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Researchers surprised by E. coli, water supply study


ITHACA, N.Y. — Water troughs on farms can be a conduit for the spread of E. coli in cattle, according to a major study led by Cornell University College of Veterinary Medicine researchers.

Cows can then spread the pathogen to people through the bacteria in feces. The study was recently published in the journal PLOS ONE. A past study investigated the whole system, everything that is happening with the cows, the bacteria and the environment, said Renata Ivanek, associate professor of epidemiology and the paper’s senior author.

That led to the finding that water troughs might be propagating transmission.

“We were curious about that,” she said. “If water troughs could be used to manage this problem, that would be good because any solution that is simple and not expensive would be our best bet.”

People typically acquire infections from Shiga toxin-producing E. coli through cow feces-contaminated beef and salad greens. The main E. coli strain causes more than 63,000 illnesses a year and about 20 deaths, according to the Centers for Disease Control and Prevention.

Though cows carry and spread E. coli when they defecate, the bacteria do not make them sick. “Farmers do not see a problem because there are no clinical signs in cows,” Ivanek explained. “It is invisible.”

The researchers did a control study with water troughs in a feedlot over two summers. Through modeling, the researchers deemed that propagation of E. coli would be modulated by temperature and the water turnover, Ivanek said. As cows drink from an automatic watering system, the water refills immediately.

“If you leave that level of water at a low level, then the turnover of water will be fast,” she explained. “If you have a large trough, then the turnover will be slower. So our modeling suggested that if weather is really warm, and the turnover is slow, the water will be warmer.

“Warm temperature is an important predictor for bacterial growth. We thought with warmer weather, and a slower water turnover rate, there will be a greater amount of bacteria in the water.”

They tested several pens of cattle that they knew were shedding the E. coli bacteria. The results were surprising – in half of those pens, they reduced the level of water by half, so they refilled faster. They expected that intervention would reduce the prevalence of the bacteria. They made no changes in the other group.

The researchers were startled to learn that the odds of finding E. coli in the cows were about 1.6 times higher in the treatment pens, where the water level was lowered. than in the control pens where they did not change the water level.

“We sampled all 40 cows in each pen,” Ivanek said. “We took fecal samples from each pen before intervention and then three weeks later. We expected that in the group in the pens where we lowered the water level, there would be a reduction in prevalence, but the opposite happened, suggesting that having lower levels of water even makes it worse, as opposed to better.”

Possible explanations are that with more water in the trough, the bacteria concentration is lower, or that with a lower amount of water possibly the cows swallowed more debris. Ivanek said.

The scientists were correct in determining that water troughs can be a conduit in the spread of E. coli, but more research is needed. “The next thing would be to figure out what is the optimal level of water,” she reported.

The work was supported by USDA and done in collaboration among Cornell, Texas A&M University and Texas Tech University.