Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 23, 2002
Publication Date: September 1, 2002
Citation: Miller, D.N., Varel, V.H. 2002. An in vitro study of manure composition on the biochemical origins, composition, and accumulation of odorous compounds in cattle feedlots. Journal of Animal Science. 80:2214-2222. Interpretive Summary: Substrate additions to fresh and aged feedlot manures confirmed that manure odor compounds originate primarily from starch fermentation rather than protein or other carbohydrate (i.e., cellulose) fermentation. However, protein fermentation does take on a larger role in aged manures, and can be a source of very obnoxious odor compounds. Addition of substrates to both fresh and aged manures can also impact the final composition of odor compounds with excess carbohydrate stimulating the accumulation of butyrate. Lactate accumulation in fresh manures versus aged manures was also a significant factor in the overall accumulation of total volatile fatty acid. We conclude that the ties between cattle diet, manure composition, and odor production cannot be overstated, and investigations of these relationships are paramount for better odor control at cattle feedlots.
Technical Abstract: Very little is known about the biochemical origin of cattle feedlot odors and the environmental factors controlling it. The tie between diet and manure composition is well established, but the effect of different manure compositions on odor compound production is unknown. This study describes the effect of starch, casein, and cellulose substrate additions to slurries sof fresh and aged cattle manure on the accumulation of fermentation products and the consumption of substrates relative to no addition treatments. Aged manure accumulated more VFA (245-290 mM) than the fresh manure (91-181 mM) irrespective of substrate additions. In fresh manures, VFA was increased over no addition treatments when carbohydrate (starch or cellulose) was added, whereas starch and protein treatments to aged manure increased VFA content relative to no addition treatments. Branched-chain VFA and aromatic compounds accumulated only in the aged manure (no addition nand protein treatments), an indication of some protein fermentation. Based upon substrate loss, starch fermentation was the dominant process in both manures and all treatments with losses exceeding 18.6 g/L. Protein fermentation occurred only in the aged manure when starch was no longer available. The production of odorous compounds from manure was controlled by substrate availability and pH, with pH related to lactate accumulation. Aged manure slurries had higher buffering capacity, likely due to the presence of calcareous soil and lactate-consuming microorganisms. Substrate additions had little effect on the overall accumulation of odor compounds in manure but had profound effects on odor compound composition. We conclude that modifying cattle diets to limit starch and protein excretion would profoundly affect the production and accumulation of odor compounds.