Abstract

Aim: Newcastle Disease (ND) remains a major threat to poultry production in Nigeria, despite routine vaccination. This study assessed antibody responses to different ND vaccination regimens and evaluated risk factors associated with ND outbreak occurrence in Southwestern Nigeria.
Methods: A purposive cross-sectional study was conducted from November 2024 to March 2025. Quantitative serological analysis using the Hemagglutination Inhibition (HI) test was performed on 1,714 serum samples from 102 farms across six states. A structured questionnaire assessed vaccination practices and farm management. Logistic regression was used to identify predictors of ND outbreaks. Analyses were performed in STATA version 17.
Results: Vaccination schedules included monthly (43.1%), bi-weekly (17.6%), bi-monthly (16.1%), weekly (13.7%), and irregular (11.8%). The geometric mean titre (GMT) varied significantly across farms (p < 0.01), with 63.7% of farms showing titres below protective levels. Farms with poor biosecurity had significantly higher odds of ND outbreaks (OR = 2.75; 95% CI: 1.68–4.52; p < 0.001). Using fewer than three vaccine doses was associated with increased outbreak risk (OR = 1.92; 95% CI: 1.14–3.24; p = 0.015). Cold chain failures (OR = 1.84; 95% CI: 1.06–3.17) and not using stabilizers (OR = 1.63; 95% CI: 1.02–2.62) were additional risk factors. Free-range poultry were mostly unvaccinated due to high cost (33%), poor access (42%), and administration difficulty (24%). Notably, 66.7% of farmers were unaware of any national ND vaccination schedule.
Conclusions: ND outbreaks are significantly associated with poor biosecurity, under-vaccination, and cold chain lapses. Strengthening vaccination protocol adherence, improved extension services, and routine seromonitoring are critical for ND control, particularly among smallholder backyard poultry farmers. It is also important to develop more effective control packages suited to the production and socio-economic context of backyard poultry farmers. This field-based evidence supports policy and practice improvements for enhanced poultry health in Nigeria.

Key words: Vaccination regimen, Seromonitoring, Newcastle Disease, poultry vaccination, Hemagglutination Inhibition (HI) Test, Antibody titre, Biosecurity.