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Livestock manure odor abatement with plant-derived oils and nitrogen conservation with urease inhibitors: A review¹

USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933²

Abstract

Confined animal feeding operations are under environmental scrutiny for production of large quantities of waste in a small area. The waste can result in odor, global warming gases, and the transfer of nutrients and pathogens to water and food sources. An incomplete anaerobic degradation of the carbohydrate, protein, and lipid components in waste is the primary cause of odor emissions. This incomplete degradation results in the formation of short-chain volatile fatty acids (VFA), amines and other nitrogenous compounds, and sulfur-containing compounds. Our objectives are to provide simple, cost-effective, and environmentally sound solutions to control odor and pathogens in livestock waste, with nutrient management a top priority. Previous studies have indicated that a urease inhibitor, N-(n-butyl) thiophosphoric triamide, can be used to reduce urea hydrolysis in beef cattle feedlot pens, conserve nitrogen, and inhibit ammonia emissions that contribute to odor. Our laboratory studies with antimicrobial plant-derived oils, thymol and carvacrol, at 2 g/kg of feedlot waste, demonstrated that production of VFA in flasks over 23 d can be completely inhibited. Fecal coliforms were reduced from 4.6 x 10⁶ to 2.0 x 10³ cells/mL 2 days after treatment and were undetectable within 4 d. Total anaerobic bacteria were reduced from 8.4 x 10¹⁰ to 1.5 x 10⁷ cells/mL after 2 d and continued to be suppressed to that level after 28 d. These plant oils are not degraded under anaerobic conditions. However, our feedlot studies and the literature indicate these oils are degraded under aerobic conditions. This suggests that these generally recognized as safe (GRAS) chemicals, which are routinely used as preservatives in food and personal care products, should not accumulate in soils to which this waste is applied. It is concluded that chemical additives can be added to animal waste to prevent degradation, which in turn controls odor emissions, reduces pathogens, and conserves nutrients until the waste can be recycled as fertilizer. The economics and environmental effects of using thymol and carvacrol in livestock production facilities need to be determined.

¹ The author wishes to thank ALPHARMA for sponsoring this Beef Cattle Nutrition Symposium.

² Correspondence: P.O. Box 166 (phone: 402/762-4207; fax: 402/762-4209; E-mail: varel{at}email.marc.usda.gov).