Nest building before farrowing is one of the most strongly motivated behaviors in sows. Denying this behavior causes significant welfare harm during a critical reproductive period.
Nest building is among the strongest behavioral motivations documented in farm animals. Research using preference testing shows sows will work intensively to access nesting material before farrowing, and deprivation causes measurable physiological stress and behavioral frustration. The frustration of this motivation during the pre-farrowing period - an already stressful time physiologically - compounds welfare harm at a vulnerable moment. The welfare case for providing nesting material is clear and the practical barrier is minimal in systems that already provide bedded housing. Even in farrowing crates, providing manipulable material that allows some nesting expression significantly reduces welfare harm compared to no provision at all.