The Use of Direct‐Fed Microbials to Reduce Shedding of Escherichia coli O157 in Beef Cattle: A Systematic Review and Meta‐analysis

Summary Human illness due to infections with Escherichia coli O 157 is a serious health concern. Infection occurs through direct contact with infected animals or their faeces, through contaminated food or water and/or through person‐to‐person transmission. A reduction in faecal E. coli O 157 shedding in cattle might reduce the burden of human infections. We used systematic review and meta‐analysis to assess the efficacy of direct‐fed microbials ( DFM ), compared with placebo or no treatment, fed during the pre‐harvest stage of production in reducing faecal E. coli O 157 shedding in beef cattle during field trials. Four electronic databases, Nebraska Beef Reports and review article reference lists were searched. A total of 16 publications assessing faecal shedding at the end of the trial and/or throughout the trial period were included. The majority of publicly disseminated trials evaluated the prevalence of E. coli O 157 faecal shedding; only two evaluated the concentration of organisms in faeces. The prevalence of faecal E. coli O 157 shedding in cattle is significantly reduced by DFM treatments (summary effect size for all DFM – OR  = 0.46; CI  = 0.36–0.60). The DFM combination Lactobacillus acidophilus ( NP 51) and Propionibacterium freudenreichii ( NP 24) was more efficacious in reducing the prevalence of faecal E. coli O157 shedding at the time of harvest and throughout the trial period compared with the group of other DFM , although this difference was not statistically significant. Furthermore, we found that the combination [ NP 51 and NP 24] treatment was more efficacious in reducing the prevalence of faecal E. coli O 157 shedding at the time of harvest and throughout the trial period when fed at the dose of 10 9   CFU /animal/day than any lesser amount, although this difference was not statistically significant. Feeding beef cattle DFM during the pre‐harvest stage of production reduces the prevalence of E. coli O 157 faecal shedding and might effectively reduce human infections.