Antibody titers to pseudorabies virus in piglets immunized with gIII deleted pseudorabies vaccine in a pseudorabies infected herd. 
The decrease in titer of PRV antibodies in serum was evaluated at 10, 37, 67, 109 and 173 days of age in 16 non-vaccinated pigs and 43 pigs vaccinated at 3, 67 and 80 days of age with a modified live TK/gIII gene deleted pseudorabies virus (PRV) vaccine.  Serum samples were analyzed for antibodies to PRV by the serum-virus neutralization test (SN), a commercial competitive ELISA (CELISA), and the CELISA OMNIMARK PRV differential (OMD) diagnostic kit.  At 10 days of age, all pigs had SN titers > or = 1:4 and were CELISA+/OMD+, indicating circulating antibodies to field strains of PRV.  At 109 days, all non-vaccinated pigs had SN titers < 1:4.  Forty-five percent of vaccinated pigs had SN titers > or = 1:4, 56% were CELISA positive and most were CELISA+/OMD-, indicating antibodies due to vaccination.  At 24 weeks of age, all pigs had SN titers > or = 1:4 and were CELISA+/OMD+ due to exposure to field strains.  Although circulating maternal antibodies interfere with the development of active immunity, vaccination at 3 days of age resulted in detectable antibodies by 67 days of age, and a limited immune response could be measured at 109 days of age.