed-house conditions. 

Materials and Methods: An observational study was conducted using data from 296 broiler flocks (11.45 million birds) across five commercial farms in Eastern Thailand during 2023. Lameness incidence was derived from culling records. Environmental parameters included temperature, relative humidity, temperature–humidity index (THI), light intensity, and ammonia concentration. Statistical analyses comprised descriptive statistics, General Linear Model, Pearson’s correlation, and multivariable regression, with assessment of multicollinearity. 

Results: The median lameness incidence was 1.00% (interquartile range: 0.76–1.38%), with significant variation among farms (p < 0.0001). Early-life thermal conditions were strongly associated with lameness, with day 1 maximum temperature showing a positive correlation (r = 0.54, p < 0.0001). Diurnal temperature variation on day 7 exhibited a negative association (r = −0.36, p < 0.0001), indicating the importance of thermal stability. Light intensity demonstrated the strongest association during mid-growth, particularly on day 14 (r = 0.56, p < 0.0001). Ammonia concentration became a significant factor during late production stages (day 28 onward; r = 0.31–0.41, p < 0.0001). THI values consistently exceeded recommended thresholds, indicating sustained thermal stress. The final multivariable model explained 42.9% of the variation in lameness incidence (adjusted R² = 0.416), identifying day 7 diurnal temperature variation and day 14 light intensity as independent predictors. 

Conclusion: Lameness in tropical broiler systems is strongly influenced by age-specific environmental conditions. Early thermal stress and excessive mid-growth light intensity emerged as critical predictors, while late-stage ammonia accumulation further increased risk. These findings highlight the importance of precise microclimate management, particularly during early and mid-growth phases, to improve broiler welfare and reduce economic losses in tropical closed-house production systems. 

Keywords: ammonia concentration, broiler chickens, environmental management, lameness, light intensity, temperature fluctuation, Thailand, welfare.