ARS | Publication request: Odorant production and persistence of Escherichia coli in manure slurries from cattle fed 0, 20, 40, or 60% wet distillers grains with solubles

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 2008
Publication Date: N/A

Interpretive Summary: A feeding study was conducted with 160 crossbred cattle that were fed a diet containing increasing amounts of a byproduct from ethanol production called wet distillers grains. During the process of making ethanol, many minerals and nutrients become more concentrated in the distillers grain when compared to corn. These minerals and nutrients may exceed dietary requirements of the animal when they are used as feed. Therefore, the excess minerals and nutrients from the feed can be found in the cattle manure. The objectives of the study were to determine the impact that these distillers grains have on odors, nutrients and bacteria in the cattle manure. The amount of minerals and nutrients in the manure that were converted to odor increased as the amount of distillers grains in the diets increased. It was also found that specific coliform bacteria lived longer in the manure from animals fed distillers grains. Therefore cattle feeders may have to adjust their management practices to allow for these differences when feeding distillers grains.

Technical Abstract: Ethanol production from corn removes starch and concentrates the remaining nutrients, including crude protein and minerals. When wet distillers grains with solubles (WDGS) are fed to cattle in place of corn, crude protein and minerals often exceed dietary needs. This may increase nitrogen emission, phosphorus run-off, and odor production and are evaluated in this study. Crossbred steers (n = 160; 434 kg) were assigned in a completely randomized block design to 9 x 9 m pens with concrete floor (10 animals/pen; 4 pens/trt). Steers were fed a finishing diet that contained either 0, 20, 40, or 60% WDGS on a DM basis, and provided 13.4, 14.6, 18.7, or 22.8% CP, respectively. Two kilograms of manure slurry (14 to 23% DM) were collected from each pen monthly (Aug. 20, Sept. 24, and Oct. 22). Samples were analyzed immediately for odorants, DM, pH, ammonia, total alcohol, L-lactate, and concentrations of generic Escherichia coli. After incubation of the samples at 22°C for 2, 4, 7, 10, 15, 21, and 28 d, samples were analyzed for the above characteristics plus methane production. Before incubation, ammonia, hydrogen sulfide, indole, phenol, isovalerate, isobutyrate, and acetate increased (P < 0.01) with increasing amounts of WDGS in the diet. Other odorants, skatole, caproate, valerate, butyrate, and propionate, were greater (P < 0.01) in manure slurries from cattle fed either 20 or 40% WDGS, compared to 0% WDGS. L-lactate was greater (P < 0.01) in slurries from cattle fed 0% WDGS (447 µmol/g DM) compared to the other treatment slurries (14-15 µmol/g DM). After incubation, L-lactate lowered slurry pH (6.3, 7.1, 7.6, and 8.2, respectively, for 0, 20, 40, and 60% WDGS) which inhibited microbial fermentation, E. coli persistence, and methane production. Because of the favorable pH in the 40 and 60% WDGS slurries, many of the odorant compounds were rapidly converted to methane during a 28 d static incubation. E. coli O157:H7 inoculated into subsamples of the manure slurries exhibited behavior similar to that of naturally present generic E. coli, surviving in higher numbers longer (P < 0.05) in 20 and 40% WDGS slurries than in 0% WDGS. These data indicate feeding WDGS can increase odorants in manure slurries and extend the persistence of E. coli. Key words: Distillers grains, feedlot cattle, manure, odor, E. coli, methane