Use of an attenuated live Salmonella Typhimurium vaccine on three breeding pig units: A longitudinal observational field study

• Parenteral administration of a live Salmonella Typhimurium vaccine to dams in the context of commercial breeder or breeder-finisher units was associated with rapid control of clinical salmonellosis.
• Over one to two years, sustained reductions in the shedding of Salmonella Typhimurium, and a closely-related monophasic variant, were observed.
• The maternal vaccination was associated with improved Salmonella status in all age groups.
• Evidence for control of other (non-Typhimurium) Salmonella serovars was not seen.

The study examined the effects of a licensed live Salmonella Typhimurium vaccine, administered to sows and gilts on three commercial pig units experiencing clinical salmonellosis associated with S. Typhimurium or its monophasic variant. After vaccination, clinical salmonellosis resolved and shedding of S. Typhimurium declined markedly and persistently on all breeding or breeding-finishing units, during the one- to two-year monitoring period. On two finishing units supplied in part by one of the vaccinated herds, pigs from the vaccinated herd were less likely to shed Salmonella than those from non-vaccinating herds, and Salmonella counts in faeces were also lower from the vaccine-linked animals. Non-Typhimurium Salmonella serovars were isolated typically in fewer than 10% of samples, and showed no clear temporal changes in frequency. Vaccination of dams alone with S. Typhimurium was associated with reduced shedding of closely-related serovars among all age groups in this commercial setting.