Segregated early weaning has also been used to produce PRRSV-negative pigs from infected sows. However, depending on the level of PRRSV activity in the sow herd, production of PRRSV-negative batches may not be consistent (Donadeu et al. 1999; Gramer et al. 1999). All-in/all-out segregated production of batches of weaned pigs is needed to maximize the success of this technique. In addition, the establishment of PRRSV-negative herds from positive sources is possible when negative piglets are produced by the combination of several of these techniques (Torremorell et al. 2002).