Comparison of the residual virulence of Newcastle disease vaccine strains V4, Hitchner B1 and La Sota.

The clinical response of 7-day-old chickens to Newcastle disease vaccine strains V4, B1 and La Sota administered by the aerosol method was used to study the residual virulence of the strains. Parameters used to assess the severity of the clinical response were the number of sneezes recorded and the weight gain of chickens in the 10 day test period. The demeanour of the chickens was also observed. Strain V4 was less pathogenic for chickens than strain B1 which was less virulent than strain La Sota. Statistically significant differences were recorded in weight gain and the number of sneezes detected in each group. An unexpected mild respiratory disease recorded in chickens dosed with strain V4 may have been associated with administration of virus as a fine particle aerosol.