Herd closure is one possible method to eliminate porcine reproductive and respiratory syndrome virus from entering breeding herds. While preventing animal introductions may help eliminate PRRS exposure, a significant concern revolves around the prospect of decreased productivity.
Prior to closure, ELISA tests found all herds tested positive for PRRS, and three were known to be infected.
All herds were preloaded with gilts and closed for an average of 260 days.
Following closure, all farms tested negative for PRRS by polymerase chain reaction and remained negative for four years.
Researchers evaluated the impact of closing a herd by looking at the number of pigs weaned during the 52 weeks prior to the day it was closed and comparing that with 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. Researchers note that the number of breeding services per week and farrowing rate changes accounted for 60 percent of the variability in total pigs weaned per week.