Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2001
Publication Date: 12/1/2001
Citation: Miller, D.N., Varel, V.H. 2001. In vitro study of the biochemical origin and production limits of odorous compounds in cattle feedlots. Journal of Animal Science. 79:2949-2956.
Interpretive Summary: These studies indicate that malodorous VFA production is related to starch fermentation rather than protein or other carbohydrate (i.e. cellulose) fermentation. An immediate application of this finding is to evaluate cattle fed more digestible feeds that produce waste with lower starch contents. In theory, waste with lower starch content would produce much less objectionable VFA when fermented. Additional insights from this study suggest that soil/waste mixtures enhance VFA production by minimizing acidification during waste fermentation. Lowering the soil buffering capacity or inhibiting lactate-consuming microorganisms may decrease odor formation. Field-scale studies need to be conducted to determine the effectiveness of these proposed management strategies.
Technical Abstract: Volatile fatty acids (VFA), alcohols, and aromatic ring compounds comprise a substantial fraction of livestock odor, yet very little is known about their origins and factors controlling their production. The anaerobic production of fermentation products and consumption of substrates (crude protein, starch, and nonstarch carbohydrate) were analyzed in slurries of fresh (<24 hr) and aged cattle waste (> 1 d) over several wk. Ethanol, acetate, propionate, butyrate, lactate, and H2 were the major products of fermentation. Aged cattle waste produced more than twice the concentration of VFA during incubation than the fresh waste. Aromatic compounds (phenols, indoles, and benzoates) remained unchanged in the fresh waste, but nearly doubled in the aged waste. Production of VFA from fresh manure was inhibited when the pH fell below pH 4.5. It is likely that soil buffering and lactate-consuming microorganisms minimized acidification in the aged manure slurries. Starch availability limited VFA production in the aged manure. It was also the likely biochemical source for fermentation products in both wastes based upon the strong positive correlations between fermentation product and starch content (R = 0.959 and 0.863) and ratio of fermentation products produced to starch consumed (0.42 and 0.39) for fresh and aged manure, respectively. Nonstarch carbohydrate served an indeterminate role decreasing 4.7 and 23.4 g/L in the fresh and aged manure, respectively, while the starch content decreased by 18.6 and 22.4 g/L in the fresh and aged manure, respectively. The concentration of protein did not change. We conclude that the types of substrates in cattle manure and the feedlot soils are significant factors in the production of odors.