Abstract   

    The study was conducted to test the pathogenic effect of six commercially available infectious bursal disease (IBD) vaccines claimed to be intermediate in their pathogenicity. Three week old chickens were inoculated with these vaccines. The pathogenic effects of the IBD vaccines were evaluated by hemorrhages on the thigh and breast muscles, bursa weight to body weight ratio and virulence; two of the strain were found to be highly virulent; two others were moderate and two could be classified as mild.    

Key words: Gumboro, Vaccine, Pathogenicity