Farrowing crates confine sows around the time of birth to prevent piglet crushing, but restrict their freedom of movement during the most physically demanding period of their lives.
Farrowing crates prevent sows from performing nesting behavior - rooting, gathering material, and building a nest - that is strongly motivated before farrowing. The inability to perform this instinctive behavior causes visible frustration. Confinement during farrowing itself prevents position changes that may help during labor. The 4-6 week confinement covers the most physically demanding phase of the reproductive cycle when adequate movement is most important for welfare. Free-farrowing alternatives exist that maintain comparable piglet survival while allowing sow movement, demonstrating that the welfare compromise of crates is manageable rather than necessary.