Oregano plants were the botanical source for the odor- and pathogen-reducing thyme oil used in the study. Image courtesy J.S. Peterson, USDA-NRCS PLANTS Database.

Waste Management: It’s About Thyme

By Laura McGinnis
December 16, 2005

A 1,000-head cattle feedlot produces about 146 to 175 tons of wet manure every week—a problematic figure for feedlot operators and their neighbors. Despite its benefits as a natural fertilizer, manure is a source of pathogens and odor. Fortunately, Agricultural Research Service (ARS) scientists are developing a method to reduce manure’s negative properties. All they need is a little thyme.

Thymol is the active component in thyme oil, which can be extracted from a variety of plants, such as thyme and oregano. Because of its pleasant odor and natural antiseptic properties, thymol appears in a variety of products, including mouthwash and throat lozenges. ARS microbiologists Elaine Berry, Vince Varel and Jim Wells discovered that its qualities can also benefit feedlots. When applied to cattle feedlot soil in slow-release granules, thymol reduced concentrations of odor-causing volatile fatty acids (VFAs) and pathogens like coliform bacteria and Escherichia coli. Berry, Varel and Wells work in the ARS Nutrition Research Unit, part of the agency’s Roman L. Hruska U.S. Meat Animal Research Center in Clay Center, Neb.

The researchers observed even more prolonged effects in swine facilities, which might be due to the pits some swine operators employ to collect and store manure. The enclosed systems could retain more thymol than the cattle feedlots, increasing its effectiveness.

The scientists also tested less expensive compounds in the lab, including terpineol, linalool, plinol and geraniol. Most promoted reduction of VFAs and pathogens like E. coli and Salmonella. Linalool was nearly as effective as thymol in the lab, but when subjected to field studies in the feedlot, thymol outperformed it. This may have been due to dry weather conditions during the test period, the researchers speculate. They plan to conduct more tests in the spring, when feedlot conditions will more closely resemble the slurries in which the compounds were initially tested.

ARS is the U.S. Department of Agriculture’s chief in-house scientific research agency.