The drive to build a nest before giving birth is one of the strongest motivational states in sows, and its prevention in conventional farrowing crates causes acute and measurable suffering.
Pre-farrowing nesting motivation is one of the most robustly documented welfare deprivations in farm animal science. The sow that paws frantically at a bare metal floor for hours before giving birth is not behaving oddly — she is performing a behaviour that evolution has made her highly motivated to complete, in an environment that makes completion impossible. The frustration is acute, measurable and directly affects the welfare of the piglets born afterward. Providing even minimal substrate — straw, jute — in farrowing crates substantially reduces this welfare cost. Freedom farrowing systems that allow full nest construction represent the gold standard. Both are feasible; the barrier is economic inertia, not technical impossibility.