Announcing the arrival of enrichment increases play behaviour and reduces weaning-stress-induced behaviours of piglets directly after weaning

Piglets have difficulties with the abrupt changes at weaning associated with conventional pig production systems. Previously, it has been shown in rats that reward and announcement of reward counteracts impact of stress effects. In the present study, it was investigated if announcement of an environmental enrichment, more than enrichment alone, could facilitate play behaviour and reduce weaning-stress-induced behaviours such as increased aggression with subsequent increased injuries and increased social manipulative behaviours (i.e., tail biting, belly nosing, mounting). Twenty-four litters of conventional housed fattening piglets were kept under three different experimental conditions: sound cue (conditioned stimulus, CS) paired with an environmental enrichment (unconditioned stimulus, US) with a maximum delay between the CS and US of 30 s (CS–US paired) in which anticipatory behaviour develops; cue-environmental enrichment unpaired (CS–US unpaired) and no cue and no environmental enrichment (No CS–US). At two weeks of age the so-called ‘anticipation procedure’ started and ended two days after weaning. Growth, play, aggressive, social manipulative, eating and inactive behaviour, and injury rates were measured before and after weaning. Results of this study indicated that announcement of enrichment and not enrichment alone significantly increased play behaviour after weaning. In addition, announcement of enrichment and to a lesser extent enrichment alone decreased aggression before and after weaning and subsequent amount of injuries after weaning. The most important finding of this study is that the effects of an expected enrichment are more pronounced than the effects of enrichment alone. It is therefore suggested that announcing enrichment has an additional effect on the impact of enrichment alone and can be used as a new tool to reduce weaning stress in piglets.