Effect of Direct-fed Microbial Supplementation on the Presence of Salmonella enterica in Bovine Peripheral Lymph Nodes

Introduction: Bovine peripheral lymph nodes (LN) contained within adipose trim, have been identified as a potential source of human exposure to Salmonella enterica, when incorporated into ground beef. How Salmonella gain entry to peripheral LN is a question yet to be answered, however recent survey data indicate that Salmonella prevalence and levels in feedlot environments may play a significant role. Thus there is a perceived need to identify pre-harvest measures for preventing Salmonella entry into this niche.

Purpose: To determine the effect of feeding a direct-fed microbial, Bovamine^®†, on Salmonella prevalence and levels in bovine peripheral LN.

Methods: Cattle (n = 3,259) were housed in a commercial feed yard setting and divided among 24 pens (avg. 135 hd/pen), such that there were 12 treated and control paired pen replicates. Treated cattle were fed a standard ration with the addition of Bovamine^® (~10⁷CFU/hd/d), while control cattle were fed the standard ration. Cattle within each pen pair were harvested at the same processing plant, on the same day. At harvest, one subiliac LN was removed from 30 randomly selected carcasses per pen, for a total of 720 LN collected. All samples were analyzed for Salmonella prevalence and level. 

Results: Average Salmonella prevalence for all LN tested was 41.9%, with treated found to be significantly lower than control cattle (35% vs. 48.7%; P = 0.0189). Salmonella contamination levels were generally low with the majority of LN (71.1%) containing between 0 to 20 CFU/LN. While 10.6% of LN overall were found highly contaminated (≥4.0 log CFU/LN), the percentage of treated were lower than control in this category (6.1% vs. 15%, respectively), although not significantly (P = 0.1697). 

Significance: These data suggest that direct-fed microbials may be a beneficial component of a multi-hurdle, pre-harvest approach, aimed at decreasing Salmonella contamination of bovine peripheral lymph nodes. 

^†Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.