Data from a small study on cattle that expel large amounts of E. coli bacteria in their manure shows surprising results, says one of the re-searchers involved.
Tim McAllister, an Agriculture Canada researcher and expert on cattle nutrition and microbial ecology, said super shedders, as these cattle are known, may not be as big a factor in the spread of E. coli as has previously been thought.
The massive recall of beef from the XL Foods plant in Brooks, Alta., was prompted by discovery of E. coli 0157:H7 in some products. Early speculation about bacterial source suggested it arrived on manure from a “high event day” when the plant processed several super shedder cattle.
“In reality, I don’t really think we have the scientific data to draw that linkage,” McAllister said at an Oct. 25 meeting of the Southern Alberta Council on Public Affairs.
It has been proposed in science circles that five percent of the cattle population reach super shedder status, and those few are responsible for 80 to 90 percent of E. coli transmission in feedlots.
McAllister and his colleagues studies 400 cattle from one feedlot. By testing manure samples, they identified 13 to 16 super shedders, which had more than 10,000 E. coli cells per gram of manure. The norm is 10 to 100 cells per gram.
The research centre bought the super shedders and moved them to its own facilities. Only two of the group were still super shedders after the four days that were required to move the cattle.
Further tests showed some cattle were super shedders in the morning but normal by afternoon.
Stressors imposed on the cattle, including longer transport, chute handling and diet changes, did not seem to encourage super shedders, said McAllister.
“So are those super shedders responsible for high event days? Maybe not,” he said.
“If transporting them causes them to stop being super shedders, then they wouldn’t be as big an issue. We really don’t know the answer.”
McAllister cautioned that the study was small and more work must be done on the subject. Grant applications have been made.
“It almost implies that the E. coli are in the digestive tract and they are sporadically released,” he said.
“So there’s something in the animal that triggers the release and then (bacteria) build back up and then they are triggered to release again.”
Complicating matters is the fact that there is more than one strain of E. coli 0157:H7, and some are less harmful to humans than the strain now at issue with the recall.
Vaccines are available that will lower E. coli in bovine digestive tracts, but McAllister said they will not eliminate the bacteria.