Comparative evaluation of HVT-vectored vaccines efficacy against Newcastle disease in broiler chickens

HVT-vectored Newcastle disease (ND) vaccines are widely used in broiler production, but direct commercial-field comparisons among licensed products remain limited. The aim of this study was to compare three commercial HVT-vectored ND vaccines used in broilers within the same live ND vaccination program by assessing vector genome detection in spleen samples and humoral response kinetics. Three similar broiler groups from a large commercial operation received one coded HVT-vectored vaccine at hatch (Vaccine A, Vaccine B, or Vaccine C), followed by Clone 30 spray on day 1 and La Sota on day 12. Spleen impression samples collected on FTA cards at 28 days (10 per group) were tested by qPCR targeting HVT SORF1. Blood samples collected at 21, 28, and 42 days (20/group/time point) were examined by hemagglutination inhibition (HI) and ID.Vet ELISA-F. Because the archived dataset contained group summaries rather than bird-level continuous raw values, inferential analysis was limited to qPCR positivity and seropositivity counts. Vaccine B showed the highest qPCR positivity in spleen samples at day 28 (90.0%), followed by Vaccine A (70.0%) and Vaccine C (40.0%) (overall chi-square p = 0.058). Seroconversion was also fastest in Vaccine B, with seropositive proportions of 90%, 100%, and 100% at days 21, 28, and 42, respectively, versus 60%, 75%, and 90% for Vaccine A and 35%, 45%, and 70% for Vaccine C. Overall differences in seropositivity were significant at each time point. The results indicate that the evaluated HVT-vectored vaccines were not biologically interchangeable under the same field program and that spleen qPCR can complement routine serology in comparative field assessment of HVT-based ND vaccination.