Plant Oils Help Abate Livestock
By Ben Hardin
September 12, 2000
Foul-smelling compounds that waft from cattle feedlots may one day be abated
by chemicals called essential oils--like those produced by some minty
plants--Agricultural Research Service
The odor abatement studies done at the Roman L. Hruska U.S. Meat Animal Research
Center (MARC), Clay Center, Neb., accompany a quest for ways to preserve
manures value as a fertilizer, reduce emission of global warming gases
and decrease the prevalence of foodborne pathogens on livestock headed to
In laboratory experiments, microbiologist Vincent H. Varel used the
essential oils carvacrol and thymol in quantities as low as 1 gram in
one-half-liter slurries of cattle feces and urine to completely block formation
of foul-smelling volatile fatty acids. Using either of the two chemicals
inhibited odors in a slurry for weeks, and each was as effective as using the
oils in combination.
Carvacrol and thymol are constituents of oregano oil. 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
Varels studies also showed that these essential oils can reduce the
populations of fecal bacteria such as Escherichia coli in
slurries. Now the scientists are taking their research to manure in the feedlot
to test the essential oils against the potentially deadly bacteria E.
coli O157:H7 and other pathogens.
When pathogen-laden manure gets on the hides of cattle headed for slaughter,
the risk of meat contamination during the slaughtering process increases.
As antimicrobial agents, the essential oils may do double duty--killing
pathogens and reducing emissions of odorous compounds. Other chemicals can also
help. Urease inhibitors, for example, reduce feedlot ammonia emissions, which
contribute to odors. One such inhibitor that Varel researched had been used as
a nitrogen preservative in no-till cropping systems. Now the inhibitor is
marketed for livestock waste treatments.
ARS is the chief research agency of the U.S.
Department of Agriculture.
Scientific contact: Vincent H. Varel, ARS Roman L. Hruska U.S. Meat
Animal Research Center, Clay Center, Neb., (402) 762-4207, fax (402) 762-4209,