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In order to investigate the influence of stocking density on broiler welfare, 17,616 Ross chickens were assigned to three different treatments: T1, T2 and T3 with a final stocking density of 27, 35 and 43 kg/m2, respectively (corresponding to an initial density of 12, 16 and 20 birds/m2). Animal welfare was assessed by measuring behavioural, physiological and productivity traits. Behavioural observations included the disturbance frequency of resting birds by other birds, the duration of the lying bouts and the standing/lying ratio. The heterophil/lymphocyte ratios were assessed from blood collected before departure to the slaughterhouse. Main productivity traits were the final live weight and carcass degradation due to foot and pad dermatitis and breast blisters. Most of the observed parameters were adversely affected by the highest density (P < 0.05). Between T1 and T2, some traits tended to demonstrate that a better degree of bird welfare existed in T1 (higher standing/lying postures ratio and final live weight, lower frequency of pododermatitis and hock lesions; P < 0.05) whereas other traits showed no differences (frequency of disturbances by other birds during resting, heterophil/lymphocyte ratio). In conclusion, a stocking density of 43 kg/m2 seemed to induce poor bird welfare whereas it was not clearly demonstrated that 27 kg/m2 was better than 35 kg/m2.