Americans getting to grip with slurry odours
Most members of the general public across the globe are not. And given the latest rumblings coming from across the pond courtesy of the US Agricultural Research Service, there is tremendous pressure on that august body to come up with a way of making "nature's wonder" that little bit more pleasant on the nose.

And there are now signs that the boffins working on the case may have come up with a solution. Indeed, recent trials have confirmed that the odour producing chemicals in cattle slurry can be abated by chemicals called essential oils - similar to those produced by plants of the mint family. But in a more serious vein, the research has also been carried out to find ways of maintaining the fertiliser value of slurry while, at the same time, reducing emission of global warming gases and decreasing the prevalence of food borne pathogens on dairy cattle and other ruminant livestock.

In laboratory experiments, Nebraska-based microbiologist Vincent Varel used the essential oils carvacrol and thymol in quantities as low as 1 gram in one-half-litre slurries of cattle faeces and urine to completely block formation of foul-smelling volatile fatty acids. Using either of the two chemicals inhibited odours in a slurry for weeks, and each was as effective as using the oils in combination.

"Carvacrol and thymol are constituents of oregano oil," he said

"They can also be found in thyme and many other common herbal plants. Commercially, the compounds are synthetically produced and are often minor ingredients in foods and personal care products."

Varel's studies also showed that these essential oils can reduce the populations of faecal bacteria such as E. coli in slurries. Now the scientists are taking their research to manure in cattle houses to test the essential oils against the potentially deadly bacteria E. coli O157:H7 and other pathogens.

"As anti microbial agents, the essential oils may do double duty--killing pathogens and reducing emissions of odorous compounds," explained Varel.

" Other chemicals can also help. Urease inhibitors, for example, reduce ammonia emissions, which contribute to odours."