Improvement of the efficacy of IB spray vaccinations in layers: a field experiment

The efficacy of spray vaccination against Infectious Bronchitis (IB) in rea ring layers, was examined in 12 flocks housed on 2 farms. For this purpose the vaccine was prepared with substantially more water than is commonly use d in practice and was carefully sprayed in the direction of the animals. Single vaccination at 2 weeks of age resulted in mean (2)log HI titres of o nly 3 to 4 at the end of the rearing period (16 weeks), whereas two vaccina tions yielded titres of 6 to 7. Upon a third vaccination, titres increased up to 7 to 9, individually even reaching 11. These titres are distinctly hi gher than the mean level in the Netherlands. None of the flocks showed clin ical symptoms of IB, neither during rearing, nor in the laying period, exce pt one. For unknown reasons, this flock showed a poor serological response after three vaccinations and subsequently experienced clinical IB at the st art of the laying period. It is concluded that administration of live IB vaccines as described in thi s study, deserves large scale practice, because it will then become clear w hether this procedure contributes to a better IB prevention or not.