Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 11/12/2010
Publication Date: 4/1/2011
Citation: Miller, D.N., Varel, V.H. 2011. Origins and identities of key manure odor components. In: He, Z. editor. Environmental Chemistry of Animal Manure. Hauppauge, NY: Nova Science Publishers. p. 153-177. Interpretive Summary: Manure odors are complex mixtures of individual chemical compounds that change from site to site and with distance from a particular site. Odor compounds originate in manure, both fresh and stored, and are the result of the fermentative decomposition of substrates in the manure. A diverse group of microorganisms are involved and are in part selected by the availability of easily degraded substrates. Chief among the substrates identified are protein and starch. Fermentation of proteins result in specific suites of odor compounds, branched-chain volatile fatty acids and aromatic compounds, that when detected are indicators of protein fermentation. In beef cattle manures and soils, starch is the preferred substrate, but in swine manures protein is as important as starch for odor compound production. With these insights, studies to reduce odor through diet modification have been (and continue to be) conducted indicating the preeminent role of diet in manure odor. In the future, effective management of manure emissions will likely involve both diet manipulation and a complementary strategy of microbial inhibition of both odor compound formation (by antimicrobial plant essential oils) and urea hydrolysis (by specific urease inhibitors), but continued research is needed to identify the best practices for all manure-impacted environments.
Technical Abstract: Odor is just one of many environmental issues associated with animal manures. Odor arises from a number of different locations in animal production systems, but the chemistry and biochemical origin is similar across sites. A complex mixture of volatile organic compounds (VOC) and inorganic compounds, such as H2S and NH3, all contribute to ‘odor’. Analyzing and quantifying various aspects of odor can involve human detection panels and a variety of specialized laboratory techniques, which generally separate odor into individual odorant compounds for detection and quantification. Based upon known microbial physiologies, odor compounds may arise from several types of substrates through a variety of biochemical pathways. Field and laboratory studies of odor compounds and their production indicate that starch and protein are the predominant sources for post-excretion odor production. The contribution of starch or protein towards odor compound production varies between animal species. Diet manipulation to reduce the excretion of odor precursors may be used in the future to reduce odor emissions from animal production areas. A complementary approach to control odor emissions would involved the use of environmentally-safe, microbial inhibitors, such as plant essential oils and urease inhibitors. Controlling manure odor emissions in the future will likely involve a combination of approaches to curb both the initial production and subsequent odor production during manure storage.