Sow immunity plays an important role in preventing viral infection and disease in newborn piglets. Vertical transmission of porcine circovirus type 2 (PCV2) may perpetuate porcine circovirus associated disease (PCVAD) in newborn and growing pigs. Hence, the immunological effects of maternal immunoglobulin transfer of PCV2-specific antibodies on PCV2 viremia and immune response in piglets in commercial swine herds were evaluated. Sow vaccination has been shown to reduce viral shedding and viremia, and increases the neutralizing antibody (NA) titers. Since NAs are important for control of PCVAD and mammary secretions may contain high anti-PCV2 NA levels, we examined the PCV2 NA levels in colostrum, milk, sow serum, and piglet serum over time to investigate an association between NA levels and protection against infection. NA titers were remarkably high (up to 10-6 50% neutralizing titer) in sow serum and colostrum on all farms regardless of viremia levels. In piglets vaccinated at 3 weeks of age, NA titers peaked at 10 weeks of age and continued to maintain high viral neutralizing titers to slaughter. The impact of maternally derived neutralizing activity was most evident during the suckling period. Although PCV2 was transmitted from sows to piglets in colostrum, piglets were largely nonviremic at weaning. Thus, NAs appear to control or suppress initial infection even though they are unable to clear or prevent infection later in life.
Keywords: PCV2; mammary secretions; maternal immunity; neonatal immunity; neutralizing antibodies.