Mitigation of Salmonella in Cattle Lymph Nodes in a Commercial Feedlot Setting Using NP51, a Lactobacillus-based Pre-harvest Intervention

Introduction: Our laboratory previously conducted a two year surveillance of cattle lymph nodes from multiple regions which indicated that up to 70% were positive for Salmonella during certain seasons of the year.  Salmonella harbored in the lymph nodes of cattle can evade carcass decontamination procedures in slaughter plants.  Some of the lymph nodes including the subiliac are located in the carcass trim utilized for ground beef thereby potentially contaminating the product.

Purpose: This study was conducted to evaluate a pre-harvest direct-fed microbial intervention including Lactobacillus acidophilus NP51 at a rate of 10⁹/head/day (NP51) on the reduction of Salmonella prevalence in cattle lymph nodes.

Methods: Approximately 1,800 cattle were randomized into two treatments in a commercial feedlot with 12 pens/treatment and 75 head/pen.  The treatments included control cattle and cattle supplemented with 10⁹/head/day NP51.  Subiliac lymph nodes were obtained from approximately 25 animals/pen (n= 600) at the slaughter facility and were tested for Salmonella with previously-published qualitative and quantitative methods.

Results: Salmonella was recovered from 25% (P < 0.01) fewer lymph nodes for cattle fed NP51 when compared to controls.  Quantitatively the NP51 cattle had significantly less (P < 0.05) Salmonella in lymph nodes (3.1 vs 4.2 log CFU/lymph node) and per gram of lymph nodes (1.9 vs. 4.2 log CFU/g).  Control samples were more likely to have a higher concentration of Salmonella in lymph nodes with 10.4% vs. 11.7% between 3 and 4 log CFU/g; 13.7% vs. 6.4% between 4 and 5 log CFU/g, and 7.5% vs. 2.1% greater than 5 log CFU/g.

Significance: The results of this study indicate that supplementation with NP51 is an effective pre-harvest intervention to reduce the prevalence of Salmonella in cattle lymph nodes.  This will potentially decrease the contamination of ground beef from lymph nodes and the associated tissues that are incorporated into this product.