CLINICAL PROTECTION, VIREMIA AND IMMUNE RESPONSE IN PIGS VACCINATED AGAINST PCV2 AT DIFFERENT AGES WITH DIFFERENT LEVELS OF MATERNAL IMMUNITY AS DERIVED FROM VACCINATED GILTS AND SOWS UNDER FIELD CONDITIONS

The study aims at evaluating the clinical protection, the level of PCV2 viremia and the immune response (antibodies and IFN-gamma secreting cells-SC) in piglets derived from vaccinated sows and vaccinated at different weeks of age, namely 4, 6 and 8. The study has been carried out over three subsequent production cycles (replicates). At the start/enrolment, 46 gilts were considered at first mating, bled and vaccinated. At first, second and third farrowing, the dams were bled and re-vaccinated at the subsequent mating after weaning piglets. The matching piglets at each farrowing (first, second and third) were randomly allocated in 4 different groups (100 animals/group) on the basis of the vaccination timing: 4, 6 and 8 weeks of age. A fourth control/non-vaccinated group was also included. Piglets were vaccinated intramuscularly with 2 mL of one dose of a commercial PCV2a-based subunit vaccine (Porcilis® PCV - MSD Animal Health, Whitehouse Station, NJ, USA). Twenty animals per group were bled every four weeks from vaccination to slaughterhouse for the detection of PCV2 and PRRSV viremia, humoral and cell-mediated immune response (IFN- SC). Clinical signs and individual treatments (morbidity), mortality, body weight were recorded. In the first and second replicate, a weak natural PCV2 challenge, that did not result in PCVD, occurred at 17-20 weeks of age. All the vaccination schemes (4, 6 & 8 weeks of age) were able to induce seroconversion (no interference of MDA) but the highest titers of antibodies and IFN- SC were in pigs vaccinated at 6 weeks of age. In the third replicate, PCV2 natural infection occurred at 20 weeks and 100% of the control pigs showed a viral burden in their blood even higher than 107 in association with clinical signs referred to as PCVD. All vaccinated animals were protected and only few of them were viremic but the best performance either in term of immune reactivity, productivity and health status were observed in pigs vaccinated at 6 weeks of age. Overall, repeated PCV2 vaccination in sows at mating and the subsequent more homogeneous titers of antibodies at farrowing does not significantly interfere with inducing both humoral and cell-mediated immunity in their piglets after vaccination with the best performance obtained when vaccinating at 6-8 weeks of age.