Factorial experiment reveals stable overall leg health across probiotic and antibiotic diets in broilers, indicating welfare impacts vary by biological domain.
Key Points
To establish an individual-level multidimensional welfare framework evaluating broiler leg health across five biological domains under probiotic supplementation, antimicrobial growth promoters, and environmental enrichment.
Conducted a 3 × 2 factorial experiment evaluating 1,440 male broilers across 48 pens assigned to negative control, zinc bacitracin, or multi-strain probiotic diets, with or without environmental enrichment.
Assessed leg health across five domains: locomotor performance, skeletal mineralization, postural deformity, cartilage and joint disorders, and spinal and muscular disorders, normalizing indicators onto a 0–1 scale.
Analyzed domain scores and a global welfare-response index using mixed-effects models with dietary additive, enrichment, and their interaction as fixed effects and pen as a random effect.
The global welfare-response index ranged from 0.727 ± 0.022 in the control with enrichment group to 0.759 ± 0.013 in the control without enrichment group, with no significant effects of dietary additive (P = 0.599), enrichment (P = 0.207), or their interaction (P = 0.715).
Probiotic supplementation with enrichment yielded the highest skeletal-mineralization score (0.631 ± 0.026), but differences were not significant for dietary additive (P = 0.150), enrichment (P = 0.933), or their interaction (P = 0.758).
Dietary additive and enrichment showed a statistical trend toward an interaction for postural deformity (P = 0.073), whereas locomotor, cartilage and joint, and spinal and muscular domains showed no significant effects (P > 0.05).