Serological examination
Serum samples were collected at dpv 0, 7, 14, 21, and 28 and dpi 3, 5,
7, 10, 14, and 21. PRRSV-specific antibodies were measured using a
commercial ELISA kit (IDEXX, Inc., Westbrook, ME, USA) according to the
manufacturer’s instructions. The PRRSV-specific antibody titre was
reported as the S/P ratio, and the serum samples were considered
positive if the S/P ratio was ≥0.4.