Four groups of boars each comprising 5 boars of 1 to 1.5 years of age were
designated as group 1-4, respectively. The boars in group 1, 2 and 3 were obtained from
PRRSV-antibody-negative herds, and were subsequently confirmed to be seronegative
for PRRSV antibodies by indirect enzyme-linked-immunosorbent assay (ELISA) and
immunoperoxidase monolayer assay (IPMA). Group 1 served as a non-vaccinated
control group and group 2 and 3 were vaccinated with two different PRRS-vaccines.
Group 4 consisted of previously PRRSV infected, PRRSV antibody positive boars
obtained from Danish AI-centres. All 5 boars were confnmed to be seropositive for
PRRSV antibodies by ELISA immediately before challenge.