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

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 × 10⁶ to 2.0 × 10³ cells/mL 2 days after treatment and were undetectable within 4 d. Total anaerobic bacteria were reduced from 8.4 × 10¹⁰ to 1.5 × 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.

Implications

Livestock production has changed over the last few decades and is now challenged with environmental and food safety issues. Nutrient management, odor emissions, and pathogenic microorganisms associated with livestock must be resolved with safe and cost-effective treatments. This requires a multidisciplinary approach and one solution is not universal to all production facilities. Microorganisms play a central role in many of the production issues, and therefore microbial activities should be addressed. Chemical additives that affect key metabolic pathways (urea hydrolysis), or additives that serve as antimicrobial agents (plant-derived oils), may offer multiple solutions for sustainable livestock production. Additives must be thoroughly evaluated and tested before one can expect producers to use them on a broad basis.

Key Words: Animal Wastes, Essential Oils, Odors, Pathogens, Urease Inhibitors

© 2002, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 80(E-Suppl. 2):E1-E7