The use of a live Salmonella bivalent vaccine for decreasing the circulation of salmonellae in a poultry plant

: S. typhimurium (expressing antigen 09 of S.dublin) recombinant vaccine strain was tested at a large poultry-breeding farm under the conditions of permanent circulation of salmonellae. The oral immunization of laying hens in three administrations with doses of 5 x 10(8), 5 x 10(9) and 5 x 10(9) microbial cells induced an increase in titers of antibodies only to group D salmonellae, while in immunized chickens (each receiving a dose of 3 x 10(8) microbial cells) antibodies to both group B and group D salmonellae were detected. The vaccination of laying hens and chickens produced a protective effect due to the development of immunity and the decrease of Salmonella contamination of eggs laid by immunized hens, thus reducing the risk of infection at incubator stations. Total mortality during the first 3 months of life was essentially lower (p < 0.001) among immunized chickens (4.41 +/- 0.09%) than in the control group of nonimmunized chickens (5.91 +/- 0.10%).