THE INTRODUCTION OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS ( PRRSV ) SERONEGATIVE REPLACEMENTS INTO PRRSV-SEROPOSITIVE HERDS

Dachrit Nilubol Brad Thacker THE INTRODUCTION OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV) SERONEGATIVE REPLACEMENTS INTO PRRSV-SEROPOSITIVE HERDS The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) status of a herd dictates how PRRSV-negative replacements are introduced into a herd. In a herd free of PRRSV, the PRRSV-negative replacement can be readily introduced after a 21-day isolation period followed by 21-days of acclimatization, which is to ensure the PRRSV status of the replacement pigs and to expose them to other organisms that might exist in the herd. In a seropositive herd with or without PRRSV circulating, the PRRSV-negative replacement cannot be readily introduced. The PRRSVnegative replacement must be acclimatized by exposing them to the herd-specific strains of PRRSV in order to develop immunity. The introduction of PRRSV-negative pigs without acclimatization may lead to an outbreak of PRRS due to transmission from chronically infected sows. Prior to their introduction into the breeding herd, they should have recovered from the infection and ceased virus shedding. If a herd, positive for PRRSV, has the virus circulating, it is suggested restocking ceases for 4-6 months, to achieve endemic levels of PRRSV (herd stabilization). Once the herd starts weaning negative piglets, then restocking can resume. In a seropositive herd with no virus circulating, it is not recommended to readily introduce PRRSV-negative replacements. The herd must be evaluated for virus transmission by using sentinel pigs. If sentinel pigs remain negative, the negative replacement can be introduced. In contrast, if the sentinel pigs seroconvert, those pigs should be removed and the process started over again.