Decay of Colostrum-Derived Antibodies to Porcine Reproductive and Respiratory Syndrome (PRRS) Virus in Neonatal Swine Nursing Immune Dams

and Implications The decay of colostrum-derived antibodies specific for porcine reproductive and respiratory syndrome virus (PRRSV) was characterized in young pigs. Six pigs per litter were randomly selected from seven multiparous sows in a commercial sow herd. Prior to farrowing, all sows were confirmed seropositive to PRRSV. Colostrum and serum samples were collected from each sow at the time of farrowing. The pigs were weaned and transported to an isolated facility at 7-10 days of age. Sera were collected periodically from all pigs between 3 and 40 days of age and assayed for PRRSV-specific antibodies by the serum neutralization (SN) test and ELISA. Serum and colostrum samples also were assayed for the presence of PRRSV. No virus was isolated from any of the serum or colostrum samples. During the observation period 10 of 42 pigs (ELISA) and 17 of 42 pigs (SN) showed a normal decay of antibodies. The mean half-life for the decay of maternal antibodies was estimated to be 16.2 days (ELISA) and 8.14 days (SN) (i.e., a relatively short half-life). A number of pigs, however, seroconverted during the observation period. Becasue there was no apparent source of virus, this suggested that colostrum or milk could be a source of virus. Early weaning (7-10 days) appeared to be ineffective at eliminating PRRSV infections in pigs.