Salmonella carriage in peripheral lymph nodes and feces of cattle at slaughter

Salmonella represents a primary food safety concern in retail beef, and some contamination is thought to occur through fecal contamination of the carcass and inclusion of contaminated lymph nodes in ground beef. Surveillance in processing plants assists producers and packers in risk management of Salmonella by understanding seasonal trends and risks of differing cattle types. In this study, fecal samples (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 and 3 seasons to better characterize trends in Salmonella burden. Cattle types were cull beef, cull dairy, conventionally fed, grass fed, or natural-fed. The 5 regions were the High Plains, Southern Plains, Southcentral, Southwest, and Western Plains of the United States. Fecal samples and LN were cultured quantitatively and qualitatively for Salmonella, in addition to screening for antimicrobial susceptibility on isolates. Conventionally-fed and cull dairy cattle had the greatest qualitative prevalence rates in both LN (32% and 18%, respectively) and feces (37% and 49%, respectively), while natural-fed cattle had the lowest prevalence in LN (3%) and feces (7%). Conventionally fed cattle had the greatest Salmonella concentration (1.17 log₁₀ cfu/g) in the LN, while cull dairy had the greatest Salmonella concentration (1.96 log₁₀ cfu/g) in the fecal samples. Seasonal effects differed, but winter consistently presented lowest Salmonella burden. Region 4 (Southwest) presented greater prevalence than other regions for LN and feces. Only 21 Salmonella isolates in this study were identified as MDR, and cull dairy and cull beef cattle were the primary sources (86%). These compelling results suggest that different production schemes may results in varying degrees of hindgut health which could affect ability of Salmonella to reach the LN, though the mechanisms of Salmonella prevalence in LN is far from elucidated. On-farm and in-abattoir Salmonella surveillance remains necessary to better understand production source, seasonal, and regional risks.

Key Words: cattle, lymph nodes, Salmonella.

Presented at the 9th Symposium on Gut Health in Production of Food Animals, St. Louis, USA, 2021. For information on the next edition, click here.