Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 17, 2005
Publication Date: January 19, 2006
Citation: Varel, V.H., Miller, D.N., Berry, E.D. 2006. Incorporation of thymol into corncob granules for reduction of odor and pathogens in feedlot cattle waste. Journal of Animal Science. 84(2):481-487. Interpretive Summary: These studies suggest it is possible to incorporate antimicrobial thyme oil into corncobs and therefore maintain a concentration of thymol on a feedlot surface which is effective in reducing total coliforms and odor. Limitations to the usefulness of corncobs are that they have approximately a 6% carrying capacity for thyme oil (2.5% thymol) and are bulky to handle. Another granule which would carry a higher concentration of the oil may be more effective in reducing pathogens and odor, and may require applications less than once per week, which was required with the corncobs. Cost of this treatment needs to be determined. However, we do not foresee the need to apply thymol granules year-round or over the entire feedlot surface. Application would primarily be during conditions and locations on the feedlot which have enough moisture and a temperature conducive for microbial activity.
Technical Abstract: Confined animal feeding operations can be a source of odor emissions, global warming gases, water pollution, and food contamination. Laboratory studies have indicated plant oils with antimicrobial activity can be used to control pathogens and odor emissions from cattle and swine wastes. However, these oils are aromatic and may volatilize when topically applied. Our objectives were to evaluate the volatility of thymol from a feedlot surface and the effectiveness of topically applying thyme oil (2.5% thymol) incorporated into corncob granules, added once per week, to control odor emissions and total coliforms in feedlot manure. In the first study, thymol either volatilized or was degraded within 28 d after topical application. In a second study, thyme oil (2.5% thymol) was incorporated into corncobs and applied to pen surfaces weekly. Manure samples from six locations in each pen were collected from three untreated and three thymol-corncob treated pens (15 x 150 m; 50 400-kg cattle/pen), three times per week for eight weeks. Samples were analyzed for thymol concentration, VFA, branched-chain VFA and aromatic compounds, and number of Escherichia coli and total coliform bacteria. Over the eight weeks, with the exception of wk 7, the desired thymol concentration of 15 to 20 micromoles/g DM was maintained in the manure. Concentrations of VFA and branched chain-VFA increased over time in untreated and treated pens. However, rate of VFA accumulation in treated pens, 7.5 +/- 1.3 micromol/g DM**-1/wk**-1, was less than the rate of accumulation in untreated pens, 18.0 +/- 2.1 micromol/g DM**-1/wk**-1 (P < 0.01). Likewise, rate of branched-chain VFA accumulation in treated pens, 0.31 +/- 0.04 micromol/g DM**-1/wk**-1, was less than untreated pens, 0.55 +/- 0.06 micromol/g DM**-1/wk**1 (P < 0.01). Concentrations of E. coli in treated pens, 2.9 +/- 1.2 x 10**5 cfu/g DM**-1, were 91% less than untreated pens, 31.1 +/- 4.0 x 10**5 cfu/g DM**-1 (P < 0.04). Similarly, concentrations of coliforms in treated pens, 3.7 +/- 1.3 x 10**5 cfu/g DM**-1, were 89% less than untreated pens, 35.3 +/- 4.2 x 10**5 cfu/g DM**-1 (P < 0.04). These results indicate odor emissions and total coliforms can be reduced in feedlot manure with a once per week application of thymol incorporated in a granular form. However, corncobs are bulky and other granular carriers with a greater carrying capacity for thyme oil should be explored.