Project Summary

Reduction of E. coli O157:H7 in Beef Feedlot Cattle Using Varying Doses of a Direct-Fed Microbial (DFM)

Principle Investigator(s):
Mindy Brashears, Ph.D.
Texas Tech University
Completion Date:
April 2004



E. coli contamination on beef cattle hides continues to be a major beef safety issue for the industry. Reducing pathogen loads as they come into the harvest facility is one step in a multiple step intervention process. Intervention methods in place within the facility will be enhanced if pathogen loads are mitigated before the cattle enter the harvest facility.

The overall objective of this study was to evaluate the effects of three different doses of NP51 and the combination of NP51 and NP45 fed to finishing beef cattle on the prevalence of E. coli in the feces and on the hides. 


Three hundred steers were received, and individual body weights were used to sort the steers into twelve blocks. Within each weight block, steers were randomly assigned to one of five treatments and penned (five animals/pen). There was a total of twelve pens assigned to each of the five treatments (five pens/block). All cattle received a standard steam-flaked corn-based finishing diet (92% concentrate) throughout the feeding period.

The five treatments included four Direct Fed Microbial (DFM) treatments and a control (no added DFM) as follows:

  1. Control - no added DFM
  2. HNP51 - high dose of NP51 at 1 x 109 CFU/steer daily
  3. MNP51 - mid-level dose of NP51 at 1 x 108 CFU/steer daily
  4. LNP51 - low dose of NP51 at 1 x 107 CFU/steer daily
  5. NP51+45 - NP51 at 1 x 109 CFU/steer daily and NP45 at 1 x 109 CFU/steer daily 

All four treatments containing NP51 also contained Propionibacterium freudenreichii at 1 x 109 CFU per steer daily.

Fecal and hide samples were collected from all cattle to determine the baseline prevalence of E. coli O157. Fecal samples were collected from each animal on the first day of the feeding period, and every subsequent 28 days until cattle were marketed for harvest. Cattle were marketed in blocks according to when the majority of cattle within a block(s) had reached a body weight and composition desired to achieve a USDA quality grade of Choice. On the day of harvest, both individual fecal and hide samples were collected from the live animal at the feedlot. All samples were analyzed and compared for E. coli O157.


Fecal Prevalence. The overall prevalence of cattle shedding E. coli O157 at the initiation of the trial was 14.7% (44 of 300 fecal samples collected). There were no statistically significant differences (P<0.20) in the prevalence of fecal shedding across treatment groups. Two animals were removed from the study before the collection of samples on day 28 for reasons unrelated to the treatments.

Overall, cattle receiving HNP51, MNP51, and LNP51 had a lower (P < 0.01) prevalence of E. coli O157 fecal shedding throughout the feeding period compared with cattle receiving the control diet. Cattle receiving HNP51 or LNP51 were significantly less likely to be shedding E. coli O157 at harvest than the controls (P < 0.01 and P = 0.03, respectively). Cattle receiving MNP51 were marginally (P = 0.12) less likely to be shedding at harvest compared to the controls. There was no significant difference in fecal prevalence at harvest for the NP51+45 group versus controls. Hide Prevalence. Cattle receiving HNP51 were 62% less likely to be carrying E. coli O157 on their hides than the controls; however, this estimate was only marginally significant (P = 0.12). Hide prevalence of E. coli O157 among those receiving LNP52, MNP51, and NP51+45 was not different (P = 0.46, 0.25, and 0.99, respectively) from those receiving the control diet. Overall Prevalence. Cattle receiving HNP51, MNP51, and LNP51 were 81, 65, and 72% less likely to be classified as “positive” at harvest than the controls (P = 0.01, 0.03, and 0.01, respectively). The proportion of cattle receiving NP51+45 classified as “positive” was not different than the controls (P = 0.73).


Previously, the findings of two past studies conducted at Texas Tech University indicated that cattle receiving a 1 x 109 CFU/steer daily dose of NP51 were approximately 50% less likely to be shedding E. coli O157 compared to animals receiving no DFM. Likewise, in the current study, cattle receiving a diet supplemented with the high-level dose of NP51 had the lowest prevalence of shedding E. coli O157. However, the findings of this study indicate that feeding lower doses of NP51 may also be effective in decreasing the prevalence of fecal shedding of E. coli O157 during the feeding period. The higher prevalence of E. coli O157 shedding observed among cattle receiving NP51 plus NP45 compared to those cattle receiving only NP51 may indicate that the two organisms are antagonistic. This finding was also observed in a previous study in which decreased efficiency was detected in cattle receiving both of these organisms. There were no detrimental effects of the DFM treatments used in these studies on animal performance.

Table 1. Shedding and Prevalence of E. coli O157 by Treatment.







Fecal Shedding 1+ Times






Average Number Fecal Shedding Times Among Positive Cattle






Fecal Prevalence at Harvest






Hide Prevalence at Harvest






Overall Prevalence at Harvest*






* “Overall Prevalence at Harvest” includes cattle that were positive for E. coli O157 in the feces and/or on the hide.