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E. coli persistence points to importance of feedlot waste management

The strong persistence of E. coli and other bacteria in cattle manure and liquid effluent illustrates the importance of proper management to reduce the risk of environmental contamination from cattle feedlots, concludes a study by Agriculture and Agri-Food Canada (AAFC) researchers.

E. coli and other bacteria can survive in manure and catch basin effluent for up to several months, says Dr. Jim Miller, a research scientist at AAFC's Lethbridge Research Centre, specializing in soil and water quality issues. Miller examined the persistence of bacteria and nutrients in feedlot manure as part of a broad three-year project that investigated the links between feedlot manure, water quality and human health. This project was supported in part by the Canada/Alberta Beef Industry Development Fund (CABIDF.)

"The bottom line is manure and liquid effluent need to be managed properly," says Miller. "In different components of our study, we found that E. coli and other types of bacteria can survive anywhere from several days to several months in manure and effluent, so proper management is essential to ensure these bacteria are not transferred to the environment."

The study also uncovered significant variations in manure nutrient levels at different times throughout the year. Amounts of manure phosphorus and nitrogen varied from month to month, at levels significant enough to consider when spreading manure on land. "This shows the importance of nutrient testing to help match manure application rates to soil and crop requirements," says Miller.

Other components of the broad CABIDF-supported project investigated a range of questions related to the transport of manure bacteria and nutrients. While some of these components are still undergoing data analysis and peer review, there are several other results ready to be reported, says Miller.

In a study of bacteria persistence in feedlot bedding material, researchers found no difference between straw or woodchip bedding on E. coli and total coliform counts. Miller had thought the chemical composition of woodchips might reduce E. coli populations, but this wasn't the case. With both types of bedding material, the study found E. coli counts were higher in summer than in cooler seasons.

In another project component, researchers concluded that standard design specifications used to size catch basins for effluent runoff are adequate. Existing criteria requires catch basins to be large enough to handle a 1-in-30 year extreme rainfall event.

Researchers also examined the chemistry composition of effluent collected in catch basins. They concluded that effluent - like manure - is high in potassium and other nutrients, and should be treated as a fertilizer source.

As part of this component, they also found that E. coli bacteria persist in catch basin effluent throughout the year, at varying levels. E. coli was present the soil at the bottom of catch basins and researchers observed that it remains in the soil even as catch basins empty or dry out. Based on this, they concluded water entering catch basins carries a high risk of contamination by E. coli. Miller suggests basins need to be lined with an impermeable material, such as clay, to prevent E. coli from leaching into groundwater.

In a related component, researchers found that E. coli bacteria survive in barley crops and in soil when catch basin effluent is used for irrigation. Pathogen survival period ranged from several days to several weeks. "For producers using effluent for irrigation, the message is to leave sufficient time between the last irrigation and harvest of the forage crop to avoid E. coli contamination in feed," says Miller.

In applying higher rates of raw manure to crops, researchers found E. coli can persist in the soil throughout the entire year. The project involved manure application rates in the 70 to 80 tonnes/hectare range, which are high but not uncommon.

"Field selection is important to minimize the risk of off-site transport of the pathogen," says Miller. "Manure should not be applied to sloped fields where there's risk of run off and it should be avoided on sandy soils where there is potential for E. coli to leach into ground water.

"While the soil is a good filter, these bacteria do persist," he says. "Provided they don't move off the site, they will degrade and pose no environmental concern."

CABIDF is a joint $16.4 million fund of Alberta Agriculture, Food and Rural Development and Agriculture and Agri-Food Canada. The Fund is administered by Alberta Beef Producers and has supported more than 50 projects in five major categories identified to benefit the Alberta beef industry.

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