Deciphering the Puzzle of ‘Supershedder’ Cattle

In every herd of 100 cattle, odds are you’ll find about two that are “supershedders”—cattle who shed high levels of pathogens like E. coli 0157:H7 in their manure, potentially spreading it to the rest of the herd and raising the risk of contaminating meat products down the line.

A team of scientists at the USDA’s Roman L. Hruska U.S. Meat Animal Research Center in Clay Center, Neb., has spent the past several years building up a body of knowledge about supershedders, based on studies of some 6,000 head of feedlot cattle and more than 13,000 manure, hide, and carcass samples. To date, they have determined that:

• About 2 percent of cattle on average are supershedders;
• Supershedders are responsible for the majority of E. coli contamination in feedlot pens;
• E. coli colonization in supershedder cattle is found throughout the digestive system, not just in the lower digestive tract; and
• Supershedders may be colonized with any of a variety of E. coli strains, no single strain has dominated in the mixture of samples studied by the USDA team.

That most recent finding, which appeared in the Journal of Applied & Environmental Microbiology last year, has helped to direct the researchers’ current work.

“The mitigation strategy for controlling supershedding will not be able to be designed for certain strains,” says Terrence Arthur, PhD, a USDA Agricultural Research Service microbiologist and one of the lead investigators on the project. “So other members of our group are now examining other factors. If it isn’t the strain, is it something with the host? Is it something about the cattle—perhaps something genetic, or something in the microbiome of the particular animals that allows them to become supershedders?”

Dr. Arthur’s team has also established tentative criteria for the success of interventions aimed at mitigating supershedding: None of the cattle in the pasture or pen are supershedders, and less than 20 percent of the cattle in the pen are low-level shedders. “Right now, it’s difficult to say what’s ‘normal’ in terms of the number of cattle in a pen that shed O157. We’ve seen anywhere from 0 to 100 percent, and we’re trying to define factors that are responsible for the differences,” Dr. Arthur says.