More about antibiotics in manure


This morning my friend and fellow farmers market board member Mike Gaidelis dropped off that article I noted in the update to yesterday’s post (Antibiotics with your Organic Salad?).

The article, by Sharon Dunham in The Shepherd ( V53N11, November 2008 ) has a much clearer picture of the extent of the problem with antibiotics in manure (from beef cattle) when the manure is used in the way actual farmers use it on their fields–which is either to pile/compost it first, or to spread raw manure in late fall or early winter to boost the soil fertility for spring plantings.

This solution-oriented article in The Shepherd cites the same study (conducted by Agricultural Research Service, a scientific agency in the USDA) but in a much different way than the Environmental Health News article quoted yesterday, acknowledging that antibiotics in manure are a problem, but that:

Composting beef cattle manure, even with minimal management, can significantly reduce the concentrations of antibiotics in the manure. …The scientists found that composting manure from beef cattle could reduce concentrations of antibiotics by more than 99 percent.

Further, the article reports that the ARS scientists found both piling the manure by itself or piling it with straw were both effective in reducing those concentrations of antibiotics over a twenty-eight day period, with the straw-amended piles achieving a higher rate of decrease (75-90% for plain, 91-99% with straw). Given these high rates of deterioration (for oxytetracycline and chlorotetracycline, respectively), the scientists concluded

Although manure piles amended with straw attained higher temperatures and more rapid decreases in antibiotic concentrations, there is currently no compelling justification for producers to expend additional resources needed to achieve the more rapid rates of antibiotic removal.

They do warn, however, that:

Pathogen reduction in manure piles requires careful and consistent management to ensure all parts of the pile are treated.

After Mike and I talked about these articles yesterday, I thought it might be good to throw in some further discussion here.  The problem with articles like the one in Environmental Health News is that they don’t give a clear picture of how farmers routinely engage in practices that lessen the risk of contamination by pathogens and antibiotics.  Since fewer and fewer people are coming from farm backgrounds, that might not be clear to many folks.

Neither article cites any studies of what happens to the antibiotics in the manure when you spread the manure over the field in its raw form, but after a re-read of the Environmental Health News article, I’m thinking the numbers quoted there for antibiotic uptake in vegetable plants are from planting (or transplanting) in raw, recently-applied manure, which is a HUGE no-no.

(The USDA scientists seem to do a lot of studies on how to encourage plants to take up pathogens and drugs, which might be better left to another branch of the government (DOD?) for all the good it does us farmers.  “Um, why are you trying to get that cantaloupe to suck salmonella up into its flesh?”  “If I told you, I’d have to kill you.”)

Anyhow, raw manure spreading is done before planting, and generally at the end of a previous season in order to let the elements mellow and age the manure.  The Shepherd article does not quote this information about antibiotic uptake in vegetables planted in raw manure, most likely because that’s not what farmers actually do.

Of course, I stick to my guns about buying local.  A farmer who knows her customers, who sells to them locally and directly, has a much higher stake in keeping her products safe, and a much more direct hand in making sure of their safety.

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