Project Summary

Reduction of Pathogens in Fecal and Lymph Node Samples Collected from Beef Cattle Treated with Commercially Available Direct-Fed Microbials

Principle Investigator(s):
Mindy Brashears
International Center for Food Industry Excellence, Department of Animal and Food Sciences, Texas Tech University
Completion Date:
June 2023



  • Data indicates that the direct fed microbials (DFMs) used in this study were effective in reducing fecal shedding of E. coli O157:H7, Salmonella, and C. perfringens and prevalence of Salmonella in PLNs, which means it may be an effective pre-harvest intervention.
  • Pens treated with Probicon, as a pre-harvest intervention, significantly reduced prevalence of E. coli O157:H7 and Salmonella and C. perfringens concentration. 
  • Further research should be conducted on a larger scale in commercial feedlots to determine the efficacy of DFMs, specifically Probicon (L28), on the reduction of foodborne pathogens in fecal shedding and prevalence of Salmonella within bovine PLNs.


Contamination of beef with foodborne pathogens, mainly Salmonella spp. and Escherichia coli O157:H7, poses great risks for public health and creates financial burdens on beef producers if not mitigated properly. Currently, the majority of mitigation measures focus on controlling pathogens at the post-harvest level, using chemical or physical carcass decontamination methods, to ensure regulatory compliance and public health protection. Although implementation of these post-harvest methods has greatly contributed to the advancements of beef product safety, tackling contamination at pre-harvest stages of production can result in lower levels of carcass contamination during processing. The food industry often employs a “multi-hurdle concept” to control microbiological hazards throughout different processing points by using multiple intervention methods, which is known to provide a synergistic effect that increases the efficacy of these interventions, further than if these methods were to be used individually. Similarly, pre-harvest cattle interventions were shown to improve the efficacy of post-harvest interventions and reduce the need for chemical processing aids, that add cost to processors. Direct-fed microbials (DFMs) are live bacterial or fungal cells that can be directly added to animal feed to stabilize the gut microbiome and compete with and inhibit the growth of harmful pathogenic microorganisms, in a similar fashion to probiotic supplements for human use. Therefore, the overall goal of this project was to validate the use of a novel strain of Lactobacillus salivarius L28, as a DFM, to reduce fecal shedding of Salmonella, E. coli O157:H7, Clostridium perfringens, and Enterobacteriaceae and the harborage of Salmonella in the lymph nodes of cattle in commercial feedlot settings, and to compare its effectiveness against cattle without DFM supplementation and cattle fed with an established DFM formulation.


Three different cattle feed yards located in Eastern Nebraska and Western Iowa containing approximately 1000 to 9000 head on feed with 70 to 300 head per pen were selected for this study. Three pens per each feedlot were assigned to either a control group without DFM supplementation, a treatment group with L28 supplemented, and another treatment group with a commercial DFM, Bovamine Defend®, supplemented with the same standard diet. Fecal samples were collected from the floor of each pen at 28 days intervals, over a 5-month period, from May to September 2021 and analyzed for the presence and/or levels of Salmonella, E. coli O157:H7, Clostridium perfringens, and Enterobacteriaceae by an independent laboratory using state of the art technologies for microbial detection and enumeration. Subiliac peripheral lymph nodes were also collected over a two-month period, from the carcasses of the same cattle used in fecal sampling, during slaughter and were analyzed by the Food Microbiology Laboratory at Texas Tech University.

Overall, results indicated that L28 had greater or similar effect on reducing the prevalence of E. coli O157:H7 and Salmonella, and concentration of C. perfringens when compared to another commercial DFM product. Our results are in accordance with the previously published reports on the effectiveness of DFMs to control E. coli O157:H7 and Salmonella for improved food safety. Results also indicate that L28 can reduce pathogen prevalence with lower doses of the supplemented DFM. Studies on the effect of DFMs to control C. perfringens are scarce, although this species is a clinically important human and animal pathogen, but these results indicate that L28 is effective in reducing the concentration, compared to other commercial DFMs, even at lower doses of supplementation. The results also indicate that DFMs used in this study are effective in reducing prevalence in lymph nodes and has the potential to mitigate the risk of salmonellosis due to consumption of ground beef, costly recalls, rejected products, and reprocessing for the beef industry.

Cattle lymph nodes are an important source of Salmonella contamination in ground beef, as this pathogen can chronically infect the lymph nodes and often end up in trimmings to be grinded. Removal of lymph nodes during post-harvest is time consuming and requires skilled workers; therefore, it is not feasible to control lymph node contamination by post-harvest removal. Instead, pre-harvest interventions such as the DFMs reported in this study, are essential to controlling Salmonella contamination in ground beef. It is expected that the results obtained from this study will help to improve food safety, human health, and animal welfare throughout the beef supply chain, by the implementation of the novel L. salivarius L28 strain in pre-harvest cattle operations, and provide incentive for further research in commercial settings and possible extension to other livestock like poultry and swine operations.