Download Feeding Value of Wheat-Based Thin Stillage: In Vitro Protein

Feeding Value of Wheat-Based Thin Stillage: In Vitro Protein Degradability
and Effects on Ruminal Fermentation
P. Iwanchysko*, J. J. McKinnon*,1, A. F. Mustafa*, D. A. Christensen*, and D. McCartney†
*Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK, S7N 5B5 and
†Agriculture and Agri-Food Canada, Lacombe, AB
ABSTRACT: Two experiments were conducted to
evaluate the nutritive value of wheat-based thin
stillage as a fluid source for ruminants. In vitro CP
degradability of thin stillage was estimated relative to
canola meal and heated canola meal in a completely
randomized design. Four ruminally cannulated steers
were used in a double cross-over design to determine the
effects of consuming thin stillage or water as drinking
sources on ruminal fermentation traits. The in vitro CP
degradability of thin stillage (55.4%) was lower (P <
.05) than that of canola meal (59.4%) and higher than
that of heated canola meal (31.6%). Ruminal pH for
steers consuming thin stillage was higher (P < .05) at
1000 and 1100 and lower (P < .05) at 1900 and 2000 than
that for steers consuming water. Total VFA followed a
pattern that was the reverse of that reported for pH.
Ruminal NH3 N levels were higher (P < .05) for steers
fed thin stillage than for water-fed steers through most
of the collection period. Ruminal fluid and particulate
matter passage rates were not affected by treatment
and averaged .165 and .06 /h, respectively. The amount
of thin stillage and water that did not equilibrate with
the ruminal fluid and, thus, was considered to bypass
the rumen was estimated to be 51.9 and 59.2% of total
fluid consumed, respectively. Feeding wheat-based thin
stillage had no adverse effects on ruminal metabolism.
Key Words: Wheat, Ethanol, Rumen Metabolism
1999 American Society of Animal Science. All rights reserved.
Introduction
Thin stillage from corn-based ethanol production
been shown to be an excellent source of nutrients for
growing and finishing cattle (Aines et al., 1987; Ham
et al., 1994). Wheat-based thin stillage was similarly
shown to enhance growth of cattle grazing crested
wheatgrass pastures (Ojowi et al., 1996). In addition to
its nutrient profile, thin stillage may influence performance by altering the site of nutrient digestion. Fisher
(1995) found that thin stillage fed as a fluid source
improved total tract digestibility of DM, CP, and NDF
of the total mixed diet. Ham et al. (1994) found similar
improvements in digestibility when thin stillage was
infused into the rumen and indicated that rumen pH
and acetate:propionate ratio were reduced. Other rumen traits that may be affected by thin stillage feeding
are ruminal fluid osmolality and ammonia N levels as
well as fluid and particulate matter passage rates. In
addition, commercial practices such as high grain feeding that lead to an increase in ruminal acid production
can decrease the efficiency of microbial protein synthe-
1
To whom correspondence should be addressed.
Received November 12, 1998.
Accepted April 6, 1999.
J. Anim. Sci. 1999. 77:2817–2823
sis (Sniffen et al., 1992). This pattern could be compounded by the low pH (i.e., 4) of thin stillage
(Fisher, 1995).
Larson et al. (1993) has shown that up to 50% of the
fluid from thin stillage bypassed the rumen. Rumen
bypass may result from inadequate mixing or activation
of the esophageal-groove reflex in growing cattle
(Ørskov, 1992). With respect to DM that is available
for ruminal bacterial fermentation, little information
exists on the degradability characteristics of thin
stillage nutrients, particularly protein. Our objectives
for this study were to define the chemical and in vitro
degradability characteristics of thin stillage protein derived from wheat-based ethanol production and to determine the effects of consuming thin stillage as a fluid
source on selected ruminal fermentation traits. A final
objective was to measure the extent that thin stillage
bypasses ruminal fermentation.
Materials and Methods
Composition and In Vitro Degradability of Thin
Stillage Protein. Thin stillage samples (n = 10) were
collected on a weekly basis from Pound-Maker Agventures Ltd., at Lanigan, Saskatchewan and analyzed for
moisture, ash, ether extract, Kjeldahl nitrogen, ADF
(AOAC, 1990), and NDF (Van Soest et al., 1991). Soluble
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IWANCHYSKO ET AL.
CP and nonprotein nitrogen content were determined
according to the procedures of Licitra et al. (1996). Variability in CP degradability of the 10 thin stillage samples was determined by incubating duplicate samples
(.2 g air-dry CP) in 10 mL of fresh protease enzyme
(protease type XIV from Streptomyces griseus; Sigma
Chemical Co., St. Louis, MO) at 39°C for 18 h (Roe et
al., 1990). The insoluble residues were then filtered
through Whatman no. 54 filter paper and residual N
was determined using the Kjeldahl method (AOAC,
1990). To estimate rumen CP kinetic parameters and
effective degradability of thin stillage, a composite sample was compiled by taking 20 g of each of the 10 samples. For comparison purposes, two additional protein
sources were included: canola meal and heated (125°C
for 10 min) canola meal. Canola meal is considered a
good source of ruminally degraded protein (Mustafa et
al., 1996), and heated canola meal is considered a good
source of ruminally undegraded protein (McKinnon et
al., 1995). The protein sources were ground through a
1-mm screen using a Retsch grinder. Duplicate samples
of each protein source containing the equivalent of .2
g air-dry CP of thin stillage, canola meal, and heated
canola meal were incubated in protease enzyme solution for 1, 2, 4, 6, 8, 12, 18, and 24 h as described
previously. In vitro CP disappearance data were fitted
to the equation of Ørskov and McDonald (1979): P = a
+ b × (1 − e−ct), where P is CP disappearance at t time,
a is the soluble CP fraction (%), b is the slowly degradable CP fraction (%), and c is the rate of degradation
(per hour) of the b fraction. The constants a, b, and c
were estimated using an iterative least squares method
applying the nonlinear regression analysis of SAS
(1989). Effective degradability of CP (EDCP) was estimated according to the equation of Ørskov and McDonald (1979): EDCP = a + [(b × c)/(c + k)], where k is the
ruminal outflow rate (.05/h), and a, b, and c are as
defined above.
Rumen Metabolism Study
Animals and Dietary Treatments. Four ruminally cannulated steers (381 ± 5.1 kg) were used in a double
cross-over design (Cochran and Cox, 1959) consisting
of four 28-d periods. The animals were housed in individual pens (3.6 × 3.6 m) in the livestock research barn
of the Department of Animal and Poultry Science at
the University of Saskatchewan. The temperature was
kept at approximately 18°C. Animals were cared for
and procedures carried out according to the guidelines
of the Canadian Council of Animal Care.
Dietary treatments included thin stillage from
wheat-based ethanol production or water as fluid
sources. The thin stillage was obtained weekly from the
same source and stored in a 2,000-L plastic container
equipped with a recirculating pump. The fluid treatments were offered to cattle in 60-L containers. Fluid
consumption was monitored daily by the use of a calibrated meter ruler. Residual fluid levels were measured
Table 1. Ingredient and chemical composition of diet
used in the metabolism and the rumen bypass trials
Item
% DM basis
Ingredient composition, % DM basis
Barley silage
Alfalfa/brome hay
Barley
Tallow
Limestone
Mineral salta
Vitamin premixb
33.7
15.4
49.1
.31
.46
.51
.65
Chemical composition, % DM basis
CP
Ash
Ether extract
NDF
ADF
11.7
7.4
4.3
44.8
23.3
a
37.8% Na, 10,000 mg/kg Zn, 75 mg/kg I, 4,050 mg/kg Fe, 6,500
mg/kg Mn, 4,000 mg/kg Cu, and 30 mg/kg Co per kg of premix.
b
440,000 IU vitamin A and 89,000 IU vitamin D per kg of premix.
each morning prior to and following the filling of the
containers. The cattle were fed a basal diet of 51% barley grain concentrate, 34% barley silage, and 15% alfalfa/brome hay (DM basis, Table 1) at 0900 and 1600
daily. During each period, the cattle had ad libitum
access to the fluids and feed for the first 2 wk, but they
were restricted to 90% of ad libitum intake during the
7 d prior to the collection period.
Rumen Sampling
Passage Rates. On d 22 of each period, each steer was
dosed intraruminally with .5 g of Co-EDTA in 50 mL
of distilled water and 100 g of chromium-mordanted
hay at 3 h prior to feeding following procedures outlined
by Uden et al. (1980). Ruminal contents were manually
emptied, thoroughly hand-mixed with the markers, and
returned to the rumen. During evacuation, ruminal contents were placed in plastic 20-L pails, covered with
aluminum foil, immersed in a water bath at 39°C, and
maintained under carbon dioxide.
Ruminal fluid was sampled via the ruminal cannula
from four sampling sites hourly for a total of 15 h after
dosing. Following removal from the rumen, the fluid
was squeezed through four layers of cheesecloth. Rumen pH was measured immediately using a Fisher pH
meter (Model 825 MP; Fisher Scientific, Pittsburgh,
PA). Aliquots of the filtrate (100 mL) were also acidified
(1 mL of 50% H2SO4) and frozen for VFA and NH3 N
analysis. Ruminal fluid samples (100 mL) for osmolality
measurements were not acidified.
Ruminal particulate and rectal fecal grab samples
were collected 3, 6, 9, 12, 15, 18, 24, 27, 31, 34, 37, 41,
44, 47, 51, 54, 57, 60, 63, 69, and 73 h after dosing with
the chromium-mordanted hay. Samples were mixed,
covered, and frozen in aluminum foil containers. Ruminal fluid, particulate, and fecal samples were collected
at 0500 for determination of baseline cobalt and chromium levels.
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THIN STILLAGE AND RUMEN METABOLISM
Rumen Bypass Study. The protocol to determine the
extent to which thin stillage or water bypasses the rumen was based on that of Larson et al. (1993). On d
27 of each period, the animals were restricted from
drinking for 12 h. The animals were given access for
15 min to 53 L of their respective fluid treatment
marked with Co-EDTA (.06 g/L). The fluid source was
then withdrawn, and the rumen of each animal was
manually emptied. Rumen evacuation was completed
within 25 min. Ruminal particulate matter was separated from the fluid by squeezing through four layers
of cheesecloth. Ruminal fluid volume was estimated
from the volume of the separated ruminal fluid. Ruminal particulate matter and fluid were then weighed,
subsampled, mixed together, and returned to the rumen. Subsamples were placed in plastic containers and
frozen. Refused fluid marked with Co-EDTA was measured, subsampled, and frozen. This procedure was carried out for each animal in each of the four periods.
Laboratory Analyses. Ruminal fluid samples were
thawed at room temperature and centrifuged at 10,000
× g for 10 min. Ruminal ammonia concentration was
determined using a Cole Parmer (Vernon Hills, IL) ammonium electrode (Model No. 27502-02). For VFA analysis, .2 mL of 25% metaphosphoric acid and .3 mL of
1% crotonic acid (internal standard) were added per
milliliter of ruminal fluid. The samples were allowed
to stand for 10 min and then centrifuged (14,000 × g
for 12 min), and the supernatant was used for VFA
analysis. Concentrations of VFA were determined with
gas chromatography (Model 5790A; Hewlett Packard,
Avondale, PA) with a Poropak Q column (Poropak, Framingham, PA). The oven temperature was 210°C, and
the injector and detector block temperature was 220°C.
Run time was 13 min.
Cobalt concentration was determined with atomic absorption spectroscopy (Model 2380; Perkin-Elmer, Foster City, CA) on supernatant from ruminal fluid samples that were centrifuged at 3,000 × g for 10 min.
Ruminal particulate matter and fecal samples were
thawed at room temperature, dried at 60°C for 3 d,
ground through a 1-mm screen, and analyzed for chromium concentration with atomic absorption spectroscopy (Model 2380, Perkin-Elmer) following nitric/perchloric acid digestion. Ruminal fluid osmolality was
measured on supernatant from thawed, nonacidified
ruminal fluid samples using a Westcor (Logan, UT)
5100C vapor pressure osmometer.
Drinking fluids and ruminal contents collected during the rumen bypass study were analyzed for Co as
described for ruminal fluid. The percentage of thin
stillage or water that bypassed the rumen was calculated using the following equation (Larson et al., 1993):
100 − [(mg of Co measured in the rumen/mg of Co consumed) × 100]. Feed samples collected during the metabolism trial were analyzed for moisture, ash, ether
extract, Kjeldahl N, ADF, and NDF as previously described.
Table 2. Chemical composition of thin stillage (n = 10)
from wheat-based ethanol production
Item
DM
Ash
Ether extract
ADF
NDF
CP
Soluble protein, % of CP
Nonprotein nitrogen,
% of CP
In vitro protein
degradability, % of CP
Level, % DM basis
SD
6.3
9.4
6.9
2.0
38.4
46.6
19.9
1.0
1.1
1.1
.2
5.9
4.9
2.09
18.7
1.44
65.1
3.8
Passage Rate Calculations and Statistical Analysis. Ruminal fluid and particulate matter passage rates were
calculated from the disappearance curves of cobalt and
chromium, respectively. Fecal passage rate was calculated from the disappearance curve of chromium in fecal
grab samples. Disappearance curves of markers were
fitted to gamma age-dependent and age-independent
two-compartment models (Pond and Ellis, 1988) using
the NLIN procedure of SAS (1989) as described by
Moore et al (1992). The order of gamma age dependency
was two for cobalt and three for chromium. The two
orders were selected because of differences in the degree
of right skewness of the disappearance curves of markers; that degree was less pronounced for curves associated with particle markers than for curves associated
with fluid markers (Luginbuhl et al., 1994). The data
were analyzed using analysis of variance techniques for
a double cross-over design including repeated measures
analysis for ruminal fluid measurements using the
GLM procedure of SAS (1989). Data from the in vitro
CP degradability incubations were analyzed as a completely randomized design (three treatments and three
replicates). Means separation was carried out where
necessary (P < .05) using the Student-Newman-Keul
procedure (Steel and Torrie, 1980).
Results and Discussion
Chemical Composition of Thin Stillage. The primary
fermentation substrate used for ethanol production in
this trial was wheat, which made up 60 to 91% of the
feedstock for fermentation. The remaining feedstock
consisted of varying proportions of triticale, corn, rye,
and barley. Despite this variation in substrate composition, the nutrient profile of the thin stillage samples
was relatively similar throughout the trial (Table 2).
Furthermore the ash, ether extract, CP, NDF, and ADF
values reported in the present study for thin stillage
were similar to values reported for thin stillage derived
from 100% wheat (Ojowi et al., 1996). The average CP
and NDF values reported in this study for wheat-based
thin stillage were higher than those of corn-based thin
stillage as reported by Larson et al. (1993) and Ham et
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IWANCHYSKO ET AL.
Table 3. In vitro CP kinetic-parameters and effective
degradability of thin stillage relative to canola meal
and heated canola meal
Protein source
Item
Soluble fraction,
% of CP
Slowly degradable,
% of CP
Degradation rate,
/h
Effective
degradability, % of CP
Thin
stillage
Canola
meal
Heated
canola meal
20.4c
39.9b
15.7d
.18
46.9
39.3
44.5
3.13
.147b
55.4c
.049c
59.4b
.029 d
31.6d
SEMa
.005
.61
a
Pooled standard error of the mean.
Means within each row with different superscripts are different
(P < .05).
b,c,d
al. (1994). Soluble CP and NPN of thin stillage averaged
19.9 and 18.7% of total CP, respectively. These results
indicate that most of the soluble CP in thin stillage is
in the form of nonprotein nitrogen.
In Vitro CP Degradability of Thin Stillage. The extremely fine particle size of dried thin stillage made it
difficult to estimate ruminal CP degradability using the
nylon bag technique. Other researchers have used in
vitro procedures based on protease enzymes to estimate
CP degradability of different protein supplements (Assoumani et al., 1992; Susmel et al., 1993). The average
in vitro CP disappearance of the 10 thin stillage samples was 65.1 ± 3.8% (Table 1). Due to the small differences between the thin stillage samples in terms of
chemical composition and in vitro CP disappearance,
the samples were pooled to form a composite sample to
estimate CP kinetic parameters and effective degradability of thin stillage relative to canola meal and heated
canola meal.
The rapidly soluble (fraction a) CP content of thin
stillage was lower (P < .05) than that of canola meal
but higher (P < .05) than that of heated canola meal
(Table 3). Canola meal has been shown to have high
soluble CP (Mustafa et al., 1996), and heating is known
to reduce this protein fraction (Mustafa et al., 1997).
Although not significantly different, the slowly degradable CP (fraction b) followed the order thin stillage >
heated canola meal > canola meal. The rate of degradation of fraction b was highest (P < .05) for thin stillage,
intermediate for canola meal, and lowest (P < .05) for
heated canola meal. The results for canola meal and
heated canola meal are in agreement with those found
by Mustafa et al. (1997). The effective CP degradability
(Table 3) of the thin stillage was higher (P < .05) than
that of heated canola meal but lower (P < .05) than
that of canola meal. The relatively high effective CP
degradability of thin stillage CP is due to its high degradation rate (Table 3). Because the effective CP degradability of thin stillage is considerably closer to that of
canola meal, one would classify thin stillage as a relatively degradable protein source for ruminants.
The kinetics of thin stillage are somewhat different
from those of most proteins. Usually proteins that are
insoluble are degraded rather slowly (Mustafa et al.,
1997). Thin stillage protein is relatively insoluble but
has a rapid rate of degradation. This would explain the
increased NH3 N levels found with thin stillage feeding
(Figure 1). However, if thin stillage has a short residence time in the rumen, the insoluble nature of this
protein could result in a considerable portion of thin
stillage DM bypassing the rumen for absorption in the
small intestine.
Fluid Intake, Rumen pH, VFA, Osmolality and NH3
N Levels. Total fluid intake was 31.5 ± 8.4 L and 33.5
± 6.4 L (P > .05) for water and thin stillage treatments,
respectively. Rumen pH averaged 6.3 ± .05 throughout
the day with no effect of treatment. There was a time
effect: pH dropped (P < .01) throughout the day (Figure
1). A significant time × treatment interaction indicates
that, when thin stillage was offered as the fluid source,
ruminal fluid pH tended to be lower during the first 12
h following feeding, with significant differences (P <
.05) noted at 1000 and 1100 (Figure 1). Thin stillage in
the present study had a pH of 3.8 and as such would
be expected to stress the rumen buffer systems when
consumed. Differences (P < .05) were also noted at 1900
and 2000; however, the effects were reversed, and the
thin stillage treatment resulted in a higher pH. These
differences may be because, during the collection period, the animals had consumed all of the stillage by
this time each day, and the effect of thin stillage on
rumen pH was no longer evident.
Total VFA concentrations followed an inverse pattern
to that of rumen pH, with levels increasing (P < .01) over
time. Even though no treatment effects were observed
when the values were averaged over the course of the
day, a time × treatment interaction indicated higher
VFA levels at 0800, 1100, and 1400 in thin stillage-fed
animals and at 2000 in water-fed animals (Figure 1).
The negative inverse relationship between rumen pH
and total VFA concentrations is well documented (Burrin and Britton, 1986; Lana et al., 1998). No differences
were noted in the molar proportions of individual VFA
or in the acetate:propionate ratio (data not shown). Weigand et al. (1974) noted that dietary regimen may
greatly influence molar proportions and ratios of VFA
as well as alter pH in the rumen of mature animals.
Therefore, with the relatively minor differences shown
in rumen pH, no differences would be expected in the
proportions of acetate and propionate. Rumen osmolality was not effected by treatment, although there was
an increase (P < .01) over time (Figure 1).
Ruminal NH3 N concentrations were found to be
higher (P < .05) for steers offered thin stillage than for
steers offered water throughout most of the collection
period (Figure 1). This indicates that thin stillage protein is highly degradable in the rumen, confirming the
results of the in vitro protease incubations. Concentra-
THIN STILLAGE AND RUMEN METABOLISM
tions of NH3 N in this study are similar to those noted
by Ham et al. (1994), who reported that animals fed
corn by-products such as wet corn gluten feed had a
ruminal NH3 N value of 14.27 mg/dL. The ruminal NH3
N values reported in this study are greater than concentrations (2 to 5 mg/dL) considered to be optimal for
microbial growth (Satter and Slyter, 1974) and are
higher than those reported by Kang-Meznarich and
Broderick (1980) for optimal fermentation (3.3 to 8.5
mg/dL). The ruminal NH3 N concentrations found in
this study would indicate that all microbial N requirements are being met with thin stillage feeding. Therefore, with a readily available carbohydrate source and
supply of appropriate precursors, microbial fermentation and protein synthesis should occur at a maximum rate.
Ruminal Fluid and Particulate Matter Passage Rates.
Ruminal fluid passage rates were not influenced by
treatment, averaging .165/h (Table 3). The values reported in this study for ruminal fluid passage rates are
within the range reported in the literature (Goetsch et
2821
al., 1987; Malcolm and Kiesling, 1990; Poore et al.,
1990). The lack of any impact of thin stillage on fluid
passage rate is somewhat surprising. Ojowi et al. (1996)
reported a 43% increase in thin stillage consumption
relative to water when consumed under grazing conditions. This large intake of fluid would be expected to
increase ruminal fluid turnover. However, as previously
reported, no differences in fluid consumption were observed in this study, in which the steers were fed in
confinement. This may explain why no effect of thin
stillage feeding was seen on fluid passage rates from
the rumen. Particulate passage rates were not affected
(P > .05) by fluid source (Table 4) and are similar to
those reported by others (Okine et al., 1989; Poore et
al., 1990; Bruining and Bosch, 1992). Fecal passage
rates were also unaffected (P > .05) by dietary treatment
(Table 4). The passage rate of particulate material from
the rumen was similar to that of the fecal matter.
Bypass Value of Thin Stillage. Within the 15-min period, steers consumed 17.1 ± .7 L and 26.2 ± 1.0 L of
the 53 L of Co-EDTA marked thin stillage and water,
Figure 1. Effects of thin stillage and water as fluid source on ruminal metabolism. *Means (± SD) are different (P
< .05).
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IWANCHYSKO ET AL.
Table 4. Effects of fluid source on ruminal fluid and
particulate matter and total tract passage rates
Fluid source
Passage rate, /h
Ruminal fluid
Ruminal particulate matter
Fecal
Thin stillage
Water
SEMa
.169
.055
.058
.161
.061
.062
.013
.004
.005
a
Pooled standard error of the mean.
respectively. Dietary treatment had no effect on rumen
bypass value. The estimated rumen bypass value for
water and fluid in thin stillage was 59.2 ± 22.9 and 51.9
± 19.6%, respectively. Similar results were found by
Larson et al. (1993), who reported that over 50% of
the corn-based thin stillage consumed had bypassed
ruminal fermentation. Similarly, Woodford et al. (1984)
reported that a high proportion of water bypassed the
rumen. These workers stated that not all of the drinking
fluids should be assumed to equilibrate with the ruminal fluid. Others have also determined that a portion
of the liquid ingested by drinking bypasses the rumen
(Garza and Owens, 1989; Zorrilla-Rios et al., 1990).
Bypass could occur by failure of thin stillage to equilibrate with rumen contents or via closure of the esophageal groove, which has been shown to function in certain
circumstances in young adults (Mikhail et al., 1988;
Ørskov, 1992). These results and those of Larson et al.
(1993) suggest that, despite considerable variations in
rumen bypass values, a considerable proportion of thin
stillage bypasses the rumen and is available for digestive processes in the lower gastrointestinal tract.
Implications
Feeding wheat-based thin stillage as a fluid source
does not seem to adversely affect rumen metabolism.
Approximately 52% of thin stillage may bypass the rumen and, thus, become available for intestinal enzymatic digestion. However, 48% of thin stillage consumed should enter the rumen and can be considered
as a good source of ruminal degradable protein. As such,
thin stillage seems to be an excellent source of protein
for ruminants, satisfying the protein requirement for
the ruminal microbes and the host animal.
Literature Cited
Aines, G., T. Klopfenstein, and R. Stock. 1987. Distillers grains. Nebr.
Agric. Res. Div. Res. Bull. MP 51. Univ. of Nebraska, Lincoln.
AOAC. 1990. Official Methods of Analysis (15th Ed.). Association of
Official Analytical Chemists, Washington, DC.
Assoumani, M. B., F. Vedeau, L. Jacquot, and C. J. Sniffen. 1992.
Refinement of an enzymatic method for estimating the theoretical degradability of protein in feedstuffs for ruminants. Anim.
Feed Sci. Technol. 39:97–116.
Bruining, M., and M. W. Bosch. 1992. Ruminal passage rate as affected by CrNDF particle size. Anim. Feed Sci. Technol.
37:193–200.
Burrin, D. G., and R. A. Britton. 1986. Response to monensin in cattle
during subacute acidosis. J. Anim. Sci. 63:888–893.
Cochran, W. G., and G. M. Cox. 1959. Experimental Designs (2nd
Ed.). John Wiley & Sons, New York.
Fisher, D. J. 1995. Evaluation of thin stillage from wheat-based ethanol production as a fluid source for growing and finishing beef
cattle. M.S. thesis. Univ. of Saskatchewan, Saskatoon.
Garza, J. D., and F. N. Owens. 1989. Effect of diet and level of
intake on rumen and solid volumes, passage rates, and water
consumption of beef cattle. Okla. Agric. Exp. Sta. MP-127. pp
77–83. Oklahoma State Univ., Stillwater.
Goetsch, A. L., F. N. Owens, M. A. Funk, and B. E. Doran. 1987.
Effects of whole or ground corn with different forms of hay in
85% concentrate diets on digestion and passage rates in beef
heifers. Anim. Feed Sci. Technol. 18:151–164.
Ham, G. A., R. A. Stock, T. J. Klopfenstein, E. M. Larson, D. H.
Shain, and R. P. Huffman. 1994. Wet corn distillers byproducts
compared with dried corn distillers grains with solubles as a
source of protein and energy for ruminants. J. Anim. Sci.
72:3246–3257.
Kang-Meznarich, J. H., and G. A. Broderick. 1980. Effects of incremental urea supplementation on ruminal ammonia concentration and bacterial protein formation. J. Anim. Sci. 51:422–431.
Lana, R. P., J. B. Russell, and M. E. Van Amburgh. 1998. The role
of pH in regulating ruminal methane and ammonia production.
J. Anim. Sci. 76:2190–2196.
Larson, E. M., R. A. Stock, T. J. Klopfenstein, M. H. Sindt, and R.
P. Huffman. 1993. Feeding value of wet distillers byproducts for
finishing ruminants. J. Anim. Sci. 71:2228–2236.
Licitra, G., T. M. Hernandez, and P. J. Van Soest. 1996. Standardization procedures for nitrogen fractionation of ruminant feeds.
Anim. Feed Sci. Technol. 57:347–358.
Luginbuhl, J.-M., K. R. Pond, and J. C. Burns. 1994. Whole-tract
digesta kinetics and comparison of techniques for the estimation
of fecal output in steers fed coastal bermudagrass hay at four
levels of intake. J. Anim. Sci. 72:201–211.
Malcolm, K. J., and H. E. Kiesling. 1990. Effects of whole cottonseed
and live yeast culture on ruminal fermentation and fluid passage
rate in steers. J. Anim. Sci. 68:1965–1970.
McKinnon, J. J., J. A. Olubobokun, A. F. Mustafa, R.D.H. Cohen,
and D. A. Christensen. 1995. Influence of dry heat treatment of
canola meal on site and extent of nutrient disappearance in
ruminants. Anim. Feed Sci. Technol. 57:243–252.
Mikhail, M., H. Brugere, H. Luke Bars, and H. W. Colvin, Jr. 1988.
Stimulated esophageal groove closure in adult goats. Am. J. Vet.
Res. 49:1713–1715.
Moore, J. A., K. R. Pond, M. H. Poore, and T. G. Goodwin. 1992.
Influence of model and marker on digesta kinetic estimates for
sheep. J. Anim. Sci. 70:3528–3540.
Mustafa, A. F., D. A. Christensen, and J. J. McKinnon. 1996. Chemical
characterization and nutrient availability of high and low fiber
canola meal. Can. J. Anim. Sci. 76:579–586.
Mustafa, A. F., J. J. McKinnon, P. A. Thacker, and D. A. Christensen.
1997. Effect of borage meal on nutrient digestibility and performance of ruminants and pigs. Anim. Feed Sci. Technol.
64:273–285.
Ojowi, M. O., D. A. Christensen, J. J. McKinnon, and A. F. Mustafa.
1996. Thin stillage from wheat-based ethanol production as a
nutrient supplement for cattle grazing crested wheatgrass pastures. Can. J. Anim Sci. 76:547–553.
Okine, E. K., G. W. Mathison, and R. T. Hardin. 1989. Effects of
changes in frequency of reticular contraction on fluid and particulate passage rates in cattle. J. Anim. Sci. 67:3388–3396.
Ørskov, E. R. 1992. Protein Nutrition in Ruminants. Academic
Press, London.
Ørskov, E. R., and I. McDonald. 1979. The estimation of protein
degradability in the rumen from incubation measurements
weighed according to rate of passage. J. Agric. Sci. 92:499–503.
Pond, K. R., and W. C. Ellis. 1988. Compartment models for estimating attributes of digesta flow in cattle. Br. J. Nutr. 60:571–595.
THIN STILLAGE AND RUMEN METABOLISM
Poore, M. H., J. A. Moore, and R. S. Swingle. 1990. Differential
passage rates and digestion of neutral detergent fiber from grain
and forages in 30, 60 and 90% concentrate diets fed to steers.
J. Anim. Sci. 68:2965–2973.
Roe, M. B., C. J. Sniffen, and L. E. Chase. 1990. Techniques for
measuring protein fractions in feedstuffs. In: Proc. Cornell Nutr.
Conf., Ithaca, NY. p 81.
SAS. 1989. SAS User’s Guide: Basics (Version 5 Ed.). SAS Inst. Inc.,
Cary, NC.
Satter, L. D., and L. L. Slyter 1974. Effect of ammonia concentration
on rumen microbial protein production in vitro. Br. J. Nutr.
32:199–225.
Sniffen, C. J., J. D. O’Connor, P. J. Van Soest, D. J. Fox, and J.
B. Russell. 1992. A net carbohydrate and protein system for
evaluating cattle diets: II. Carbohydrate and protein availability. J Anim. Sci. 70:3562–3577.
Steel, R.G.D., and J. H. Torrie. 1980. Principles and Procedures of
Statistics: A Biometrical Approach. McGraw-Hill Publishing Co.,
New York.
2823
Susmel, P., C. R. Mills, M. Colitti, and B. Stefanon. 1993. In vitro
solubility and degradability of nitrogen in concentrate ruminant
feeds. Anim. Feed Sci. Technol. 42:1–13.
Uden, P., P. E. Colucci, and P. J. Van Soest. 1980. Investigation of
chromium, cerium, and cobalt as markers in digesta. Rate of
passage studies. J. Sci. Food Agric. 31:625–630.
Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods
for dietary fiber, neutral detergent fiber, and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci.
74:3583–3597.
Weigand, E., J. W. Young, and A. D. McGilliard. 1974. Volatile fatty
acid metabolism by rumen mucosa from cattle fed hay or grain.
J. Dairy Sci. 58:1294–1300.
Woodford, S. T., M. R. Murphy, C. L. Davies, and K. R. Holmes. 1984.
Ruminal bypass of drinking water in lactating cows. J. Dairy
Sci. 67:2471–2474.
Zorrilla-Rios, J., J. D. Garza, and F. N. Owens. 1990. Ruminal fluid,
a multi-pool system? Okla. Agric. Exp. Sta. Res. Rep. MP-127.
pp 174–175. Oklahoma State Univ., Stillwater.