Salmonella carriage in peripheral lymph nodes and feces of cattle at slaughter is affected by cattle type, region, and season

Authors: Wottlin, Lauren; EDRINGTON, TOM - Diamond V Mills, Inc; Anderson, Robin

Submitted to: Frontiers in Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2022
Publication Date: 3/21/2022
Citation: Wottlin, L.R., Edrington, T.S., Anderson, R.C. 2022. Salmonella carriage in peripheral lymph nodes and feces of cattle at slaughter is affected by cattle type, region, and season. Frontiers in Animal Science. 3(1). Article 859800. https://doi.org/10.3389/fanim.2022.859800.
DOI: https://doi.org/10.3389/fanim.2022.859800

Interpretive Summary: Salmonella is occasionally found in retail beef, and it is thought that this happens from cattle lymph nodes with Salmonella inside them getting included in the ground beef. Contamination sometimes happens if a small amount of the animal’s feces gets on the carcass during the harvest process. In this study, 1,840 fecal samples and 1,550 subiliac lymph nodes (LN) were collected from cattle sourced from 5 different production systems, across 5 climate regions, in each of 3 seasons (summer, fall, winter) to better understand Salmonella inputs into commercial cattle slaughterhouses. Cattle types were cull beef cattle, cull dairy cows, conventional and all-natural feedlot cattle, and grass-finished cattle. Fecal samples and LN were analyzed for presence of Salmonella, and a small group of samples were serogrouped and tested for antimicrobial resistance. Conventional feedlot cattle had the highest LN Salmonella concentrations, while cull dairy cows had the highest concentration in the fecal samples. Conventional feedlot cattle and cull dairy cows had the highest Salmonella prevalence in both LN and feces, while all-natural feedlot cattle had the lowest prevalence. The Salmonella burden was the lowest for all cattle types during winter compared to warmer seasons. Prevalence of Salmonella in both feces and LN was highest in climate region 4 (hot-dry), compared to the other regions. Only 21 of 50 Salmonella isolates examined for antimicrobial susceptibility were identified as multidrug resistant (MDR); cull dairy cows were 48% of MDR, cull beef cattle were 38%, and conventional feedlot, grass-fed, and all-natural feedlot cattle were each 4.8%. These results show that different production schemes, seasons, and climate regions affect which cattle are most likely to bring Salmonella to the slaughterhouse, making it easier for producers to make better decisions and more easily understand risk.

Technical Abstract: Salmonella is a significant food safety concern in commercial beef production, and some contamination is thought to occur by inclusion of Salmonella-infected peripheral lymph nodes in ground beef and through fecal contamination. Surveillance in processing plants assists producers and packers in risk management of Salmonella by understanding seasonal trends and risks associated with different types of cattle. In this study, convenience samples of feces (n = 1,840) and subiliac lymph nodes (LN; n = 1,550) were collected from cattle sourced from 5 different production systems, across 5 geographic regions with different climates, in each of 3 seasons (summer, fall, winter) to better characterize Salmonella inputs into a single commercial cattle processing facility. Cattle types consisted of cull beef cattle, cull dairy cows, conventional and all-natural feedlot cattle, and grass-finished cattle. Fecal samples and LN were cultured quantitatively and qualitatively for Salmonella, and select isolates were serogrouped and screened for antimicrobial resistance. Conventional feedlot cattle had the highest LN Salmonella concentrations (1.17 log10 CFU/g LN) in this data set, while cull dairy cows had the highest fecal Salmonella concentrations (1.96 log10 CFU/g feces). Conventional feedlot cattle and cull dairy cows had the greatest Salmonella prevalence in both LN (32 and 18%, respectively) and feces (37 and 49%, respectively), while all-natural feedlot cattle had the lowest prevalence in the LN (3%) and feces (7%). As expected, Salmonella prevalence and concentration was lowest for all cattle types during winter compared to warmer seasons. When examined by climate region, a greater Salmonella prevalence in both feces and LN was observed in climate region 4 (hot-dry), than the other regions. Only 21 of 50 Salmonella isolates examined for antimicrobial susceptibility were identified as multidrug resistant (MDR); cull dairy cows were responsible for 48% of MDR isolates, cull beef cattle were responsible for 38%, and conventional feedlot, grass-fed, and all-natural feedlot cattle were each responsible for 4.8%. These results indicate that different production schemes, seasons, and climate regions may influence which cattle are most likely to introduce Salmonella to the abattoir, allowing for greater risk awareness during the slaughter process.