Plant Oils Help Abate Livestock Odors

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 scientists report.

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 manure’s value as a fertilizer, reduce emission of global warming gases and decrease the prevalence of foodborne pathogens on livestock headed to slaughter.

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 care products.

Varel’s 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, varel@email.marc.usda.gov.