Background 

Past research has demonstrated that cattle are a major reservoir for E. coli O157:H7 and that this pathogen is shed through their feces. Various factors may impact the fecal prevalence of E. coli O157:H7 in cattle, including their diet. Previous studies have demonstrated that forage-fed cattle persistently shed E. coli O157:H7 longer than cattle on a primarily corn-based ration. Cereal grains, such as corn, are rich in starch, which can be digested and fermented to yield ethanol. The residual product that is present after ethanol distillation is known as wet distillers grain (WDG). This byproduct is dense in energy and protein and has become a common component in cattle feedlot rations due to its availability as a byproduct of the ethanol industry. Significant levels of distillers grains in cattle rations may have the potential to change gastrointestinal ecology and may alter E. coli O157:H7 prevalence in feces.   Previous research has demonstrated up to a 2.5-fold increase in feedlot pen fecal prevalence for E. coli O157:H7 when 25 percent dried distillers grain was included in a ration. Other existing studies however, have shown conflicting results on the effect of wet distillers grains on E. coli O157:H7 in cattle.   

The objective of this research was to determine the effect of the level of wet distiller’s grain in a feedlot ration (zero versus 40 percent on a dry-matter basis) on the prevalence and level of E. coli O157:H7 in cattle feces and on cattle hides.

Methodology 

A total of 603 steers were identified and randomly assigned to one of two dietary treatment groups—with and without wet distillers grains. In the experimental group that was fed wet distillers grains with solubles (WDGS) during the growing phase, the WDGS replaced corn to yield a diet with 13.9 percent WDGS on a dry matter basis. The steers were transitioned from a growing ration to a finishing ration with three intermediate formulations. The growth phase of the study ended on day 77 and the finishing period concluded on day 217. The final finishing ration included either 0 percent WDGS for the control group (n = 302) or 40 percent WDGS (n = 301) for the experimental group. At the conclusion of the study, there were 596 animals still on study.   

Fecal samples and hide swabs were collected from each steer on days zero, 28, 49, 77, 105, 133, 161, 189 and 217. These samples were analyzed for prevalence and were enumerated for E. coli O157:H7.

Findings 

In this study, feeding wet distillers grains with solubles in the growing ration was associated with higher hide and fecal prevalence for E. coli O157:H7 when compared to animals without WDGS. The WDGS pens of cattle averaged 5.26 ± 2.03 for hide enumeration for E. coli O157:H7. This result was not statistically different than the results from the control group. However, the percent hide prevalence for E. coli O157:H7 was greater for WDGS fed cattle versus those cattle receiving the control ration. Overall, the E. coli O157:H7 levels were low for both the experimental and control groups.   

The researchers noted that the percent of positive E. coli O157:H7 positive samples was lowest during one month of the study (February 2008), which adds support to previous work that demonstrated seasonality plays a role in pathogen shedding rates. Additionally, the entire spring was characterized by cooler than normal temperatures, which may have contributed to the lower levels of E. coli O157:H7 observed during the finishing phase of this study. In general, during the finishing phase, the animals that received 40 percent WDGS (on a dry matter basis) in their diet had slightly greater prevalence of E. coli O157:H7 on hides and in feces, however the feces difference was primarily attributable to one pen.

Implications   

Due to the seasonality effects observed during the finishing phase of this experiment, the investigator concluded that more research should be done. Additional studies with feedlot animals during the summer months would be useful to determine if high levels of WDGS in the finishing ration affects pathogen loads when E. coli O157:H7 prevalence is highest.