An Ulster 2C strain-derived Newcastle disease vaccine: efficacy and excretion in maternally immune chickens.

Efficacy and excretion of an Ulster strain-derived Newcastle disease (ND) vaccine (Poulvac NDW Broiler) were examined in maternally immune chickens. The vaccine was effective in broilers following coarse spray or aerosol (Atomist) application at one to 10 days of age. Immunity did not differ significantly from immunity following vaccination with a La Sota type vaccine. Also, combined spray application of NDW- and infectious bronchitis (IB) (Poulvac IB primer) vaccine at 1-day-old, resulted in sufficient protection against challenge with both virulent ND and IB virus. In layers the vaccine was less immunogenic, requiring large doses to induce sufficient protection in chickens with maternal antibodies. In layers this may make the vaccine economically non-viable. Atomist vaccination using economically justified doses, was effective after maternal antibodies had waned. Clinical signs of vaccinal reaction were not observed in layers. In broilers respiratory signs of vaccinal reaction were absent after spray-application and were very slight following Atomist administration. Body weight gain was temporarily depressed, but significantly less than following vaccination with a La Sota type vaccine. Following vaccination, vaccine virus could be recovered from cloacal content and trachea up to 15 and 8 days respectively.