In this study, the efficacy of a live-attenuated Salmonella Typhimurium vaccine administered to pregnant sows in the breeding herd was evaluated as a means of reducing the prevalence of Salmonella infection in growing and finishing pigs. The results suggest no significant difference between the prevalence of Salmonella (all serovars) in the two groups of sows and their offspring. The lymph node and meat juice collected from carcasses of offspring showed no significant difference between the two groups, but the prevalence of Salmonella was significantly lower in the caecum content from pigs born of vaccinated sows. The farm had a very low prevalence of S. Typhimurium, which may explain the failure to detect any effect of the vaccine, as the majority of Salmonella on this farm was S. Derby.