The effects of vaccine strain, route of administration of IB vaccine and revaccination on egg production and egg quality in laying hens

Different vaccination protocols for infectious bronchitis (IB) virus were administered to Isa Brown laying hens. Half the birds were revaccinated regularly during lay whereas the other birds were not vaccinated beyond 14 weeks of age. Body weight, production, blood haematocrit and plasma electrolyte concentrations were not affected by vaccination treatment. However, egg and egg shell quality differed between birds which were revaccinated regularly and those which were not. In general, egg shell quality was better in the birds which were not revaccinated at regular intervals. The birds which were vaccinated initially with the A3 vaccine tended to have lower albumen height and Haugh Units than the other treatment groups. The IB antibody titres were greatest at 6 and 16 weeks for both revaccinated and non-revaccinated birds. However, regular revaccination of birds beyond 14 weeks of age had no significant effect on IB antibody titre levels. These results suggest that there may be no advantage in regular vaccination of birds for IB, provided that birds have been properly vaccinated during rearing. However, more information is required about the correlation between blood IB titre levels and protection against intercurrent IB infection before recommendations can be made to the Australian industry.