Microbial ecology of stored swine manure and reduction of emissions using condensed tannins

Management practices from large-scale swine production facilities have resulted in the increased collection and storage of manure for off-season fertilization use.  Stored swine manure serves as a habitat for billions of microorganisms and is associated with the generation of odorous compounds and gaseous emissions.  These compounds are not only responsible for unpleasant odors but can also pose other problems, affecting the comfort, health and production efficiency of the animals, as well as the health and comfort of human workers.  In addition, greenhouse gas emissions may contribute to climate change.  Production of these compounds from stored manure is the result of microbial activity of the bacterial populations present during storage.  We have been studying the bacterial populations of swine feces and stored manure to develop methods to reduce bacterial metabolic activity and production of gaseous emissions, including the toxic odorant hydrogen sulfide produced by sulfate-reducing bacteria.  The predominant microorganisms present in these ecosystems are obligately anaerobic, low molecular percentage G+C, Gram positive bacteria.  There is also a smaller population of aerobic microorganisms.  Quebracho and other condensed tannins were tested for effects on total gas, hydrogen sulfide, and methane production and levels of sulfate-reducing bacteria in in vitro incubations of swine manure slurry.  Quebracho condensed tannins were found to be most effective of the tannins tested, and total gas, hydrogen sulfide, and methane production were all inhibited by greater than 90% from in vitro manure slurries.  The inhibition was maintained for at least 28 days.  Total bacterial numbers in the manure were reduced significantly following addition of quebracho tannins, as were sulfate-reducing bacteria.  These results indicate that the condensed tannins are eliciting a collective effect on the bacterial population, and the addition of quebracho tannins to stored swine manure may reduce odorous and greenhouse gas emissions.