Nesting behaviour in sows is among the most strongly motivated behaviours in any farm animal. Frustrating it in confinement systems causes measurable distress; providing nesting material is a high-impact welfare intervention.
Nesting behaviour in sows is one of the clearest examples of a thwarted highly motivated behaviour in modern pig production. The instinct to build a nest before farrowing is ancient, deeply embedded, and physiologically linked to the hormonal cascade of parturition. When sows cannot perform this behaviour in barren confinement systems, they show stereotypic rooting and pawing, increased vocalisation, and agitation that represents genuine psychological suffering. Providing even a handful of straw allows partial expression of nesting behaviour and measurably reduces this distress. Full nest-building opportunity in deep-bedded freedom farrowing systems represents the gold standard. That a partial solution (straw provision) is so effective, cheap, and easy to implement makes its absence in systems that lack it particularly difficult to justify.