SEROLOGY AND ISOLATION OF SALMONELLA SP. IN PIGS AT THE FINISHING SITE AND AT SLAUGHTER

Abstract

Studies assessing the Salmonella transmission chain in pig herds are the first step to start a control program.  The aims of this study were to compare the prevalence of Salmonella positive pigs at the beginning of the finishing phase and at slaughter, and to identify the possible sources of contamination in the farms. In three finishing farms, environmental swabs from the barns and from the feed silos were collected during the sanitary emptiness. Furthermore, samples of feces and blood from the animals on the day of housing; and aliquots from all feed lots were taken. At slaughter, blood, mesenteric lymph nodes (LM) and intestinal content (CI) were sampled. Blood samples were submitted to a S. Typhimurium ELISA-LPS test. All other samples were submitted to a Salmonella isolation protocol. Feed samples were also submitted to Polymerase Chain Reaction (PCR) targeting the invA gene. Feces samples from all pigs were Salmonella negative at the beginning of the finishing phase, in two farms seropositive animals were found. In two farms, residual environmental contamination was detected, and, in the third farm, one of the feed batches was Salmonella positive on the PCR assay. At slaughter, over 90% of the animals were positive on the ELISA-LPS test and, in all cohorts, a variable number (12%-92%) of carriers in LM and CI was detected. From this on, it was concluded that the finishing phase was critical for the amplification of Salmonella infection, and the residual environmental contamination in the farms as well as Salmonella positive feed batches were the probable infection sources.

KEY WORDS: Isolation, finishing and slaughter, Salmonella, serology, swine.