Vaccination of pigs reduces Salmonella Typhimurium numbers in a model mimicking pre-slaughter stress

In pigs, infection with Salmonella Typhimurium often results in the development of carriers that re-excrete the organism during periods of stress. Previous studies have shown that cortisol plays a significant role in the recrudescence of Salmonella Typhimurium and that re-excretion can be induced by injections of dexamethasone. This study evaluated whether a commercially available Salmonella Typhimurium vaccine was able to reduce Salmonella excretion in a model mimicking pre-slaughter stress. Pigs were randomly assigned to either vaccination or a control group and, 5 weeks later, were infected with Salmonella Typhimurium. Twenty-three days post infection, pigs were injected with dexamethasone to induce recrudescence and Salmonella Typhimurium numbers were determined. Salmonella loads were significantly lower in the ileum and colon and in the contents of the ileum and caecum in vaccinated pigs than in non-vaccinated pigs. In addition, significantly more Salmonella positive tonsil and colon samples were found in non-vaccinated pigs. Vaccination with an attenuated vaccine reduced but did not eliminate Salmonella Typhimurium in pigs in conditions mimicking pre-slaughter stress.