In 2010, 150,000 pounds of meat were recalled as a result of possible contamination with Escherichia coli O157:H7. It is estimated that the annual cost of E. coli O157:H7 on the food industry in the United States is $405 million.
Escherichia coli O157:H7 causes serious gastrointestinal infections and can be transmitted among other means, by ground beef and fresh vegetables.
The first recognized human illness for E. coli O157:H7 was in 1982 from contaminated hamburger. Seventy-three thousand illnesses are reported annually in the United States with a spike in the summertime as more families are enjoying outdoor activities such as home grilling, fresh vegetables from the garden and more frequent contact with domestic animals.
Cattle shed this bacterium in their feces, but its excretion usually follows a seasonal pattern with the largest prevalence in the summer months.
The beef processing industry has implemented many intervention strategies in harvest facilities, such as antimicrobials and hides washes. Recently, interest has increased in pre-harvest strategies, such as feeding a probiotic, vaccinations, and bacteriophage treatments in hopes of reducing the percentage of E. coli entering the harvest facility as well as the pathogen load in the gastrointestinal tract of cattle.
As the ethanol industry grew it was suggested that feeding distillers grains, a byproduct of ethanol processing, caused an increase in the prevalence of E. coli O157:H7 in cattle. Researchers suggested that distillers grains may contain components that directly or indirectly stimulate growth of E. coli O157:H7. Because distillers grains partially replace corn or a cereal grain in the diet, there is a reduction in dietary starch and increased flow of non-starch fractions, as lipid and protein, into the hindgut. This may favor the growth and persistence of E. coli O157:H7 by altering the microbial ecosystem.
Previous research has shown inconsistent results regarding an increase in E.coli O157:H7 prevalence attributed to feeding distillers grains to cattle. In 2009, researchers at Kansas State University reported no significant effects of dried distillers grains with solubles, or dry rolled corn, on E. coli O157:H7 prevalence in cattle.
In 2008, researchers at Kansas State conducted three studies related to this topic. One reported that on day 122 cattle were more likely to shed E. coli O157:H7 when fed 25 percent distillers grains in the diet, but on day 136 there was no effect of feeding distillers grains on the shedding prevalence of E. coli O157:H7.
A second study found that distillers grains significantly increased E. coli O157:H7 shedding, in samples collected off the pen floor. A third found an overall low prevalence of 5 percent and that distillers grains had no significant effect on the prevalence of E. coli O157:H7.
In 2007, researchers at the University of Nebraska found a significant effect on the level of distillers grains on the shedding of E. coli O157:H7.
Researchers at the University of Minnesota are currently conducting a two year study to evaluate the prevalence of E. coli O157:H7 in Minnesota cattle fed distillers grains in the feedlot and upon entering an abattoir.
For year one, three farms sites were evaluated, comprising of a one-time capacity of approximately 8,000 cattle. The feedlots evaluated represented a wide variety of facility types (open, enclosed, and slatted floor) and cattle types (calves and yearlings).
Multiple pens of cattle within each site were sampled. Fresh fecal samples (n=1,457) were collected randomly from the feedlot floor at 5 percent of the pen population at least once a month for a year.
Results indicate an overall E. coli O157:H7 prevalence of 9.06 percent when averaged across the three farm sites. Prevalence within the three sites measured 4.18, 11.22, and 9.42 percent. No difference has been observed for the probability of E. coli O157:H7 in cattle fed high (greater than 25.5 percent) and low (less than 25 percent) dietary inclusion of distillers grains.
Researchers have observed the highest prevalence for shedding of E. coli O157:H7 in the summer (30.71 percent) and the lowest prevalence in November (1.90 percent). At the abattoir, fresh fecal samples (n=1,201) were collected randomly once a month. The total population samples consisted of 4,166 head of cattle and 59 lots.
The overall E. coli O157:H7 prevalence was 11.66 percent when averaged across all samples. Researchers have noted that of the positive results, the highest prevalence for shedding of E. coli O157:H7 in the winter months (76 percent) and the lowest prevalence in the summer (5 percent).
The probability of E. coli O157:H7 found in cattle fed distillers grains was lower than cattle not fed distillers grains. Dietary inclusion level of distillers grains has not affected E. coli O157:H7 prevalence in Minnesota-fed feedlot cattle in research completed thus far, however this data collection will continue another year.
The shedding of E. coli O157:H7 in cattle greatly fluctuates. It is important that proper intervention to control and minimize the spread of E. coli from cattle to food products and the environment is practiced at all times of the year.