13 October 2026
Researchers in Japan have established protective maternal antibody thresholds against fowl adenovirus (FAdV) serotypes 1, 2, and 8b, demonstrating that a prototype trivalent inactivated vaccine administered to breeders can provide sustained, multi-serotype passive protection to progeny for over 15 months.
Fowl adenoviruses (Aviadenovirus, FAdVs) pose a significant threat to commercial poultry production worldwide, causing substantial economic losses through distinct clinical syndromes. Because FAdV infections can affect broilers during their first week of life, and both horizontal and vertical transmission occur, vaccinating day-old chicks is often impractical. Protection during this critical period therefore depends largely on maternally derived antibodies (MDAs) transferred from breeder hens through the egg yolk.
A major challenge in FAdV control is the limited cross-protection among antigenically distinct serotypes, making serotype-specific immunity essential. To quantify the relationship between maternal antibody titers and protection in chicks, researchers evaluated breeder vaccination, maternal antibody transfer kinetics, and progeny resistance to challenge with virulent field strains (FAdV-1 Aichi4196-1, FAdV-2 P-7A, and FAdV-8b IW20-2).
Progeny chicks with maternal virus-neutralization (VN) titers below 1:8 experienced mortality rates of 21%–51% following virulent challenge. A titer of 1:8 prevented mortality, but clinical disease and pathological lesions were still observed. Titers of ≥1:16 for serotypes 1 and 2, and ≥1:8 for serotype 8b, completely prevented clinical signs and gross pathological lesions while maintaining normal body-weight gain.
The transfer efficiency of maternal neutralizing antibodies from hen serum to day-old chicks ranged from 25% to 40% across the three serotypes. Based on the conservative lower transfer estimate of 25%, breeder hens must maintain serum neutralization titers of at least 1:64 to ensure that their progeny hatch with protective titers of ≥1:16.
Defining these quantitative antibody thresholds provides field veterinarians, vaccine manufacturers, and quality-control laboratories with a practical immunological benchmark. Serological monitoring can help determine whether breeder flocks are transferring sufficient passive immunity to protect broilers during early life.
Furthermore, the researchers demonstrated that the prototype trivalent inactivated vaccine maintained protective antibody titers for over 15 months without evidence of antigenic interference, supporting the feasibility of multivalent breeder vaccination strategies against diverse FAdV serotypes.
Izutsu et al. (2026). Maternal immunity to fowl adenovirus in chicks derived from vaccinated hens. The Journal of Veterinary Medical Science, Advance Publication, Accepted October 1, 2026; Published online October 13, 2026.
