SREEDEVI, B (Major)SUDHAKAR GOUD, K2016-12-202016-12-202003-09http://krishikosh.egranth.ac.in/handle/1/91637ABSTRACT The present study was taken up to evaluate the efficacy of different Infectious Bursal Disease (IBD) vaccines using different vaccination schedules employing different strains of IBD vaccines. The response to vaccination in terms of sero conversion, the extent of bursal damage and immunosuppression caused by these vaccines were studied. A total of 280 layer chicks were randomly divided into seven groups each consisting of 40 chicks. Six different IBD vaccination schedules were tested using different combinations of IBD vaccines. Group I was maintained as a control without giving any IBD vaccination. All the birds including control received Newcastle Disease (ND) vaccination as per the standard schedule. The serum samples were collected from all the groups at weekly intervals for 20 weeks (maximum period tested). The IBD antibodies were estimated using IDEXX - ELISA (Flockcheck) kit. A gradual decline of IBD maternal antibodies was noticed in the control group and the samples were found to be negative by sixth week of age. Vaccination of birds with IBD vaccines did not interfere with the decay of maternal immunity. In group II which received IBD vaccines at day old age, the immediate sero conversion was absent and the antibody titres raised only after subsequent vaccinations. The results of ELISA in other groups showed that, lowest titres were recorded during the third week after which the titres increased gradually reaching peak between eight to twelve weeks of age and a slight decline was observed by the end of 20th week. But they were all found to be above protective levels till 20 weeks of age. No significant difference was noticed between the titres of different treatment groups. The titres in group III which received an oil emulsion IBD vacccine after initial live virus priming also showed similar response in comparison to other groups. Significant difference was noticed in the bursa body weight (B-BW) ratios of IBD vaccinated groups in comparison with the control group. During third week of age, the B-BW ratios recorded were more in vaccinated birds while reduced B-BW ratios were recorded during fourth and fifth weeks in comparison with the control. Histopathology of the bursal sections revealed varying degrees of bursal damage in the vaccinated groups while the bursae collected from the control group were normal. Bursal lesion scores were calculated in terms of the lymphoid depletion in the follicles and were graded between 0 to 4. Highest bursal lesion scores were noticed in groups vaccinated with intermediate plus strain of IBD vaccines. The immunosuppressive effect of different IBD vaccines was evaluated in terms of response to ND vaccination. The results revealed that there was a gradual increase in the NDV-HI titres from third week onwards in all the groups including the control. But a moderate suppression of vaccine response was noticed in groups V, VI and VII which received either one or few doses of intermediate plus vaccines. But all the HI titres were found to be well above the protective level. Based on the results obtained in the present study it is concluded that even though live IBD vaccines caused significant bursal damage, the immunosuppression caused by these vaccines was only moderate. Hence, they can be used at the field level by selecting a least immunosuppressive strain. Vaccination of day old birds with IBD vaccines and usage of an oil emulsion vaccine in the early days of life did not confer any special advantage. Also no additional advantage was observed by giving a third dose of IBD vaccine after fourth week of age.enInfectious Bursal Disease ; IBD; VACCINATION; IMMUNITYThesis