Last week the Ohio State University Extension did a story on how sawdust bedding farmers use for their cows to keep costs down might have a hidden price tag: human health.
Research done by Ohio State University veterinary scientist Jeff LeJeune suggests there is a direct link between this cheap livestock bedding and E. coli 0157:H7.
LeJune tested cattle for E. coli O157:H7 during the summer and early fall of 2003 on farms that spread either sand or sawdust in stalls. A total of 3,600 fecal samples from 20 northeast Ohio commercial farms – 10 using sand and 10 using sawdust – were gathered and analyzed. Each farm was visited six times at two-week intervals to collect samples.
Results showed the prevalence of E. coli O157:H7 in animals from sand-bedded herds (1.4%) is significantly lower than in animals from sawdust-bedded herds (3.1%). The total number of positive samples in sand-bedded animals (25 out of 1,800) was less than half that found in sawdust-bedded animals (56 out 1,800).
“The choice of bedding has an unseen but real food safety risk,” LeJeune says. “Bedding is one of the first factors affecting incidence of E. coli O157:H7 in dairy cows, as far as management practices, that has been proven through research.”
Cattle manure is considered the primary source of E. coli O157:H7 contamination in foods and the environment. Higher counts of this pathogen on dairy farms are a concern, LeJeune says, because of the increased risk of contamination to the environment, farm workers, farmhouses and people who drink unpasteurized milk. But the risk extends far beyond the farm.
“Approximately 17% of ground beef comes from dairy cows that go to slaughter,” LeJeune says. “One cow contaminated with E. coli O157:H7 that has been sent to the slaughterhouse can contaminate many other cows, and this can result in the contamination of millions of pounds of ground beef. One cow can excrete about one million E. coli organisms in each gram of feces. And it only takes less than 1,000 of those bacteria to make a person sick.”
Why does sand beat sawdust?
Why cows on sand harbor less E. coli O157:H7 than those on sawdust is a complex question, LeJeune says. Under laboratory conditions, sawdust bedding not only yielded higher counts of E. coli O157:H7 than sand bedding, but it also harbored the pathogen longer. This was confirmed by on-farm sampling.
The number of days when feces tested positive for E. coli O157:H7 was higher in sawdust-bedded herds (22 out of 60 days) as compared to sand-bedded herds (13 out of 60 days).
One explanation may be that sand bedding contains less available organic matter and nutrients than sawdust. That means bacteria can’t reproduce as easily . Sand also has lower water content, which is believed to inhibit bacterial growth in fresh bedding.
But, there’s another possible explanation:
Bacterial contaminants present in bedding can be liberated into the air when handled, distributed or removed from the barn, LeJeune says. Airborne particles of dust are usually trapped in the upper airway and then swallowed. In addition, E. coli O157:H7 carried on dust particles may contaminate feed, water sources or the animals’ hide.
The results of the study were published in the January 2005 issue of Applied and Environmental Microbiology.