United States Department of Agriculture scientists have found that gram-positive anaerobic bacteria are often responsible for offensive odours in stored swine manure.
Now the researchers are seeking a way to help better bacteria prevail over the worst stinkers.
Gram-positive anaerobic bacteria are identified by their ability to retain particular stains or dyes. Examples include clostridia, lactobacilli and streptococci.
Microbiologist Michael Cotta and his colleagues identified the predominant bacteria in slurries from hog manure pits.
Slurries rich in bacteria associated with methane and foul-smelling compounds could become less offensive if producers treated the pits with some yet-to-be identified effective antimicrobial compounds, targeted against these bacteria.
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To the scientists’ surprise, the commercial antimicrobial compound monensin failed in laboratory research to reduce hog manure odours.
Monesin inhibits growth of gram-positive bacteria in the rumen of cows and other domestic animals to improve milk production or weight gain. But results did provide encouragement that the concept might be sound.
In their experiments, scientists used samples of manure slurry from a swine barn pit, enriched with more hog feces. They found that, in closed bottles, monensin quickly reduced methane and carbon dioxide production and continued to do so for 28 days. The amount of volatile fatty acids in the samples decreased slightly.
However, one of the foulest-smelling kind of fatty acids, butyrate, increased three-fold. So the search continues for an antimicrobial compound that will inhibit the populations of butyrate-producing microbes.
