Three studies at Agriculture Canada’s research centre in Lethbridge are measuring the persistence of antibiotics in cattle manure.
Soil scientist Francis Larney is trying to determine how antibiotics behave after they are expelled in manure from cattle that were given sub-therapeutic microbials in their feed.
Results might provide guidance on which antibiotics break down fastest under southern Alberta conditions. That in turn could affect the choices producers make on the type of sub-therapeutic treatments they provide to cattle.
Researchers are taking three approaches:
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• surface spreading fresh manure on a research plot and incorporating manure on half the plot;
• putting manure in compost windrows and a similar amount into a pile;
• subjecting manure-applied soil and bedding packs from the feedlot to a rainfall simulator.
Samples from each of these approaches will be collected after specific intervals and analyzed to determine how long antibiotics persist and in what concentration.
Cattle in the research centre’s feedlot will be fed the antibiotics chlortetracycline, sulfamethazine and tylosin.
The three treatments will yield three types of manure that will be tested using the three experimental approaches.
The manure spreading experiment began last year and will continue this year, Larney said. Manure was applied last fall and monthly samples have been taken. The same thing will happen this fall.
“We’re basically just monitoring what’s happening in terms of levels of antibiotics in the soil over time,” said Larney. “We’ll sample those soils up until June.”
Early results show antibiotic dissipation as soon as manure is excreted, but more data will be collected before analysis is conducted.
An experiment that starts in June will put manure in a pile, which is common practice.
“Lots of guys just stockpile and they just let it sit, so we’re going to do an experiment where we’re going to clean out the pens. Half the manure will go to compost windrows and half will go to stockpiles and the stockpiles will just be left to sit.”
Larney researched antibiotic persistence in manure compost in 2005- 06 and now wants to expand on that study.
The runoff experiment will apply manure to one sq. metre of soil and subject it to a rainfall simulator. The resulting runoff is captured and analyzed for antibiotic residue.
“Basically if you can demonstrate that it’s coming off in the runoff, then potentially it has a pathway to get into surface water,” Larney said.
Runoff from bedding packs in feedlot pens will also be collected and tested under similarly controlled conditions.
“Theoretically, in a feedlot any runoff from the pens should end up in a catch basin. Potentially we’re looking at if there’s movement coming off bedding packs, and the manure there would be really fresh.”
The 2005-06 study found that antibiotics break down as they undergo chemical reactions and are subjected to compost activity and moisture. However, different antibiotics degrade at different rates.
“The simple act of composting or putting the manure through a composting process, you’re going to reduce your potential loadings of the antibiotic onto the land when you apply the compost, than if you went out and just applied raw manure straight to the field. This is the kind of thing we’re trying to put numbers on.”
Results are expected to be available in about a year.
