The way that sows are housed during gestation and lactation has moved towards more intensive systems so that sows can be more easily managed and production maximized. At a minimum, some of these factors have contributed to a decline in the productive life of sows in commercial pork production systems. A sow remaining in the breeding herd for fewer parities is likely to produce fewer pigs in her lifetime, compared to a sow that remains in the breeding herd for a longer period of time. This reduces the opportunity of a sow to be sufficiently productive (pigs weaned and sold per lifetime) to achieve a return on the replacement gilt investment cost.