The aim of the studies was the use of Haemophilus somnus vaccine in the immunization of chickens to protect them against Salmonella infections by increasing the local cross-immunity of the alimentary tract. Broilers were immunized with a live vaccine administered in drinking water on the 1st and the 14,h day of life. The groups were as follows: H. somnus (24h broth culture, 109 cfu/ml); Salmonella typhimurium (live, attenuated vaccine, 1010 cfu/ml, TAD, Cuxhaven, FRG), and the control. The efficacy of the vaccines applied was assessed upon: bacteriological monitoring of gut and organs for the presence of Salmonella, results of challenge with S. enteritidis on the 10th day, following the second vaccination, and serological monitoring (specific antibodies -IgA, IgG and IgM in bile, serum and intestinal mucus by ELISA test). The results tndftate that the chickens' immunization with H. somnus oral vaccine protect them from infection with the virulent strain of S. enteritidis. On the 18lh day after the challenge no S. enteritidis was found in the cloaca and organs of the chickens immunized with H. somnus and S. typhimurium, whereas in the control group. S. enteritidis was isolated in 20 to 50% of the samples collected from the duodenum, liver and caecum. The serological examination showed that in immunized chickens, after the challenge a rapid, anamnestic response of IgA specific antibodies occurred in all the fluids examined (serum, bile and intestinal mucus). It indicates the protective role of local cross-reacting antibodies, induced by oral H.somnus vaccination.
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