Outdoor access for pigs - through free-range or outdoor systems - allows expression of fundamental rooting and foraging behaviours that cannot be met in indoor environments.
Outdoor access represents a qualitative welfare improvement for pigs beyond what any indoor enrichment can provide. The opportunity to root in soil, explore a varying environment, experience weather and express a full range of natural behaviours benefits both physical and psychological welfare. The limitations of indoor enrichment - however good - cannot fully substitute for access to an outdoor environment.