Increased Space Allowance Improves Productivity and Welfare in Growing Pigs Assessed Using Artificial Intelligence-Based Monitoring of Agonistic Behavior

Rearing density influences pig productivity and welfare, but its behavioral and physio-logical effects remain unclear. This study evaluated how increasing space allowance from 0.57 to 0.97 m²/pig affects growth, agonistic behavior, and stress in growing pigs. Seventy-six 12-week-old pigs were allocated to high or low rearing density (HRD: 12 pigs/pen, <i>n</i> = 4 pens; LRD: 7 pigs/pen, <i>n</i> = 4 pens) for 28 days by varying pig numbers within identical pens. Growth performance was recorded weekly, while agonistic behavior was continuously monitored using RGB cameras and detected with a YOLOv8-based model (overall mAP50 = 0.953; aggression = 0.960, ear biting = 0.927, tail biting = 0.972). Ear base temperature was measured at baseline and twice weekly, lesion scores were assessed at trial completion, and blood biochemical parameters were also assessed. Pigs under LRD exhibited higher (<i>p</i> < 0.01) body weight, daily gain, and feed intake, with a lower feed conversion ratio than HRD pigs. Increased space allowance reduced (<i>p</i> < 0.05) agonistic behavior, lesion scores, plasma glucose, free fatty acids, cortisol, and ear base temperature. These findings indicate that increased space allowance improves growth and welfare and demonstrate the value of AI-based behavioral monitoring in pig production systems.