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This Article Full Text (PDF) All Versions of this Article: jas.2008-1118v1 86/12/3617    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Varel, V. H. Articles by Koohmaraie, M. Search for Related Content PubMed PubMed Citation Articles by Varel, V. H. Articles by Koohmaraie, M.

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

V. H. Varel^*, J. E. Wells^*, E. D. Berry^*, M. J. Spiehs^*, D. N. Miller, C. L. Ferrell^*, S. D. Shackelford^* and M. Koohmaraie

^* USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933 USDA-ARS, Agroecosystem Management Unit, Lincoln, NE 68583

vince.varel{at}ars.usda.gov

Abstract

Corn ethanol production removes starch and concentrates the remaining nutrients, including CP and minerals. When wet distillers grains with solubles (WDGS) are fed to cattle in place of corn, CP and minerals often exceed dietary needs. This may increase N emission, P run-off, and odor production. These parameters are evaluated in this study. Crossbred steers (n = 160; 434 ± 8 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 13.3, 15.5, 20.6, or 24.9% 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, NH₃, total alcohol, L-lactate, and concentrations of generic E. coli. After incubation of the samples at 22°C for 2, 4, 7, 10, 15, 21, and 28 d, samples were analyzed for methane production in addition to the above characteristics. Before incubation, NH₃, H₂S, indole, phenol, isovalerate, isobutyrate, and acetate increased (P < 0.01) with increasing amounts of WDGS in the diet. Other odorants, including 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 to 15 µmol/g DM). After incubation, L-lactate contributed to 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, more neutral 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 greater 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 • E. coli • feedlot cattle • manure • methane • odor