Use of a live attenuated Salmonella enterica serovar Typhimurium vaccine on farrow-to-finish pig farms

•An attenuated S. enterica serovar Typhimurium vaccine was investigated in three pig herds infected with S. Typhimurium.•Vaccinated groups had less S. enterica-excreting pigs, lower S. enterica-specific mean antibody titres and higher weight gain.•In two herds, proportions of S. enterica-positive ileocaecal lymph nodes and caecal contents at slaughter were lower in vaccinated groups•Vaccination reduces S. enterica shedding, but results are variable and with possible persistence of the vaccine strain in tissues.

Salmonella enterica infection in pigs is economically important and poses a zoonotic risk. In this study, the efficacy of an attenuated S. enterica serovar Typhimurium strain was evaluated in three farrow-to-finish pig herds. In each herd, 120 piglets were vaccinated orally at 3 and 24 days of age, while 120 piglets served as unvaccinated controls. Faeces, ileocaecal lymph nodes and caecal contents were examined for S. Typhimurium by isolation and serum was analysed for antibodies against S. Typhimurium by ELISA. All pigs were weighed at pre-weaning and slaughter to determine daily weight gain. In vaccinated pigs prior to slaughter, significantly fewer animals excreted S. enterica, there was a significantly lower S. enterica-specific mean antibody titre and there was a significantly higher mean daily weight gain compared to unvaccinated controls. In two herds, there were significantly lower proportions of S. enterica positive ileocaecal lymph nodes and caecal contents at slaughter between the vaccinated and control groups, but this difference was not significant across all three herds. S. enterica with the same auxotrophic characteristics and genotype as the vaccine strain was isolated from several samples of faeces, ileocaecal lymph nodes and caecal contents from vaccinated pigs. These findings indicate that vaccination with an attenuated S. Typhimurium strain reduces S. enterica shedding, but the reduction is not consistent and the vaccine strain may persist in tissues.