Appraisal of Day-Old Vaccination with Recombinant HVT-IBD-ND vaccine versus challenge with Very Virulent Infectious Bursal Disease (vvIBDV) In Broiler Chickens

Very virulent Infectious bursal disease (vvIBD) is a highly contagious disease of young chickens and still causing devastating economic losses in the Egyptian poultry industry consists of high mortality alongside with severe bursal damage and immunosuppression. This study aimed to assess the effectiveness of day-old vaccination with rHVT-IBD-ND vaccine against challenge with vvIBDV in broilers at 23 days of age. Four groups (N=30) were present in this study in which G1 (Vaccinated challenged), G2 (Vaccinated non-challenged), G3 (non-vaccinated challenged) and G4 (Negative control). Results revealed that absence of clinical signs; mortalities and gross lesions in G1, G2 and G4 compared to G3 which suffered from moderate clinical symptoms and the mortality were (6.6%). Moreover, the bursal body weight ratio (BBR) and bursal index (BI) were significantly reduced (p ≤ 0.01) at 7 dpc in G3 (0.55 & 0.37) less than G1 (1.45 & 0.79) respectively. The serological immune response in the vaccinated groups (G1 and G2) was significantly higher (p ≤ 0.01) than in non-vaccinated groups (G3 and G4) at 7 dpc and the mean ELISA titers were (13092, 12157, 6230 and 750) in G1, G2, G3 and G4, respectively. In addition, Histopathological examination revealed a significant reduction in the bursal lesions and mean severity index in G1 which recorded MLS of (1.5) in comparison with G3 significantly higher MSI (2.5). based on the results of the current study, it could be concluded that vaccination of broiler chickens with rHVT-IBD-ND vaccine at one-day-old provides complete clinical protection against vvIBDV beside partial protection from bursal tissue damage.