The level of antibody by ELISA,immunsosuppressive effect baes on the response of birds to Newcastle disease vaccination and damage to bursa of Fabricius by IBD vaccination were studied. The efficacy of six different IBD vaccination schedules were studied using intermediate and intermediate plus strains of vaccines either alone or in combination. In vaccinated groups, the sero-conversion of the vaccine virus was noticed during fourth week, reaching to the peak between eight to twelve weeks of age in different groups. Afterwards, there was a gradual decrease in the titres, by the end of 20th week (maximum period tested). There was no significant difference in the titres of different treatment groups. However, all the groups showed titres above protective level during the entire period of study. There was significant difference in bursa body weight (B-BW) ratios of vaccinated groups in comparison with control group. Histopathological studies of bursal sections revealed depletion of lymphoid follicles, presence of cystic spaces, edema and hemorrhages. The birds vaccinated with hot strain of IBD vaccine showed metaplastic changes, presence of foam cells with pronounced interfollicular fibrosis. The bursal scores were maximum in the groups vaccinated with hot strains of IBD vaccines.

Outer membrane proteins (OMPs) of Pasteurella multocida strain P52 were purified by immunoaffinity chromatography (IAC) using pre-challenge serum from HS vaccinated cattle-calves. IgG antibody titers of pre-challenge sera from HS vaccinated calves surviving and succumbing to direct challenge with virulent culture were determined against formalized P52 cells, P52 crude cell lysate, and OMPs of P52 purified by IAC. It was observed that OMP antigens were involved with protective response in calves and indirect ELISA test using lAC purified antigens can be developed for in vitro potency determination of Haemorrhagic septicemia (HS) vaccines.