Decline of Maternal Antibodies Against Swine Influenza a and PRRS in Piglets From Different Sow Vaccination Programs

The primary objective of this study was to evaluate the effect of sow influenza vaccination timing on the persistence and decay of maternally derived antibodies (MDAs) against swine influenza A virus (IAV-S) in piglets. PRRSV antibody dynamics were additionally assessed to provide contextual information on maternally derived antibody decline and post-vaccination seroconversion under the same herd conditions. A total of 200 piglets (20 per group at each of five time points: days 5, 28, 42, 56, and 70) were sampled in a cross-sectional design. Serum antibodies against IAV-S and PRRSV were measured using commercial ELISA assays. Piglets born to sows vaccinated against IAV-S three weeks before farrowing (Group A) exhibited higher and more consistent MDA titers compared to those from sows vaccinated four months earlier (Group B). At day 56, 75% of piglets in Group A and 60% in Group B remained seropositive for IAV-S. By day 70, seropositivity declined to approximately 40–45% in both groups. A marked decline in antibody levels was observed over time, with a significant proportion of piglets becoming seronegative by eight weeks of age. For PRRSV, antibody levels declined until day 42 and increased thereafter following piglet vaccination, indicating successful induction of active immunity. These results highlight thecritical role of sow vaccination timing in shaping MDA kinetics and the need to align piglet vaccination strategies accordingly. Furthermore, they emphasize the necessity of integrated control approaches, beyond vaccination alone, to effectively manage PRRSV and IAV-S transmission in endemically infected herds.