According to research led by USDA scientist Terry Arthur, on average, about 2% of the cattle in pastures or pens may be "supershedders" – animals that shed high levels of pathogenic organisms such as E. coli O157:H7 in their manure.
Scientists are turning their attention to supershedding, because it could increase the amount of E. coli O157:H7 that makes its way from pasture or feedlot pen into packinghouses, later making people sick if the resulting meat is not cooked properly.
Arthur, along with colleagues at the USDA Agricultural Research Service Meat Animal Research Center in Clay Center, Neb., are finding a strong basis for new and effective strategies to curb shedding of this bacterium.
Conducting studies of 6,000 head of feedlot cattle and more than 13,000 manure, hide and carcass samples, the team found that O157 colonization in supershedder cattle may occur not just in the lower digestive tract, but also throughout the animals' entire digestive system. This information may help packinghouse managers better evaluate their facility's sanitation procedures.
The researchers were also the first to determine that supershedding was not restricted to any particular O157 strain. Their work rules out the idea that tactics designed to reduce supershedding should target a specific strain or strains.
Research by the group also determined that in order for a cattle-management strategy to be deemed successful for reducing transmission of O157, no more than 20% of the cattle targeted by the intervention would be shedding the microbe at any one time, and none would be shedding it at supershedder quantities.
More E. coli work
In related work at USMARC, researchers Jim Bono and Jim Wells, along with colleague Andy Benson of the University of Nebraska-Lincoln and others, are working to determine why some cattle are supershedders while others are not.
In one set of studies, these scientists are inventorying and comparing the microbes that live in the gastrointestinal tract of supershedders with those dwelling in non-supershedders. This work may provide clues about whether some microbial species and strains help O157 flourish or, conversely, whether some “beneficial” species outcompete and suppress it.
Such data may be useful in developing approaches to help the beneficial strains proliferate in cattle.
In another line of inquiry, geneticists Larry Kuehn and Warren Snelling are scrutinizing the genetic makeup of supershedders to determine whether supershedding is a gene-controlled trait. If it is, it may be possible to breed the trait out of tomorrow’s beef cattle, USDA said.
A full overview of the research is discussed in the latest issue of Agricultural Research magazine.