Behavioural differences between weaner pigs with intact and docked tails

Tail-biting in pigs (Sus scrofa) reduces welfare and production. Tail-docking reduces (but does not eliminate) tail-biting damage. The reason tail-docking reduces tail damage is unknown. It may reduce pigs’ attraction to tails (H1), or increase tails’ sensitivity to investigation (H2). To investigate these hypotheses, behavioural differences between 472 individually marked grower pigs with intact tails (nine groups of 25–34 pigs) or docked tails (nine groups of 22–24 pigs) were observed from 5–8 weeks of age on a commercial farm in Denmark. Pens had part-slatted floors, dry feeding and two handfuls of straw per day, and enrichment objects were provided. Behavioural sampling recorded actor and recipient for tail-directed (tail interest, tail in mouth, tail reaction) and investigatory behaviours (belly-nosing, ear-chewing, interaction with enrichment). Scan sampling recorded pig posture/activity and tail posture. Intact-tail pigs performed more overall investigatory behaviours but tail type did not affect the amount of tail-directed behaviours. Larger pigs performed more investigatory and tail-directed behaviours than smaller pigs and females performed slightly more tail investigation. Tail-directed behaviours were not consistent over time at the individual or group level. However, ear-chewing was consistent at the group level. One group with intact tails was affected by a tail-biting outbreak in the final week of the study (evidenced by tail-damage scores) and showed an increase over time in tail posture (tail down) and tail-directed behaviour but not activity. Overall, there were few behavioural differences between docked and undocked pigs: no evidence of reduced tail investigation (H1) or an increased reaction to tail investigation (H2) in docked pigs, and yet docked pigs had less tail damage. We propose that docking might be effective because longer tails are more easily damaged as pigs are able to bite them with their cheek teeth.