Current research has implicated bovine lymph nodes as a potential source of Salmonella contamination of ground beef. Until recently, Salmonella cross-contamination of the carcass was believed to occur via the hide or the intestinal tract during slaughter. Many beef processing facilities have implemented effective food safety interventions to control this manner of contamination. Despite controls, Salmonella can be a contaminant of raw ground beef, and data indicates that bovine lymph nodes are protecting Salmonella from post-harvest interventions. Furthermore, it is not practically possible to completely remove all lymph nodes from a beef carcass, creating potential for contaminated lymph nodes to be incorporated into a grind and thus contaminate ground beef product.
With few post-harvest intervention strategies available, investigation of the efficacy of using pre-harvest interventions to control lymph node contamination was necessary. Currently, direct-fed microbials (DFM) are routinely fed as part of feedlot cattle diets, specifically Lactobacillus animalis (NP51) and Propionibacterium freudenreichii (NP24). Data — particularly on the high dose of 109 cfu/head/day — are available on the reduction of E. coli O157:H7 and Salmonella in the feces and on the hides of feedlot cattle being administered NP51 and NP24 in their diets (Brashears et al., 2002, 2003; Elam et al., 2003; Younts-Dahl et al., 2004, 2005; Loneragan and Brashears, 2005; Peterson et al., 2007; Stephens et al., 2007). These studies indicate feeding a DFM could also hold promise for the reduction of Salmonella presence and concentration within bovine lymph nodes.