Salmonella status of pigs at slaughter--bacteriological and serological analysis

Apart from Salmonella monitoring of pig herds during the period of growth to evaluate the efficacy of control programmes, monitoring at harvest level is of relevance to assess the Salmonella status of fattening pigs and the associated risk of introducing Salmonella organisms in the slaughter process. Samples from 1830 fattening pigs were gathered at slaughter. Ileocaecal lymph nodes, rectal and caecal content as well as tonsils were collected for bacteriological examinations, and a part of the diaphragm pillar muscle was taken to gain meat-juice for serological analysis. Salmonella spp. was recovered from 13.8% of all pigs examined. Salmonella Typhimurium and Derby were the dominating serovars. The highest detection rates were found in caecal content followed by ileocaecal lymph nodes. By analysing both organs nearly 90% of all Salmonella positive pigs could be identified. Serological examination revealed 9.6% of the pigs as positive using a cut-off value of OD % ≥ 40. Only one quarter of all Salmonella positive pigs showed also a positive serological result. A reduction of the cut-off value does not necessarily result in a higher compliance between bacteriologically and serologically positive slaughter pigs. Detection of antibodies is useful to verify whether pig herds were previously exposed to Salmonella organisms. However, the Salmonella status of pigs at time of slaughter and the associated risk of dissemination of Salmonella organisms can only be assessed by bacteriological examinations which should include both lymph nodes and caecal content.