Protective effect of oral administration of killed Haemophilus paragallinarum serotype A on chickens.

Orally administered bacterin of killed Haemophilus paragallinarum effectively induced production of serum hemagglutination-inhibition antibodies in chickens, and all immunized chickens were protected from subsequent infection. Although one intramuscular dose of 10(8) cells adjuvanted with aluminium phosphate gel (equivalent to commercial vaccine) induced protective immunity, two oral doses of 10(10) cells each with no adjuvants were required to induce effective immunity.