Outdoor access for pigs allows expression of rooting and foraging behaviors that are strongly motivated and central to pig psychological welfare.
Rooting in soil represents a behavioral need for pigs that extends beyond simple food-finding. The physical engagement of pushing the snout through yielding substrate, the rich olfactory stimulation of soil microbiology, and the unpredictable discovery of food items engages multiple sensory systems that evolved for this activity. Pigs denied rooting opportunity on hard substrates direct this behavior toward pen fittings and pen-mates, causing mutual harm. Outdoor access that provides actual soil rooting opportunities addresses this need most completely. For indoor systems, provision of deep litter or rooting substrates is the best available alternative.