RESUMEN
Intermediate plus live strain infectious bursal disease virus (IBDV) vaccines are used to control IBDV endemic infections in India. In the present study, immunopathological changes induced by commercial infectious bursal disease live vaccines with different immunization regimes were compared. A total of days old 108 Cobb broiler chicks were randomly divided into five groups with 24 chicks each in groups I, II, III and 18 chicks each in group IV and V. Group I served as control I (no immunization) and group II and III chicks were immunized with a single dose of vaccines 1 and 2 on 17th day of age (DOA), respectively. The group IV and V chicks were immunized with vaccines 1 and 2, respectively with primary dose on 17th DOA followed by booster dose on 24th DOA. Both intermediate plus live vaccines produced gross and histopathological lesions in lymphoid organs (bursa of Fabricius, thymus, spleen and caecal tonsils). Increased CD4 + , CD8 + T cells in affected bursa of Fabricius was evidenced by immunohistochemistry. Further, up-regulation in relative mRNA expression of IFN-γ, IL-1ß and IL-6 were observed in bursa of Fabricius of treated birds, with maximum alteration particularly on 14th day post single immunization and 7th day post booster immunization. The findings suggest that single immunization regime on the 17th day of age showed immunization equivalent to booster immunization with lesser lesions, therefore, may be practiced and promoted in the field conditions for the better economic returns and animal welfare.