Effect on total pigs weaned of herd closure for elimination of porcine reproductive and respiratory syndrome virus

Herd closure has been reported as a method to eliminate porcine reproductive and respiratory syndrome virus (PRRSV) from breeding herds. However, there is concern that while closing the herd to animal entries may aid in elimination of PRRSV, productivity of the herd may decrease, at least temporarily. Herd closure was conducted at 15 multiplication herds as part of a PRRSV eradication program beginning in December 2001. All herds tested positive for porcine reproductive and respiratory syndrome (PRRS) by ELISA prior to closure, and three were known to be infected. All herds were preloaded with gilts and closed for an average of 260 days. After closure, all farms tested negative for PRRSV by polymerase chain reaction and have remained negative for 4 years. The impact of closure was evaluated by comparing the number of pigs weaned during the 52 weeks prior to the day of closure to that achieved for the 52 subsequent weeks. Of the 15 herds, 13 had produced at least the same total number of weaned pigs at 52 weeks after closure. Number of services per week and change in farrowing rate accounted for 60% of the variability observed in total pigs weaned per week.