Immunogenicity and safety of a livePasteurella anatipestifervaccine in White Pekin ducklings: Laboratory and field trials

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Abstract
Oral or aerosol administration of a live trivalent Pasteurella anatipestifer (PA) vaccine (sero‐types 1, 2 and 5) gave significant protection against homologous challenges in White Pekin ducklings. Vaccination of one‐day‐old ducklings by either method provided protection for at least 42 days of age (last challenge). The vaccine did not cause any untoward signs or mortality in one‐day‐old ducklings exposed to ten times the recommended dose. The vaccine strains did not revert to virulence on 10 back‐passages. However, they were reisolated from tracheas and sinuses of the contact‐exposed ducklings which were also resistant to challenge with homologous serotype. Feeding of chlortetracycline (0.044%) or sulphadime‐thoxine‐ormetoprim (0.02%) for first 2 weeks of age had no adverse effect on efficacy of the vaccine. The vaccine was found to be both safe and efficacious in field trials in which one‐day‐old ducklings were exposed by aerosol in the hatcher.