Sub-iliac lymph nodes at slaughter lack ability to predict Salmonella enterica prevalence for swine farms

The aim of this study was to assess the value of deep systemic sub-iliac lymph nodes collected at slaughter as predictors of Salmonella prevalence in live hogs. An observational study was conducted on 24 farms from September 2006 to February 2009. At least one cohort of market-weight pigs was visited for each farm. Within each cohort, 30 farm fecal samples on farm and 30 sub-iliac lymph nodes from matched pigs at slaughter were collected. Samples were cultured for Salmonella enterica and serotyped by conventional methods. Overall, 3.4% (51 of 1490) of farm feces and 0.06% (1 of 1739) of sub-iliac lymph nodes were Salmonella positive; 71.4% (15 of 21) of farms had at least one positive fecal sample, and 4.2% (1 of 24) had at least one positive sub-iliac lymph node. The median within-farm prevalence of Salmonella in farm fecal samples was 1.7%, ranging from 0% to 38.3%; for sub-iliac lymph nodes the median was 0%, ranging from 0% to 1.1%. The median within-cohort prevalence in farm fecal samples was 0%, ranging from 0% to 43.3%; for sub-iliac lymph nodes the median was 0%, ranging from 0% to 4%. The predominant serotype detected was Derby, followed by Anatum and Typhimurium (Copenhagen). Salmonella Braenderup was recovered from the sub-iliac lymph node. The low detection rate of Salmonella in sub-iliac lymph nodes (0.06%) limits its usefulness as a dependable predictor of Salmonella contamination originating on farm (3.4%).