Fecal shedding of Salmonella by gilts before and after introduction to a swine breeding farm

Fecal shedding of Salmonella serotypes was studied in two groups of gilts introduced to a swine breeding farm from a gilt-development farm. Fecal samples were collected from individually identified gilts (121 from group 1 and 81 from group 2) at the gilt farm before transport, and after arrival at the breeding farm (11 days post-arrival for group 1; 4 and 12 days post-arrival for group 2). In both groups of gilts, prevalence of fecal samples positive for Salmonella was lower (<4%) in samples collected at the gilt farm prior to transport than in samples collected after arrival at the breeding farm (>20%; P <.001). Changes in serotype profiles in the two groups suggested that both increased shedding by carrier animals after transport, and that new infections acquired after arrival contributed to the increase in prevalence. Regardless of mechanism, the marked increases observed indicate that high replacement rates and external sourcing of gilt replacements may contribute to the maintenance of Salmonella infections in some herds.