Nesting Behavior in Sows: A Thwarted Reproductive Drive

Pre-farrowing nesting behavior is among the most strongly motivated behavioral needs of sows, and its prevention in conventional farrowing crates represents a severe and well-documented welfare compromise.

Key Facts

Wild and feral sows spend 5-7 hours gathering vegetation and constructing a nest in the 24 hours before farrowing — a behavior driven by intense hormonal motivation.
The nesting drive peaks in the hours immediately before birth and is associated with surges in prolactin and other reproductive hormones.
Sows in conventional farrowing crates, which prevent all movement, show redirected nesting behaviors (rooting at the floor, champing) for hours before farrowing — indicating strong, unresolved motivation.
Research using preference testing shows sows will work hard (push weighted doors, withstand aversive stimuli) to access nesting material before farrowing.
Sows given nesting material in systems that allow nesting show reduced cortisol levels, less restlessness, and shorter active farrowing duration compared to sows without material.
Some alternative farrowing systems (free farrowing pens) provide rooting substrate allowing partial nesting expression while maintaining piglet protection through design rather than physical restraint.
Sweden banned farrowing crates in 1988; other countries including Switzerland and Norway have followed, while the EU is working toward broader restrictions.

Welfare Considerations

The prevention of nesting behavior in conventional farrowing systems is one of the clearest examples of a thwarted behavioral need in commercial livestock production. Unlike some motivated behaviors where the welfare impact of deprivation is uncertain, the evidence that nesting deprivation causes acute frustration and stress in pre-farrowing sows is robust and replicated across multiple studies using diverse welfare indicators. Sows confined in farrowing crates during the pre-farrowing period display persistent redirected behaviors, elevated stress hormones, and behavioral indicators of frustration for hours before birth. The hormonal cascade driving nesting is ancient and deeply embedded in reproductive physiology — it cannot simply be suppressed by confinement, only frustrated. This represents a preventable source of suffering at a scale affecting millions of sows globally each year.

What You Can Do

Support free farrowing legislation that enables sows to express nesting behavior while protecting piglet welfare.
Choose pork products from farms certified to allow sow nesting and free farrowing where available.
Advocate for EU-wide and global bans on conventional farrowing crates that prevent all movement.
Support research into free farrowing system designs that balance sow welfare with piglet survival outcomes.
Learn about the scientific evidence on sow nesting motivation and share it with others interested in farm animal welfare.