218 Evaluation of a Direct-Fed Microbial Product (DIRECTä) on Fecal Shedding of Shiga Toxin-Producing Escherichia Coli in Finishing Cattle in a Commercial Feedlot

Abstract

Abstract Shiga toxin-producing Escherichia coli (STEC), particularly seven serogroups O26, O45, O103, O111, O121, O145, and O157, are major food borne pathogens. Cattle are a major reservoir in which STEC colonize the hindgut and are shed in the feces. Most cattle shed the organisms at low concentrations and a small proportion, called super shedders, shed at high concentrations (≥ 104 per g). Our objective was to evaluate the effect of a commercial DFM product containing lactic acid and propionic acid bacteria (Microbios Direct LA = 1 x 107 CFU and Direct PRO = 5 x 107 CFU/animal/d). The study was conducted in a commercial feedlot and a total of 16 pens were randomly assigned to control or DFM-treated group. Twenty pen-floor fecal samples were collected from each pen on 3 occasions, at 2-week intervals, approximately 100 d after DFM supplementation. Fecal samples were subjected to culture and PCR methods to quantify E. coli O157 and determine prevalence of the 6 non-O157 serogroups and 4 major virulence genes, Shiga toxins 1 and 2, intimin (an adhesin) and enterohemolysin. Data were analyzed using PROC MIXED procedure with pen as the experimental unit. The treatment means comparison within sampling day were carried out for variables that showed significant treatment and sampling day interaction. The overall fecal shedding of E. coli O157 was higher in the control group than in the DFM group, and the difference was significant in the third sampling day. Among the top-6 STEC, O26 and O103 were the dominant serogroups. The prevalence of the 4 major STEC virulence genes and the non-O157 STEC serogroups were not affected by inclusion of the DFM in the diet. In conclusion, DFM supplementation appeared to reduce fecal shedding E. coli O157, but prevalence of the 6 non-O157 serogroups and virulence genes were not affected.