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Background  For satisfactory  Salmonella  control, good biosecurity along the pork production chain is crucial, although additional control measures on-farm need to be considered. This study evaluated the effect of two potential control measures against the spread of  Salmonella  Typhimurium via a transmission experiment with 56 piglets (3–15 weeks of age): two groups were orally vaccinated with 10 7  - 10 8  Colony Forming Units (CFU)/2 mL of a new attenuated  Salmonella  Typhimurium vaccine ‘Salmoporc-∆ rfaJ ’ with DIVA capacities (Differentiation between Infected and Vaccinated Animals) ( n  = 2x16); the feed of one group was additionally supplemented with coated calcium-butyrate salt. Two weeks post vaccination, four pigs per group were orally challenged with 10 7  CFU/2 mL of a  Salmonella  Typhimurium strain 112910a. Both groups were compared with a positive (challenged/untreated;  n  = 16) and negative (unchallenged/untreated;  n  = 8) control group. Until six weeks post challenge, blood, individual faecal and finally tissue samples were examined. Adjusted transmission ratios ‘R a ’ were estimated, based on the challenge strain isolation from faecal and/or tissue samples.    Results  In both intervention groups, R a  values were lower compared to the positive control group, although these differences were not significant. In the combination group DIVA vaccine + coated butyrate, less non-challenged contact animals excreted  Salmonella  and less tissue samples were found  Salmonella -positive in all pigs, when compared to the positive control group ( P  < 0.01). Seroconversion was detected in none of the vaccinated animals before challenge, when using a commercial lipopolysaccharide (LPS) ELISA targeting only  Salmonella  O-antigens, deleted in this vaccine. This was in contrast with an in-house whole-cell ELISA testing for various  Salmonella  antigens, in which  Salmonella -specific antibodies were found pre-challenge in the serum of the vaccinated pigs.    Conclusions  Both interventions showed a limited, non-significant reduction of  Salmonella  transmission between piglets. They may have applications towards  Salmonella  control and surveillance. Firstly, the number of  Salmonella  excreting contact pigs was significantly lower in the group where vaccination was combined with coated calcium-butyrate salt in the feed; secondly, the new vaccine confirmed its DIVA capacity. Therefore, these interventions merit further research with larger sample sizes, to optimize their use for  Salmonella  programmes.

Effect of a DIVA vaccine with and without in-feed use of coated calcium-butyrate on transmission of Salmonella Typhimurium in pigs