Multivalent fowl Adenovirus-Newcastle disease vaccine: comprehensive evaluation in SPF and commercial broiler breeders.

Abstract

BACKGROUND: Inclusion body hepatitis (IBH) and Newcastle disease (ND) impose substantial economic burdens on global poultry production, with combined annual losses exceeding $3&#xa0;billion worldwide. Current vaccination strategies requiring separate immunizations increase handling stress and operational costs. OBJECTIVE: To evaluate immunogenicity, cross-neutralization patterns, protective efficacy against virulent challenge, maternal antibody transfer, and commercial field performance of a novel multivalent inactivated vaccine containing fowl adenovirus (FAdV) serotypes 2, 8a, 8b, and 11 combined with Newcastle disease virus (NDV). METHODS: Two randomized, blinded, placebo-controlled trials were conducted: SPF trial (n&#x2009;=&#x2009;200, Egypt) and commercial field trial (n&#x2009;=&#x2009;120,000, Saudi Arabia). The multivalent vaccine contained inactivated FAdV serotypes 2, 8a, 8b, and 11 plus NDV strains, administered at 10 and 16 weeks of age with 24-week monitoring. RESULTS: Vaccination induced robust antibody responses with FAdV ELISA geometric mean titers (GMT) reaching 22,847 (95% CI: 18,245&#x2009;-&#x2009;28,589) at weeks 4-6 post-primary vaccination, with peak anamnestic response of 28,945 (95% CI: 23,186&#x2009;-&#x2009;36,115) at week 8 following booster (p&#x2009;<&#x2009;0.001) and NDV hemagglutination inhibition titers of 9.8 log&#x2082; (95% CI: 8.4-11.4) (p&#x2009;<&#x2009;0.001). Challenge studies demonstrated 96.7% protection against FAdV-2 (species D) (29/30 vaccinated vs. 6/30 controls; Fisher's exact p&#x2009;<&#x2009;0.0001) and 100% protection against NDV (30/30 vs. 0/30). Maternal antibody transfer efficiency was 68.6% for IBH and 81.7% for NDV, with half-lives of 4.2 and 4.8 days respectively, providing 24-28 days and 21-24 days protection in progeny. Commercial field trial (120,000 birds) demonstrated 94.2% reduction in IBH mortality with 3.47:1 return on investment. CONCLUSIONS: The multivalent IBH-NDV vaccine provides comprehensive immunological protection and consistent field efficacy. Although the cross-neutralization assay included representative serotypes, broader testing across additional field isolates is warranted to further define cross-protective breadth. Cross-neutralization analysis confirms the necessity of multivalent formulations due to type-specific immunity patterns, supporting implementation for integrated disease control in commercial broiler operations. This study provides a detailed evaluation of a quadrivalent FAdV-NDV inactivated vaccine demonstrating efficient maternal antibody transfer in broiler breeders.