Manure odor potential and Escherichia coli concentrations in manure slurries of feedlot steers fed 40% corn wet distillers grains.

Abstract

This study evaluated feeding 0 and 40% wet distillers grains with solubles (WDGS) diets to cattle and the effects on feedlot manure collected from soil-based pens and incubated for 28 d. Steers (n = 603; 261 +/- 32 kg) were fed in eight pens (15 x 150 m) of 75 to 77 steers per pen. Two consecutive experiments were conducted with WDGS--one in which the corn source fed with WDGS was high-moisture and one in which WDGS was fed with dry-rolled corn. We compared odorants (volatile fatty acids [VFAs], aromatic compounds, NH3, H2S) and persistence of Escherichia coli in feedlot manure slurries stored from 0 to 28 d. From both experiments, manure collected from cattle fed 40% WDGS had lower (P < 0.05) total VFAs, including acetate, propionate, and butyrate, all of which continued to be lower to 28 d. However, these slurries had greater concentrations (P < 0.05) of branched-chained VFAs (isobutyrate and isovalerate), especially after 14 d of incubations. Similarly, p-cresol and skatole concentrations tended to be greater in slurries originating from 40% WDGS diets and increased with incubation time. Indole was initially greater in the slurries from 40% WDGS diets; however, it was metabolized by microbes during incubation. Manure slurries from the 40% WDGS diets had greater quantities of H2S, NH3, and P (P < 0.05). Levels of E. coli in 0 and 40% WDGS manure slurries were similar when high-moisture corn was used in the diets. However, when dry-rolled corn was used, E. coli persisted longer in 40% WDGS manure slurries in comparison to 0% WDGS. Results here support earlier studies that suggest feeding WDGS increases odor emissions, N loss, E. coli survival, and surface water contamination due to greater potential P runoff.

Full text

Page 1

TECHNICAL REPORTS
1498
Th is study evaluated feeding 0 and 40% wet distillers grains
with solubles (WDGS) diets to cattle and the eff ects on feedlot
manure collected from soil-based pens and incubated for
28 d. Steers (n = 603; 261 ± 32 kg) were fed in eight pens
(15 × 150 m) of 75 to 77 steers per pen. Two consecutive
experiments were conducted with WDGS—one in which
the corn source fed with WDGS was high-moisture and one
in which WDGS was fed with dry-rolled corn. We compared
odorants (volatile fatty acids [VFAs], aromatic compounds,
NH3, H2S) and persistence of Escherichia coli in feedlot manure
slurries stored from 0 to 28 d. From both experiments, manure
collected from cattle fed 40% WDGS had lower (P < 0.05)
total VFAs, including acetate, propionate, and butyrate, all of
which continued to be lower to 28 d. However, these slurries
had greater concentrations (P < 0.05) of branched-chained
VFAs (isobutyrate and isovalerate), especially after 14 d of
incubations. Similarly, p-cresol and skatole concentrations
tended to be greater in slurries originating from 40% WDGS
diets and increased with incubation time. Indole was initially
greater in the slurries from 40% WDGS diets; however, it was
metabolized by microbes during incubation. Manure slurries
from the 40% WDGS diets had greater quantities of H2S,
NH3, and P (P < 0.05). Levels of E. coli in 0 and 40% WDGS
manure slurries were similar when high-moisture corn was
used in the diets. However, when dry-rolled corn was used,
E. coli persisted longer in 40% WDGS manure slurries in
comparison to 0% WDGS. Results here support earlier studies
that suggest feeding WDGS increases odor emissions, N loss,
E. coli survival, and surface water contamination due to greater
potential P runoff .
Manure Odor Potential and Escherichia coli Concentrations in Manure Slurries
of Feedlot Steers Fed 40% Corn Wet Distillers Grains
Vincent H. Varel,* James E. Wells, Elaine D. Berry, and Dan N. Miller USDA–ARS
A
uct from ethanol production (Stock et al., 2000; Klopfenstein et
al., 2008). Th is process removes starch from corn and concen-
trates the crude protein, oil, fi ber, and minerals approximately
3-fold (Spiehs et al., 2002). When these concentrated nutrients
are fed as WDGS to feedlot cattle (typically 20–40% of the diet
on a dry matter [DM] basis) in place of corn, it often results in
a diet with crude protein, oil, and minerals such as phosphorous
(P) and sulfur (S) in excess of dietary needs. Th ese excess nutrients
are excreted and can potentially contribute to environmental pol-
lution, including elevated N emission, increased P run-off , and
greater odor production (Martin, 1982). Th is was found to be
true when cattle were fi nished on WDGS diets and raised on a
concrete fl oor (Varel et al., 2008) or when cattle were fed individ-
ually wheat-based distillers grains (Hao et al., 2009). Recent stud-
ies also suggest that there is a positive association between feeding
distillers grains and fecal shedding of E. coli O157:H7 (Jacob et
al., 2008; Wells et al., 2009). Th e objectives of this study were to
evaluate, in a production-scale facility with soil-based pen fl oors,
the eff ect of WDGS fed at 0 or 40% WDGS (on a DM basis)
in two common corn-based diets on the production of malodor-
ant compounds (volatile fatty acids [VFAs], aromatic compounds,
NH3, and H2S) and the persistence of E. coli in fresh manure and
manure slurries stored from 0 to 28 d. Th e corn sources fed with
WDGS were high-moisture and dry-rolled corn.
Materials and Methods
Animals and Diets
Detailed information about the animals and diets used in this
study were previously published (Wells et al., 2009). Briefl y, the
study was initiated on 29 Oct. 2007, with 603 steers (261 ± 32
kg body weight) in eight pens (15 by 150 m) of 75 to 77 steers
per pen (four pens per treatment). Th e steers in four control pens
(0% WDGS) were fed standard diets through the growing and
fi nishing phases of production. Th e steers in the four WDGS
pens were fed similar diets, but WDGS replaced 47% of the corn
cost-effective feed resource for beef cattle is corn (Zea
mays) wet distillers grains with solubles (WDGS), a byprod-
Abbreviations: CFU, colony-forming unit; DM, dry matter; VFA, volatile fatty acid;
WDGS, wet distillers grains with solubles.
V.H. Varel, J.E. Wells, and E.D. Berry, USDA–ARS, U.S. Meat Animal Research Center,
P.O. Box 166, Clay Center, NE 68933-0166; D.N. Miller, USDA–ARS, Agroecosystem
Management Unit, Lincoln, NE 68583. Mention of a trade name, proprietary product,
or specifi c equipment does not constitute a guarantee or warranty by the USDA and
does not imply approval to the exclusion of other products that may be suitable.
Assigned to Associate Editor Søren O. Petersen.
Copyright © 2010 by the American Society of Agronomy, Crop Science
Society of America, and Soil Science Society of America. All rights
reserved. No part of this periodical may be reproduced or transmitted
in any form or by any means, electronic or mechanical, including pho-
tocopying, recording, or any information storage and retrieval system,
without permission in writing from the publisher.
J. Environ. Qual. 39:1498–1506 (2010)
doi:10.2134/jeq2009.0472
Published online 20 May 2010.
Received 1 Dec. 2009.
*Corresponding author (Vince.Varel@ars.usda.gov).
© ASA, CSSA, SSSA
5585 Guilford Rd., Madison, WI 53711 USA
TECHNICAL REPORTS: WASTE MANAGEMENT

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Varel et al.: Wet Distillers Grains in Diets Aff ect Manure Odor and E. coli
1499
grain component (DM basis) in each production phase diet
(see below). Pen manure samples were collected four times
during the fi nishing phase of the study. Th e animals received
the fi nishing diets (0% WDGS or 40% WDGS, DM basis;
Table 1) from mid-January 2008 (Day 77) until slaughter
(Day 231 or 253). Th e corn source was high-moisture corn
from October 2007 through May 2008 (Day 189). Th e supply
of high-moisture corn was depleted by May 2008; therefore,
high-moisture corn was replaced with dry-rolled corn (Day
189–253), and diets were reformulated for DM content dif-
ferences in corn source. Th e dry-rolled corn diets were fed for
a full 28-d period before the next sampling. Th erefore, during
Period 1 (high-moisture corn), all pens were sampled twice
(15 Apr. and 5 May 2008), and during Period 2 (dry-rolled
corn), all pens were again sampled twice (2 and 16 June 2008).
Manure Collection and Analyses
Manure samples were collected from three sections in each
pen. Behind the feed trough of each pen was a concrete apron
that extended into the pen 3.5 m and across the entire pen.
Th e soil area adjacent to the apron (1.2 by 15 m) was used as
the experimental area and was divided into three sections. One
composite manure sample (1 kg) was obtained from each of
the three sections per pen. Th e manure layer averaged 12 to 20
cm. Th erefore, during each sampling period (15 Apr., 5 May,
2 June, and 16 June 2008), a total of 24 1-kg samples were
obtained. Subsamples were used to determine DM, total N,
S, and P. A previous study (Spiehs and Varel, 2009) indicated
there was no diff erence in fecal DM output across treatments of
0, 20, 40, or 60% WDGS. From each 1-kg sample, 600 g was
weighed and mixed with 300 mL distilled water by blending at
high speed with a Waring blender (Waring Inc., New Hartford,
CT). Th is slurry (900 g) was poured into a wide-mouth (10
cm) jar (17 cm tall, 13.5 cm in diameter, 1.6 L volume), with
a total of 24 jars for each sampling period. Plastic lids provided
with the jars were used to cover approximately 90% of the jar
opening to minimize moisture loss over the 28-d experimental
incubation period at room temperature (22°C). Th e contents
of the jars were stirred before sampling and were sampled at
0, 2, 4, 7, 14, 21, and 28 d. Little stratifi cation of the slur-
ries occurred due to an active fermentation. Manure slurry pH
was obtained using a combination electrode and PHM 83 pH
meter (Radiometer America, Cleveland, OH). A 15-g sample
from each jar was dried at 105°C overnight to determine DM.
Another 15-g sample was acidifi ed with 15 mL of 0.5 mol L−1
H2SO4 and stored at −20°C until analyzed for fermentation
products (L-lactate, total alcohol, acetate, propionate, isobu-
tyrate, butyrate, isovalerate, valerate, isocaproate, caproate,
phenol, p-cresol, indole, and skatole). An autoanalyzer (Model
2700; Yellow Springs Instrument, Yellow Springs, OH) was
used to analyze L-lactate and total alcohol, and a gas chro-
matograph (Hewlett-Packard 6890; Agilent Technologies, Palo
Alto, CA) equipped with fl ame-ionization and mass-selective
detectors was used for all other products. Conditions used for
analyses of the products have been described previously (Miller
and Varel, 2001; Varel et al., 2008). Ammonia was determined
using a modifi cation of the Sigma Urea N kit (procedure No.
640; Sigma-Aldrich Chemicals, St. Louis, MO) (Varel and
Wells, 2007). Standards and samples were diluted 10-fold, and
5 μL was transferred to a well in a 96-well microtiter plate. Th is
was followed by additions of 50 μL of phenol nitroprusside,
50 μL of alkaline hypochlorite, and 250 μL of distilled water.
Color was allowed to develop for 20 to 30 min at room temper-
ature. Absorbance at 620 nm was measured using a microplate
reader (Ceres UV900C; Bio-Tek, Winooski, VT). Hydrogen-
sulfi de was purged from manure samples using a helium gas
stream and trapped in 7 mL of 2% (w/w) zinc acetate solution
as inert ZnS (APHA, 1965), which was subsequently measured
by the formation of methylene blue after reaction of the sul-
fi de with dimethyl-para-phenylenediamine sulfate and ferric
ammonium sulfate (Kelly and Wood, 1998). Total N, P, and S
were analyzed (Leco combustion, nitric-perchloric acid diges-
tion, and nitric acid digestion, respectively) by a commercial
laboratory (Ward Laboratories Inc., Kearney, NE).
Manure slurries were sampled at 0, 1, 2, 4, 7, 10, 14, 21,
and 28 d for the determination of E. coli concentrations. A 1-g
sample of manure slurry from each jar was weighed into a tube
containing 9 mL of buff ered peptone water (Becton Dickinson
and Co., Sparks, MD). Tube contents were mixed, deci-
mally diluted in additional buff ered peptone water if needed,
and plated onto CHROMagar ECC (DRG International,
Mountainside, NJ), using an Autoplate 4000 spiral plater
(Spiral Biotech Inc., Norwood, MA). Th e CHROMagar ECC
Table 1. Formulated rations and calculated for the fi nishing phase
diets with and without wet distillers grains with solubles fed to steers
during study.
Finishing diets†
0% WDGS‡
——— % of DM (DM basis) ———
40% WDGS
Ingredient
Corn, grain
Corn silage
WDGS
Soybean meal
Urea
Limestone
Salt
Monensin premix§
Thiamine premix¶
Vitamin supplement#
Trace mineral supplement††
Nutrient content, formulated
CP
Fat
ADF
NDF
Calcium
Phosphorus
82.75
13.75
0.00
2.40
0.40
0.57
0.062
0.030
0.023
0.008
0.007
45.15
13.75
40.00
0.00
0.00
1.04
0.000
0.030
0.023
0.008
0.000
11.86
4.05
6.83
13.89
0.403
0.293
17.86
6.32
19.48
27.38
0.451
0.339
† Fed Days 78 through 245. The 0 and 40% WDGS diets had respective
dry matter levels of 71.07 and 51.98%.
‡ ADF, acid detergent fi ber; CP, crude protein; DM, dry matter; NDF, neu-
tral detergent fi ber; WDGS, wet distillers grains with solubles.
§ Rumensin 80 (Elanco Animal Health, Indianapolis, IN).
¶ Premix contains 88 g kg−1.
# Supplement provides 8,800,000 IU of vitamin A, 880,000 IU of vitamin
D, and 880 IU of vitamin E per kilogram.
†† Supplement contains 13% Ca, 12% Zn, 8% Mn, 10% Fe, 1.5% Cu, 0.2%
I, and 0.1% Co.

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1500 Journal of Environmental Quality • Volume 39 • July–August 2010
(DRG International, Inc.) plates were incubated at 37°C for 24
h, and characteristic blue E. coli colonies were counted.
An aliquot (50 g) from the manure slurry of each pen was
transferred to a 150-mL serum bottle, gassed with N, and incu-
bated at room temperature (22°C). Methane production was
analyzed using a 8610C gas chromatograph (SRI Instruments,
Torrance, CA) as described by Miller and Berry (2005) over a
28-d period.
Statistical Analyses
Data for initial pen collections were analyzed as a split-plot
with pen as the experimental unit. An initial model was used
with all interactions, and after step-down analyses, the fi nal
model included the eff ects of period, pen, dietary treatment,
and pen nested within dietary treatment. Dietary treatment
was tested with pen nested within dietary treatment as the
error term. Data from the incubations of collected pen samples
were analyzed as a split-plot in time. Bacterial numbers were
transformed to log10 colony-forming unit (CFU) per gram of
wet weight before statistical analysis. An initial model was used
with all interactions, and after step-down analyses, the fi nal
model included the eff ects of period, pen, dietary treatment,
dietary treatment × time, and pen nested within dietary treat-
ment. Dietary treatment was tested with pen nested within
dietary treatment as the error term. When dietary treatment ×
time interaction was observed, diff erences among means were
tested with a protected t test. For all statistical analyses, diff er-
ences were considered signifi cant when the probabilities were
less than 0.05. Statistical analyses were conducted using the
GLM procedure (SAS Inst. Inc., Cary, NC).
Results
Data in Table 2 between diets with high-moisture corn and
dry-rolled corn are not directly comparable because time of
sampling and the environmental conditions confound com-
parison of the data. Samples collected on 15 Apr. and 5 May
2008 experienced cooler temperatures (3 and 8°C, respectively)
than the samples collected on 2 and 16 June 2008 (19 and
24°C, respectively). Th us, any diff erences observed between
the two corn sources may not be a result of the way the corn
was processed; rather, it may be infl uenced by the tempera-
ture (see Wells et al., 2009, Fig. 1C for all temperatures) when
samples were collected. Th erefore, the results are reported sepa-
rately for each corn source. In general, the odorants acetate,
propionate, butyrate, and total VFAs were greater (P < 0.05)
or the same when high-moisture or dry-rolled corn was fed
with no (0%) WDGS in the diet, compared with 40% WDGS
(Table 2). Th e opposite was true for the branched-chain VFAs,
isobutyrate and isovalerate; the aromatic odorants, phenol,
p-cresol, and indole; and H2S-S and ammonia-N, which were
all in greater concentrations (P < 0.05) when 40% WDGS was
fed. Th e minerals (N, P, and S) were greater (P < 0.05) in the
Table 2. Initial odorants, L-lactate, pH, nitrogen, sulfur, phosphorus, and generic Escherichia coli from manure slurries collected over four sampling
periods from cattle fed 0 or 40 wet distillers grains with solubles (n = 24).
Item
High-moisture corn Dry-rolled corn
Wet distillers grains in diet, % DM† basis
SEM0 400 40SEM
Odorant, mmol kg−1 DM
Acetate
Propionate
isoButyrate
Butyrate
isoValerate
Valerate
Caproate
Total VFAs
Phenol
P-cresol
Indole
Skatole
H2S-S, mg kg−1 DM
Ammonia-N, g kg−1 DM
pH
L-lactate, mmol kg−1 DM
Total alcohols, mmol kg−1 DM
Minerals, g kg−1 DM
Total nitrogen
Phosphorus
Sulfur
Generic E. coli
Log10 CFU g−1 wet manure
† CFU, colony-forming units; DM, dry matter; VFA, volatile fatty acid.
‡ Within corn source, means followed by diff erent lowercase letters within each row diff er (P < 0.05).
188a‡
107a
1.4a
39a
1.8a
1.3a
0.36a
339a
0.07a
0.96a
4.68a
0.49a
0.30a
1.54a
6.35a
56.4a
6.2a
158b
84b
2.6b
16b
2.6b
1.6b
0.09b
266b
0.21b
1.28b
5.23a
0.44a
7.46b
5.19b
6.87b
8.8b
0.51b
5.0
5.7
0.08
2.0
0.07
0.09
0.02
9.6
0.01
0.07
0.38
0.05
0.54
0.16
0.05
5.3
0.5
97a
72a
2.1a
61a
2.0a
4.5a
0.65a
244a
0.01a
0.47a
1.63a
0.49a
2.14a
0.85a
6.27a
3.4a
0.84a
93a
50a
2.0a
28b
2.1a
2.9b
0.10b
178b
0.08b
0.71b
2.81b
0.76b
10.19b
2.46b
6.53b
5.2b
0.49a
6.0
2.5
0.12
4.3
0.11
0.30
0.05
11.6
0.01
0.06
0.32
0.08
0.70
0.19
0.07
0.4
0.17
15.5a
4.8a
3.4a
17.6b
5.7b
4.3b
0.5
0.15
0.11
16.2a
4.8a
3.5a
18.4b
5.9b
4.1b
0.5
0.19
0.15
6.05a6.28a0.106.44a6.94s0.13

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Varel et al.: Wet Distillers Grains in Diets Aff ect Manure Odor and E. coli
1501
manure slurries when 40% WDGS was included in either of
the corn diets than when no (0%) WDGS was in the diet.
Accumulation and degradation of VFAs and aromatic fer-
mentation products from in vitro incubation of manure slur-
ries from cattle fed 0 and 40% WDGS are given in Fig. 1 and
2, respectively, for the high-moisture corn and dry-rolled corn
diets. Data in Fig. 1A through 1D indicate that all straight-
chain VFAs, with the exception of valerate, were initially lower
and continued to be lower (P < 0.05) over the 28-d incuba-
tion for the diet containing 40% WDGS. Th e opposite was
Fig. 1. Accumulation and degradation of individual and
branched-chain volatile fatty acids and aromatic fer-
mentation products from in vitro incubation of manure
slurries from cattle fed high-moisture corn with 0 or 40%
wet distillers grains with solubles (WDGS) (n = 24). DM,
dry matter.

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1502 Journal of Environmental Quality • Volume 39 • July–August 2010
true for the branched-chain VFAs. Isobutyrate and isovalerate
concentrations were greater (P < 0.05) over the 28-d incuba-
tion for the diet containing 40% WDGS with high-moisture
corn (Fig. 1E and 1F). For the dry-rolled corn (Fig. 2E and
2F), isobutyrate and isovalerate concentrations were similar
between 0 and 40% WDGS diets up to Day 14; however, at
Days 21 and 28, these concentrations were greater (P < 0.05)
for the 40% WDGS diet. Aromatic compounds in the manure
slurries initially were greater (P < 0.05) with the 40% WDGS
diet, irrespective of corn source (Fig. 1G and 1H; Fig. 2G, 2H,
and 2I), with the exception of skatole from the high-moisture
corn diet (Fig. 1I), which was the same. However, over the
28-d incubation, concentrations of indole declined with the
high-moisture and dry-rolled corn diets (Fig. 1H and 2H). Th e
Fig. 2. Accumulation and degradation of individual and
branched-chain volatile fatty acids and aromatic fermenta-
tion products from in vitro incubation of manure slurries
from cattle fed dry-rolled corn with 0 or 40% wet distillers
grains with solubles (n = 24). DM, dry matter.