Horses were inoculated with several strains of virulent PRRS virus. Sera from the horses were tested for the presence of PRRS virus-neutralizing antibodies.

Large volumes of equine plasma were collected and used to passively immunize piglets. Sera were collected at various time points after immunization and tested for virus-neutralizing activity.

These results show that horses are capable of generating high neutralizing antibody titers to PRRSV when exposed to virulent virus. Piglets develop neutralizing antibody titers to PRRSV when passively immunized with a sufficient volume of ά-PRRSV equine plasma.