Feeds can affect E. Coli levels in cattle manure
by Heather Smith Thomas
Several types of E. coli are normal residents in bovine digestive tracts. Some cause illness in baby calves and some (such as E.coli 0157:H7) can cause illness in humans if meat is contaminated by manure on hides at slaughter. Studies have shown that levels of E. coli in the gut (and subsequent risk for contamination) are influenced by feed.
Earlier studies showed that cattle fed finishing diets that include wet distillers grains with solubles (WDGS) have higher percentages of animals with E. coli 0157:H7 in feces and on their hides. Studies at USDA’s Meat Animal Rsearch Center, Clay Center, Nebraska, led by Dr. James Wells, Research Microbiologist, looked into how E. coli levels could be reduced by altering feed during the finishing phase. Feeding trials compared effects of feeding different levels of WDGS.
“When we fed diets with high levels (40%), it prolonged survival of that pathogen in feces,” says Wells. A larger study, published in 2009, involved 605 steers dividedi nto 2 groups. One group received no distiller’s grain. The other group was fed 40% WDGS in the finishing ration. Levels of E.coli 0157:H7 were monitored in feces, in manure on the ground, and on hide samples. A wet sponge is run over the hide to pick up a sample.
The animals were monitored in the growing phase (fed 14% WDGSon a dry matter basis), and only a slight increase in prevalence of E. coli 0157:H7 was found in those fecal samples.
“After the growing phase we put one group on a finishing ration (40% WDGS on a dry matter basis), and the other group on 0%. Our control diet was dry-rolled and high-moisture corn,” says Wells.
Throughout the finishing phase, animals were sampled every 4 weeks. “We had more fecal positives—higher percent of animals with countable levels in feces—when we fed 40% WDGS, as well as higher prevalence in feces,” he says.
“Diet made a difference in the fecal environment, influencing survival of bacteria. We also saw increases in generic E. coli—the normal types always found in the gut. The E. coli 0157:H7 is also there, but usually in very low numbers. We found that some cattle are super-shedders of E. coli 0157:H7 but even the super-shedders are putting out much lower numbers than generic species. The E.coli 0157:H7 are only a very small fraction of the total E. coli in the gut.”
In addition to difference in feces (in animals fed WDGS), the researchers also saw more animals with countable levels in hide samples.“Harvesting plants are addressing this problem with hide washers. From data collected here in the Meat Safety and Quality Research Unit, this seems to be effective in reducing carcass contamination. But its an extra step that involves water, energy and space during slaughter,” says Wells.
To reduce numbers of E. coli0157:H7 in the feedlot environment, we need to reduce the number of animals with countable levels in feces. However, we still don’t know what makes a certain animal become a super-shedder.
“Researchers are looking to see if there is some host factor; maybe that animal is unable to keep those bacteria at low numbers. We’re also checking for anything different in that bacterial micro-biome (complex of bacteria in the gut). Other bacteria in that colon environment may be altering the balance, ”says Wells.
Another study, published in 2011, looked at whether the amount of WDGS could be reduced in finishing rations—replaced with dry rolled corn—prior to harvest,to see how long it might take for bacterial levels to drop. A 2-yearstudy (300 animals each year) were fed either 0, 40 or 70% WDGS on a dry matter basis through the first part of the finishing phase.
“At 56 days prior to harvest we reduced the WDGS to either zero or 15% in most of the cattle, but maintained some at 40%. When we reduced WDGS down to zero or 15% prior to harvest, by day 28 we saw differences in hide samples for countable levels and prevalence for E. coli 0157:H7, and by day 56, countable levels and prevalence were comparable to animals fed corn continuously. Al lwere significantly lower than in animals fed 40% through the whole study,” says Wells.
Thus feed management could be an option for feedlots trying to reduce incidence of hide contamination with E. coli 0157:H7. “With the price of corn, this might not be economical for all producers—to feed more corn and less WDGS. So we’re trying to determine whether there are factors in the WDGS (in addition to micro-biome and host factors) that might alter levels of E.coli 0157:H7 in laboratory studies. If successful, we could follow with feedlot studies and see if there ar eways we could reduce or change that component in WDGS to eliminate the problem,” he explains.
“The beef industry has invested billions of dollars in interventions at harvest and has done a good job reducing the problem of E. coli0157:H7. Our goal is to discover what is going on in the pre-harvest environment—to have better control of E. coli 0157:H7 during that time, and learn how we might implement pre-harvest intervention if need be,” says Wells.