Examination of the relationship between Salmonella contamination in pre-harvest environments and contamination of bovine peripheral lymph nodes

Bovine peripheral lymph nodes (PLNs) contained within adipose tissue, have been identified as a potential reservoir for Salmonella enterica in beef carcasses, and maybe a source of contamination of beef products. Recent studies suggest that the presence of Salmonella in cattle environments and on cattle hides provides the opportunity for Salmonella to gain entry to LNs via breaks in the skin such as insect bites and wounds. Once located within the lymphatic system, many Salmonella have the ability to persist or even thrive, without obvious negative impact on cattle health and performance. Furthermore, at harvest Salmonella located within LNs are protected from carcass antimicrobial interventions. Accordingly, there is a perceived need to identify pre-harvest measures for preventing Salmonella entry into this niche. To address this need, methods for determining Salmonella prevalence and levels in feedlot settings were evaluated with the goal of identifying reliable “predictors” of Salmonella prevalence. Analysis of feedlot environmental samples including pen surface material, tank water, feed and flies, suggests that high levels of Salmonella in tank water and measureable levels in feed are good indicators of high levels of Salmonella in a feedlot. Given the ease of collection and processing of these sample types, they represent good candidates for reliable “predictors” of feedlots that may benefit from a Salmonella intervention. The challenges and opportunities inherent in identifying viable pre-harvest intervention strategies will also be discussed.