Nesting behaviour in sows before farrowing is a strong motivation that, when frustrated by farrowing crate confinement, causes significant welfare-relevant stress in late-gestation sows.
Nesting frustration in confined sows is a welfare problem of significant magnitude - a highly motivated behaviour completely prevented at one of the most physiologically stressful times in the reproductive cycle. Providing any nesting material, and ideally loose housing that allows genuine nest building, represents a meaningful welfare improvement.