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How many of you use cow manure to fertilize your farms? It’s low-cost, and there’s plenty of cattle manure around. There is, however, one risk to using it as fertilizer: It can contain antimicrobial resistant bacteria.
While some bacteria is good, others are not (think salmonella, yesinia and E. coli). Exposure to those bacteria could have adverse side effects, including nausea, vomiting, fever, diarrhea (and at times bloody diarrhea) and more. A research team in Alberta, Canada, led by Tim McAllister, Ruminant Microbiology and Nutrition Principal Research Scientist at the Lethbridge Research Centre of Agriculture and Agri-Food Canada, studied ways to target antimicrobial resistant bacteria in cattle manure, American Society of Agronomy reports.
“The trick is finding which [bacteria] become resistant and whether or not those will affect human health,” McAllister told American Society of Agronomy. “When you use antibiotics [to keep cattle healthy], bacterial resistance is inevitable. There’s always tradeoffs in nature. It really is a matter of which bacteria become resistant and if it has any implications for human health.”
The feces and urine of cattle that have been fed or injected antibiotics may contain residues of them.
According to American Society of Agronomy, McAllister said, “Even the most pristine soils harbor antibiotic resistant bacteria. Then it’s a matter of figuring out if these resistant bacteria exchange DNA with other bacteria that could cause human infections. It’s a remote possibility considering that most bacteria that survive well in the human body do less well in the broader environment.”
Because high temperatures can kill most bacteria, farmers often “cook” the manure before using it as fertilizer. The two ways to do this is through stockpiling and Windrow composting. Stockpiling involves forming dense piles of manure into “large pyramid-shaped mounds,” American Society of Agronomy reports. Once the temperatures reach at least 131 degrees F, the bacteria die off. Windrow composting involves forming long rows with the manure and churning it regularly. This method extends the heating period and temperatures of as much as 160 degrees Fahrenheit are reached.
McAllister and his team studied which method was best and used manure from cattle that had been treated with antibiotics for the testing. The researchers discovered that “composting works best for killing bacteria with resistance genes. The mixing process also speeds up decomposition and reduces the volume of manure.”
That’s not to say stockpiling doesn’t work; it’s just not as effective given that the heat is localized to the center of the pile, so any bacteria on the outer edges is not killed off.
Future experiments are in the plans and might involve the journey of the bacteria.
“The concentration of bacteria is the issue, and if those concentrations travel. The journey for most bacteria from the animal through the environment to people is a tough one. Most bacteria do not make it. Manure management practices such as composting and stockpiling can make this journey for bacteria even more difficult,” McAllister told American Society of Agronomy.
The study, called “Dissipation of Antimicrobial Resistance Determinants in Composted and Stockpiled Beef Cattle Manure” was published in the Journal of Environmental Quality. Click here to read the whole study.
