Abstract

    This project was carried out to study the comparative immunosuppressive effects of three different Gumboro live vaccine strains on Newcastle disease (NO) vaccination. A total of 100 chicks were divided into four equal groups (A, B, C and O). Birds of all the groups were vaccinated against ND on 5^th and 21^st day of age. Specific Gumboro vaccine strain was given to specific group at 14^th and 28^th day of age. Group A, Band C were vaccinated with 228-E, D- 78 and Bursine-2, respectively, while group D was kept as control. Immune organs including bursa, thymus and spleen were examined for their gross and, histopathological changes, before and after Infectious Bursal disease (IBO) vaccination. For this purpose, these organs were collected at 13^th, 17^th and 31^st days of age. At 13^th day (before 1BD vaccination) no gross and histopathological lesions were observed in any bird of any group. At 17^th  and 31^st  day, severe lesions were noted in group A, moderate lesions in group B, mild lesions in group C and no lesions were observed in immune organs of group D. Haemagglutination inhibition (HI) test showed that 228-E vaccine strain, (group A) was highly immunosuppressive, D- 78 vaccine strain (group B) was less immunosuppressive while Bursine-2 vaccine strain (group C) was least immunosuppressive. No humoral immunosuppression was observed in unvaccinated control group D. This study suggests the use of Bursine-2 strain of IBD vaccine in a flock having risk of ND infection, as it has least immunosuppressive effect against ND vaccination.