Comparison of the immunogenicity of Newcastle disease virus strains V4, B1 and La Sota in chickens. 1. Tests in susceptible chickens.

The immunogenicity of the Australian Newcastle disease virus (NDV) strain V4 was compared with that of the International reference preparation of Hitchner B1 and a commercial La Sota strain. Immunity was assessed serologically using the log mean HI titres 21 days after immunisation, the percentage of birds in each group which developed titres greater than 2(3) and their resistance to graded challenge doses of the virulent Herts 33/56 strain of NDV. These tests showed that the V4 strain was significantly less immunogenic (P less than 0.01) than the B1 or La Sota strains when administered intraocularly (eye drop) or by aerosol methods. When given in the drinking water V4 induced a better immunity (P less than 0.01) than the B1 strain in one of 2 experiments.