KEY TAKEAWAYS

• While there was no significant difference in Salmonella prevalence between dairy×beef and native beef cattle upon arrival at the feedlot, differences do emerge in fecal samples between breeds after they are finished in a feedlot.
• Intrinsic feedlot-specific variability has a more significant role in influencing Salmonella risk.
• The presence of Salmonella in fecal material and subiliac lymph nodes (SLNs) are minimally related; relying solely on fecal samples for Salmonella surveillance may not provide a comprehensive assessment.

BACKGROUND

Salmonella that colonize non-mesenteric, peripheral lymph nodes (PLNs) serve as a potential source of ground beef contamination, as these PLNs are generally encased within several centimeters of adipose tissue and are impervious to in-plant interventions designed to reduce pathogenic bacteria on the carcass surface. While Salmonella uptake in PLNs has been the subject of considerable research in the past decade, relatively little is known regarding the dynamics of uptake and acquisition of Salmonella by the PLNs. It was observed in a recently funded study through NCBA, a contractor to the Beef Checkoff, that Salmonella prevalence was higher in the subiliac lymph nodes (SLNs) (25.25%) than in the colon (19.5%) or liver (19%) tissue samples at slaughter. Deep serotyping found that across 25 paired samples, the serotype profiles were highly dissimilar between colon and lymph nodes in 76% samples. This supports published data demonstrating that analysis of fecal/GI Salmonella is not useful for estimating Salmonella profiles in lymph nodes. Recently, human outbreaks of Salmonella serotypes Heidelberg and Newport in beef products have been linked to dairy calves or cows. Concomitantly, over the past decade, it has become increasingly common to raise dairy×beef calves for entry into the feedlot production systems. Generally, dairy×beef calves are separated from their dams at birth and raised in hutches at calf ranches, which makes preparation for entry into the feedlot markedly different from that of conventional beef breed calves that are weaned for several weeks. The complexity of the dairy×beef production system could inherently make these cattle more susceptible to shedding Salmonella. Along each segment of production from dairy farm to calf ranch management to the feedlot, these animals are stressed, commingled, and exposed to a host of environmental factors. Constant physiological stress might predispose these cattle to sequestration of Salmonella by PLN. Previous research has reported that increased stress suppresses components of the immune system, leading to an increased susceptibility to infection, should a pathogen be present. During periods of host stress the neuroendocrine systems release hormones such as epinephrine, norepinephrine, and cortisol to mediate the stress response. Salmonella can exploit the neuroendocrine stress response as a signal for growth and increased virulence and by doing so, promote pathogen survival through increased dispersal in the host. Hence, it is plausible that cattle which are repeatedly exposed to pre-harvest stressors may exhibit an increase in Salmonella prevalence in PLNs at slaughter. Dairy×beef calves represent approximately 15-20% of beef cattle in the United States. Therefore, to continue to improve food safety in beef production, it is critical to determine the influence that dairy×beef production has on Salmonella for the beef industry. The objectives of this study were to assess the difference in Salmonella prevalence of dairy×beef vs. native cattle upon arrival at a commercial feedlot, and to probe the association between dairy×beef genetics and Salmonella prevalence and quantification within SLNs of commercially finished beef carcasses.