Influence of age and maternal antibodies on antibody responses of neonatal piglets vaccinated against Mycoplasma hyopneumoniae

Objective: To assess the relative importance of age and maternal antibodies on antibody responses of neonatal piglets to a commercial Mycoplasma hyopneumoniae vaccine. Methods: Piglets from 20 sows in each of two commercial swine operations (with serological evidence of M hyopneumoniae exposure) were vaccinated once at 2, 3, or 4 weeks of age with an M hyopneumoniae bacterin, or were nonvaccinated controls. Serum IgG antibodies were assayed by ELISA, using surface antigens of M hyopneumoniae, in serum samples collected from pigs in the first week of life and at prevaccination, 3 weeks postvaccination, and 2.5 months of age. Sows were vaccinated against M hyopneumoniae in Herd B, but not in Herd A. Results: In Herd A, piglets had moderate titers of maternal antibodies. Vaccinated pigs had significantly higher antibody responses than nonvaccinates. Higher prevaccination titers were associated with lower responses. Age at vaccination was not associated with response to vaccination. In Herd B, piglets had high titers of maternal antibodies. Antibody titers of vaccinated pigs did not decline as rapidly as those of nonvaccinated pigs, and vaccinates had higher titers at 2.5 months of age. Implications: Titer of maternal antibodies, but not age (ie, immaturity of immune function), is a major concern when piglets are vaccinated against M hyopneumoniae. Vaccination of pigs as young as 2 weeks of age may induce active antibody responses in the presence of moderate titers of maternal antibodies. Caution should be used in extrapolating these findings to other vaccines and vaccination protocols