Simulated loading and unloading of pigs of two slaughter weights: effects of the group size on their ease of handling and physiological response

This study aimed to evaluate the effects of handling barrows of two slaughter weights, light (L: 135.1 kg average final weight) and heavy (H: 152.9 kg average final weight), and group sizes (3 vs. 6 pigs/group) through a simulated loading and unloading procedure on their behavioural and physiological response. Behaviour was observed in 120 pigs, while heart rate (HR) and whole blood lactate concentrations were evaluated in a subsample of 81 pigs (3 pigs/group). The interaction body weight × group size had no effect on handler interventions, pig behaviours, and post-handling blood lactate concentration. Handling time was longer in H pigs (P = 0.05), but the number of handler interventions and paddle noise was greater only in larger groups of pigs (P ≤ 0.05), resulting from their higher frequency of turning back, backing-up, and going backward (P = 0.04, P = 0.02, and P = 0.04, respectively). Pigs handled in larger groups presented greater post-handling blood lactate concentrations (P < 0.01). In L pigs, the HR increased more when handled in smaller than larger groups (P = 0.03) without significant consequences during the recovery period. Our results suggest that a smaller group size would reduce pigs’ fatigue and ease their handling.