Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2003
Publication Date: 8/1/2003
Citation: MILLER, D.N., VAREL, V.H. SWINE MANURE COMPOSITION AFFECTS THE BIOCHEMICAL ORIGINS, COMPOSITION, AND ACCUMULATION OF ODOROUS COMPOUNDS. JOURNAL OF ANIMAL SCIENCE. 2003. v. 81. p. 2131-2138.
Interpretive Summary: Starch and protein are the primary sources of odor compounds produced during manure fermentation. The contribution of starch or protein to odor production differs between animal manures and determines the composition of malodorous compounds. Starch fermentation dominates in cattle manure fermentation, whereas both protein and starch fermentation occurs in swine manure. Protein fermentation tends to produce more offensive compounds (branched-chain volatile fatty acids and aromatic ring compounds) with low detection thresholds. This research emphasizes the strong tie between diet, manure composition, microbial fermentation, and odor production. Limiting starch excretion in cattle and both protein and starch excretion in swine through diet should help control the production of odors during manure storage. Manipulating swine and cattle diets to better manage odors originating from confined animal feeding operations will be a critical issue for animal production in the future.
Technical Abstract: Odors from swine production facilities are associated with the storage and decomposition of manure. Diet is linked to manure composition and will likely impact odor, but the microbial mechanisms responsible for manure decomposition and odor production are poorly understood. In order to identify the sources of odor during manure fermentation, substrates (starch, casein, and cellulose) were added to slurries of fresh swine manure, and the anaerobic accumulation of fermentation products and the consumption of substrates were measured relative to no addition treatments. Volatile fatty acids and alcohols were the dominant fermentation products in all treatments. The VFA concentration from starch treatment was greater (P < 0.001) than all other treatments. Branched-chain VFA and aromatic compounds accumulated in all treatments, but accumulation in the casein treatments was greater (P < 0.001) than all other treatments. Thus, addition of carbohydrate to swine manure slurries did not circumvent protein fermentation, as was previously observed in cattle manure slurries. Based upon substrate loss, starch and protein fermentation were equivalent in all treatments with losses of each exceeding 4% of the DM. Substrate additions had a limited effect on the overall accumulation of odor compounds in manure and on odor compound composition. Compared to the fermentation of fresh cattle manure, swine manure fermentation produced less lactate and more products of protein fermentation (branched-chain VFA and aromatic ring compounds). Differences in manure organic matter composition between cattle and swine, a result of diet and digestion, obviously select for bacteria that are functionally adapted to the available substrate composition. Thus, the observed preference for starch fermentation in cattle manure is the result of available starch, whereas simultaneous protein and starch fermentation in swine manure is the result of less starch and more available protein.