Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol83.Issue3-4.Mar2000:
Animal Feed Science and Technology
83 (2000) 313±323
Rumen degradation in sacco in sheep of wheat straw
treated with calcium oxide, sodium hydroxide and
sodium hydroxide plus hydrogen peroxide
A.S. Chaudhry*
Department of Agriculture, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK
Received 7 June 1999; received in revised form 28 September 1999; accepted 22 October 1999
Abstract
This split unit study involved two sheep, seven incubation times and four test straws to compare
with untreated straw the effect, kgÿ1 straw dry matter (DM), of CaO (160 g CaO plus 2 l of water),
NaOH (80 g NaOH in 3 l of water) and alkaline hydrogen peroxide (NaOH plus 132 g H2O2 in 3 l
of water, AHP) treatments on composition and rumen degradation in sacco of wheat straw in sheep.
After 14 days of storage, each straw was mixed with molasses, dried, ground, weighed into nylon
bags and incubated ruminally for various hours in sheep fed daily 1 kg dried grass cubes. After
removal, the residues within bags were washed together with unincubated samples (0 h) of straws,
dried and analysed for DM, organic matter (OM) and neutral-detergent ®bre (NDF) to estimate
nutrient disappearance from straws. The data on nutrient disappearance were ®tted exponentially to
estimate quick- (a), slow (b) and predicted (P0.025) degradable fractions and degradation rate (c) for
b. NDF and hemicellulose were reduced in treated compared with untreated straw (p < 0.001).
Disappearance of nutrients from treated straws was signi®cantly greater than that from untreated
straw at almost all incubations (p < 0.001). The a, b, c and P0.025 estimates were signi®cantly
increased by all treatments (p < 0.001). AHP treatment increased straw degradation more than
NaOH and CaO treatments. Although, CaO improved rumen degradation less than NaOH, its use to
increase straw digestion even moderately may be more desirable because it is readily available,
cheap and less dangerous for the users and the environment. # 2000 Published by Elsevier Science
B.V. All rights reserved.
Keywords: Rumen degradation; Straw; Calcium oxide; Sodium hydroxide; Hydrogen peroxide
*
Tel.: 44-1912226869; fax: 44-1912227811.
E-mail address: a.s.chaudhry@newcastle.ac.uk (A.S. Chaudhry).
0377-8401/00/$ ± see front matter # 2000 Published by Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 1 3 4 - 0
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
1. Introduction
Rumen degradation is critical in the utilization of cereal straws by ruminant animals.
However, using straws as an energy feed for ruminants is limited because their cell walls
contain three dimensional structures that are less available for microbial degradation in
the rumen (Wilkie, 1979; Sundstol and Owen, 1984; Chaudhry, 1998a). Consequently,
major nutrients from straws escape digestion and are wasted as faeces by the ruminants.
However, the energy value of straws can be increased if their cell wall structure is
modi®ed. Chemical treatments can modify cell wall to increase microbial degradation
and thus utilization of straws by ruminants (Jung et al., 1993).
Recently, Chaudhry (1997) following reports from Gould (1984) and Kerley et al.
(1986) con®rmed the effectiveness of alkaline hydrogen peroxide (NaOH H2O2, AHP)
to modify cell wall composition and in vitro dry matter digestibility (DMD) of wheat
straw. However, the need for a high amount (13 or 26 l kgÿ1 DM) of water and NaOH to
maintain the pH of AHP around 11.5 was considered a limitation for the on-farm
application of AHP. In another series of in vitro experiments, although the amount of
water was reduced, the use of calcium oxide (CaO) as an alternative alkali to maintain the
ef®cacy of AHP treatment even at a pH of 11.5 did not succeed (Chaudhry, 1998b). In
contrast, CaO alone increased the in vitro DMD of wheat straw under speci®c conditions.
In another study, Chaudhry (1998c) supported the ef®cacy of CaO and NaOH alone and
AHP in improving composition, nutrient digestion and fermentation of straw-based diets
in sheep. The increased digestion was perhaps due to the increased rate and extent of
straw degradation by rumen microbes. However, this assumption can only be
substantiated if the rumen degradation kinetics were studied. Moreover, as Chaudhry
(1998c) fed each straw together with a concentrate to sheep, it was not clear whether the
increased digestion was solely a consequence of a chemical treatment or was partly due to
its interaction with the concentrate.
Since rumen is the primary site of digestion for ®brous feeds in ruminants, it is
important to monitor degradation kinetics in response to modi®cation of cell wall caused
by alkali treatments. This may be achieved by using in sacco technique which is quicker
and cheaper than whole animal studies. Therefore, this study examined the effect of CaO,
NaOH and AHP on the rate and extent of degradation in sacco of wheat straw in sheep.
Treatment with CaO was tested as a cheap and a safe alternative to NaOH in improving
the rate and extent of straw degradation whereas NaOH also served as a control for AHP.
2. Materials and methods
2.1. Chemicals, straw and treatments
NaOH (32% w/w, speci®c gravity 1.35) and H2O2 (27.5% w/w, speci®c gravity 1.1) as
solutions and CaO as a ®ne powder were purchased from, respectively, Ellis and
Everrard, and BDH, UK and used to treat wheat straw variety Norman (straw, chopped
through an 8 mm sieve) as described by Chaudhry (1998c). Each treatment was applied
on kgÿ1 straw DM basis as described below:
A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
315
2.1.1. Control
Untreated straw served as a control.
2.1.2. CaO
The straw was mixed with 2 l of water in a mixer, dusted with 160 g CaO and the
contents were then re-mixed for ca. 1 h. The treated straw was then placed into a plastic
bag, tied up and stored at ca. 128C. The added amount of CaO was 160 g kgÿ1 straw DM
with a liquid : straw ratio of 2 : 1 and an initial pH of >13.
2.1.3. NaOH
The straw was mixed with 3 l of solution containing 80 g NaOH for ca. 1 h, placed into
a plastic bag and stored as described above. The added amount of NaOH was 80 g kgÿ1
DM at a liquid : straw ratio of 3 : 1 with an initial pH of >12 during 1 h of mixing. The
NaOH-treated straw also served as a control for AHP-treated straw.
2.1.4. AHP
Another batch of NaOH-treated straw was prepared as described in Section 2.1.3. After
27 h pre-soaking, 480 ml of H2O2 solution containing 132 g H2O2 were added, mixed for
5 h and stored as described earlier. During mixing, the pH of treated straw was monitored
at 30-min intervals and was observed to remain around 11.5 0.2. The amounts of added
NaOH and H2O2 were 80 and 132 g kgÿ1 straw DM, respectively.
2.2. Preparation of straws for rumen incubation
After 14-days storage in an open shed (average temperature 128C), each kg DM of
each treated and untreated straw was separately mixed with 100 g molasses (Molaferm50; United Molasses) in line with that described by Chaudhry (1998c). No other reason
for adding molasses into straws is offered. As hot water was added into molasses to
facilitate mixing, the molasses DM was reduced from 65 to 55% and hence the added
molasses in straw on DM basis was 55 g kgÿ1. The straws were dried and ground through
a 4 mm sieve before in sacco rumen incubations.
2.3. Animals, housing and feeding
Two Suffolk Mule wether sheep weighing between 60 and 64 kg were used in this
experiment. The sheep were ®tted with rumen cannulae and housed individually on
concrete ¯oors covered with sand. Each sheep was adapted to a ®xed daily intake of 1 kg
dried grass cubes containing 160 g crude protein for 14 days before in sacco degradability
was examined.
2.4. Experimental design and chemical analysis
A split-unit design involved two sheep (blocks), seven incubation times (main units)
and four test straws (sub-units) to study in sacco degradability of untreated and treated
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
straws. Duplicate samples of ca. 2.5 g DM of each test straw were weighed into separate
nylon bags which were then tied up by a plastic string to a 16 cm long ¯exible
polypropylene tube and suspended in the rumen of each sheep for 6, 12, 24, 48, 72 and
96 h. Given the limited rumen capacity of sheep, the samples were incubated as groups so
that only one group of four straws in duplicate was incubated in the rumen at any given
time. Samples of 0 h representing water-soluble fraction (a) were prepared by washing
bags, in duplicate, containing test straws for 30 min in a domestic washing machine.
After removal from the rumen at each incubation time, the residues within bags were
washed, freeze dried, ground through a 1 mm sieve and analysed together with
unincubated samples for DM, organic matter (OM) and neutral detergent ®bre (NDF)
(Van Soest et al., 1991). Disappearance of nutrients from each straw was calculated by
difference between nutrient composition of the unwashed and unincubated dried sample
of that straw and its residue after each incubation time in the rumen. Disappearance was
assumed to be due to degradation in the rumen. Samples of unwashed and unincubated
straws were also analysed for acid-detergent ®bre (ADF) and acid-detergent lignin (ADL)
to estimate cellulose and hemicellulose contents for each straw by subtracting ADL from
ADF and ADF from NDF, respectively.
2.5. Calculations and statistical analysis
The data from in sacco studies were ®tted into the exponential model
{p ab(1 ÿ eÿct)} of érskov and McDonald (1979) by using the Maximum
Likelihood Programme to obtain estimates of a, b and c for each straw in each sheep.
Here, a represented water-soluble (or quickly degradable) and b insoluble (or slowlydegradable) fractions whereas c degradation rate of b and t the hours of incubation. While
apparent degradability was represented by a b (asymptote), predicted rumen
degradability (P0.025) for each straw was also calculated from an equation,
P a (bc/c k), where k was the rumen out¯ow rate at 0.025 per hour (h) for
animals fed at a slightly above maintenance level (AFRC, 1993). The estimates of a, b, c,
asymptote and P0.025 were statistically analysed by using ANOVA in GENSTAT to test
the effect of chemical treatments on cell wall composition and the rate and extent of in
sacco degradability of straw.
3. Results
3.1. Cell wall composition
Table 1 presents mean cell wall composition of untreated and treated straws together
with their standard errors of differences (SED). All treatments reduced NDF and
hemicellulose contents in straw compared with untreated straw (p < 0.001). However,
CaO reduced NDF content more than NaOH and AHP did (p < 0.001). In contrast,
cellulose content was increased by all treatments whereas lignin content was increased by
NaOH and AHP (p < 0.05) but decreased by CaO (p < 0.05).
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
Table 1
Cell wall composition (g kgÿ1 OM) of molassed untreated and treated straws
Composition
Neutral detergent ®bre
Cellulose
Hemicellulose
Lignin
Straw treatmentsa
Untreated
CaO
NaOH
AHP
SED
841
451
259
104
676 c
528 b
29 b
92 d
781 b
533 b
67 b
129 a
776
562
23
115
16
13
26
4
a
c
a
c
b
b
b
b
a
Untreated, CaO, NaOH and AHP were respectively, untreated, CaO-, NaOH- and alkaline hydrogen
peroxide (NaOH H2O2, AHP) treated wheat straw. After 14-days storage at 128C, molasses was added to each
straw at 55 g molasses DM kgÿ1 straw DM; neutral detergent ®bre represented total cell wall; means with
different superscripts in a same row were signi®cantly different.
3.2. Nutrient disappearance
Figs. 1±3 illustrate the patterns of DM, OM and NDF disappearance from each test
straw during rumen incubation for various times together with SED for each incubation
Fig. 1. Pattern of disappearance of dry matter (DM) from molassed wheat straw, untreated (Untr) or treated
respectively with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubation for various
times in sheep. The lines represent data being ®tted for each test straw according to the exponential model. The
standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 6, 29, 18, 14, 26, 19 and 5,
respectively.
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
Fig. 2. Pattern of disappearance of organic matter (OM) from molassed wheat straw, untreated (Untr) or treated
respectively, with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubations for
various times in sheep. The lines represent data being ®tted for each test straw according to the exponential
model. The standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 9, 25, 32, 15, 18, 21
and 16, respectively.
time. The disappearance of DM, OM and NDF was signi®cantly greater for treated
straws than for untreated straw at almost all incubation times (p < 0.001). The incubation
at 6 h was an exception where disappearance of NDF from CaO-treated straw was
not signi®cantly greater than that of untreated straw. However, the loss of NDF from CaOtreated straw on washing with water was less than untreated straw (p < 0.001). In
contrast, the losses of DM and OM from treated straws on washing with water (0 h)
were greater than that from untreated straw. Signi®cant differences between treatments
for the disappearance of DM, OM and NDF during each incubation time were also
observed (p < 0.001). AHP treatment caused the greatest disappearance of DM, OM and
NDF from straws followed by NaOH and CaO. Untreated straw showed increased
disappearance of DM, OM and NDF with increasing incubation time to 96 h (p < 0.001).
In contrast, the disappearance of nutrients from NaOH and AHP straws almost peaked at
48 h whereas the disappearance from CaO straw continued to increase to 72 h
(p < 0.001).
A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
319
Fig. 3. Pattern of disappearance of neutral detergent ®bre (NDF) from molassed wheat straw, untreated (Untr) or
treated, respectively with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubation for
various times in sheep. The lines represent data being ®tted for each test straw according to the exponential
model. The standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 7, 35, 31, 15, 20, 26
and 7, respectively.
3.3. Degradation characteristics
Table 2 presents estimates of a, b, a b, c and P0.025 for untreated and treated
straws.
3.3.1. Quickly (a) and slowly degradable (b) fractions
Quickly- and slowly-degradable fractions for DM, OM and NDF were signi®cantly
affected by treatments (p < 0.001). Quickly degradable fractions of DM, OM and NDF
were greatest for AHP treated straw compared with untreated or other treated straws
(p < 0.001). In contrast, the slowly degradable fractions of DM and NDF and OM were
greatest respectively for CaO- and NaOH-treated straws. However, the quickly
degradable fraction of NDF in untreated straw was greater compared with NaOH- and
CaO-treated straws (p < 0.01) but was less in all straws compared with AHP-treated straw
(p < 0.01).
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
Table 2
Degradable fractions of nutrients (g kgÿ1) in molassed untreated, CaO-, NaOH- and AHP-treated wheat straws
after in sacco rumen incubations in sheep (Means with standard error of difference, SED)a
Parameters
Untreated
CaO
NaOH
AHP
SED
Dry matter
a
b
c (per hour)
ab
Pat 0.025
108
433
0.015
541
274
279
644
0.021
923
573
278
599
0.049
877
675
383
559
0.054
942
765
4.6
15
0.002
18
8
Organic matter
a
b
c (per hour)
ab
P0.025
113
444
0.014
557
272
199
643
0.034
842
570
189
674
0.049
863
635
290
644
0.051
934
722
9
20
0.002
20
10
Neutral detergent ®bre
a
b
c (per hour)
ab
P0.025
65
493
0.012
558
225
ÿ34
842
0.036
808
463
23
822
0.048
845
563
111
811
0.054
922
665
10
95
0.005
89
26
a
AHP, alkaline hydrogen peroxide (NaOH H2O2); a and b respectively, quickly and slowly degradable
fractions; c, degradation rate of b; a b and P0.025 represent apparent (asymptote) and predicted extent of
degradation, respectively.
3.3.2. Degradation rate (c) and predicted degradability (P0.025)
The degradation rates of DM, OM and NDF were signi®cantly faster for treated
compared with untreated straw (p < 0.001). However, AHP treatment increased
degradation rates most compared with NaOH and CaO. Predicted degradability of DM,
OM and NDF was signi®cantly greater for treated compared with untreated straw
(p < 0.001). However, predicted degradability was greatest for AHP (p < 0.001)
compared with NaOH and CaO.
4. Discussion
Following previous studies (Chaudhry, 1998b, c), this study examined the effects of
already determined best levels of CaO, NaOH and AHP treatments on rumen degradation
in sacco in sheep. While treatments modi®ed cell wall composition and increased in
sacco rumen degradation of straw compared with untreated straw, the extent of increase
depended on the type of chemical used. The reasons for those differences between
treatments are discussed by comparing the results with published information.
The reduction in NDF by different treatments was mainly due to the decreased
hemicellulose content of straw (Table 1). The chemical treatments may have removed
some linkages within hemicelluloses and thus enhanced their solubility in detergent
A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
321
solutions (Wilkie, 1979; Chaudhry, 1998a, c). The modi®ed cell wall composition of
straw in response to NaOH and AHP was comparable to that of Chaudhry (1997, 1998c)
for the same levels of those chemicals. However, the absolute NDF in untreated and
NaOH and AHP-treated straws of this study were greater than those of Chaudhry (1997).
The variation in NDF was perhaps due to the use of different straw variety and method by
Chaudhry (1997).
The ranking of untreated and treated straws based on an increased in sacco degradation
was comparable to those of in vitro (Chaudhry, 1998b) and in vivo (Chaudhry, 1998c)
digestibility of straw treated with the same chemicals. However, the absolute degradation
for various straws differed with the change in chemicals and incubation times. The NDF
disappearance from straws was relatively less than those of DM and OM during all
incubation times. The difference between losses of different nutrients was larger during
the initial 12 h of incubation. The NDF loss from untreated straw (368 g kgÿ1) after
rumen incubation of 96 h was less than that (500 g kgÿ1) of Miller and Oddoye (1989) for
the same incubation time. The degradation rate (c, 0.012) for NDF was also slower than
that (0.042) of the same researchers. The difference may be attributed to the difference in
straw variety (Huntingdon and Givens, 1995), particle size (Hovell et al., 1987), and
rumen conditions and diet composition of the host animal (Ramanzin et al., 1997). In
general, the degradation pattern for untreated and NaOH and AHP-treated straws of this
experiment agreed with published studies (Bharghava et al., 1989; Adebowale et al.,
1989). The nutrient disappearance from CaO-treated straw was reasonably close to that
from NaOH-treated straw at 72 h of incubation and thereafter. However, the degradation
pattern of CaO of this study cannot be compared with that in the literature because almost
no published information on the degradation pattern of CaO-treated straws could be
found.
The a b value (541 g kgÿ1) for DM in untreated straw of this study was comparable
to that (599 g kgÿ1) reported by Adebowale et al. (1989). The a b value for DM in CaO
was greater compared with NaOH. This represented the greater washing loss in water of
residual CaO from straw simply because more CaO than NaOH was initially used to treat
the straw. However, it is noted that this variation was not caused by the washing loss of
added molasses since the same amounts of molasses were added across treatments. The
a b values of OM and NDF for CaO and NaOH were closer to each other despite
signi®cantly different degradation rates (c values, 0.034 vs. 0.049 for OM; and 0.036 vs.
0.048 for NDF). The non-signi®cant difference between CaO and NaOH for the apparent
extent of degradation (a b or asymptote) in this study, was comparable to that of in vitro
digestibility (Chaudhry, 1998b) but was contrary to the in vivo digestibility (Chaudhry,
1998c) where NaOH was better than CaO. However, when degradation (c) and rumen
out¯ow rates (k) were taken into consideration, the differences between the predicted
degradability (P0.025) of different straws were comparable to those of in vivo digestibility
(Chaudhry, 1998c). The decreased losses of DM and OM from untreated and DM from
CaO at 6 h were perhaps due to the particle-associated microbes that increased residual
weights of straw during incubation.
AHP was the most effective treatment in improving degradation of wheat straw. The
results agreed with the previous reports where AHP was better than its NaOH-control and
CaO in improving in vitro and in vivo digestibility of wheat straw (Chaudhry, 1997,
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
1998b, c). Although CaO greatly reduced NDF and lignin of straw, it did not improve
rumen degradation as much as NaOH and AHP did. It may be due to the greater effect of
CaO on the lignin molecule (Table 1) to release phenolics to inhibit rumen microbes and
consequently rumen degradation of straw (Marvin et al., 1996). In contrast, Silanikove
(1994) reported a greater deligni®cation in cotton straw when NaOH instead of CaO was
used as an alkali in AHP treatment. However, no difference was reported between the two
chemicals for in vitro digestibility of cotton straw. Chaudhry (1998a, b, c), has discussed
the potential and problems associated with chemical treatments in improving nutritive
value of cereal straws. In summary, the study supported the hypothesis that the increased
digestion of cereal straws by ruminants was a consequence of increased rate and extent of
their rumen degradation.
In conclusion, CaO modi®ed cell wall composition and increased rumen degradation in
sacco of wheat straw and therefore could be used as an alternative to NaOH to increase
the digestible OM intake of sheep fed treated straw. Although CaO improved rumen
degradation less than NaOH did, its use to increase straw digestion even moderately may
be more desirable because it is readily available, cheap and less dangerous for the users
and the environment. However, it is essential to reduce the level of chemicals but without
reducing their effect to improve straw digestion in ruminants. It is also essential to
perform a cost-bene®t analysis before applying treatment on-farm to improve low quality
forages. The bene®ts of using chemical treatments would be determined by the
availability and price of other animal feeds in different regions of the world at a particular
time.
Acknowledgements
ASC thanks Dr. E.L. Miller for his invaluable advice and comments during studies at
the University of Cambridge, UK and Mr. Allan Lisle from the University of Queensland
at Gatton, Australia for his statistical advice.
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83 (2000) 313±323
Rumen degradation in sacco in sheep of wheat straw
treated with calcium oxide, sodium hydroxide and
sodium hydroxide plus hydrogen peroxide
A.S. Chaudhry*
Department of Agriculture, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK
Received 7 June 1999; received in revised form 28 September 1999; accepted 22 October 1999
Abstract
This split unit study involved two sheep, seven incubation times and four test straws to compare
with untreated straw the effect, kgÿ1 straw dry matter (DM), of CaO (160 g CaO plus 2 l of water),
NaOH (80 g NaOH in 3 l of water) and alkaline hydrogen peroxide (NaOH plus 132 g H2O2 in 3 l
of water, AHP) treatments on composition and rumen degradation in sacco of wheat straw in sheep.
After 14 days of storage, each straw was mixed with molasses, dried, ground, weighed into nylon
bags and incubated ruminally for various hours in sheep fed daily 1 kg dried grass cubes. After
removal, the residues within bags were washed together with unincubated samples (0 h) of straws,
dried and analysed for DM, organic matter (OM) and neutral-detergent ®bre (NDF) to estimate
nutrient disappearance from straws. The data on nutrient disappearance were ®tted exponentially to
estimate quick- (a), slow (b) and predicted (P0.025) degradable fractions and degradation rate (c) for
b. NDF and hemicellulose were reduced in treated compared with untreated straw (p < 0.001).
Disappearance of nutrients from treated straws was signi®cantly greater than that from untreated
straw at almost all incubations (p < 0.001). The a, b, c and P0.025 estimates were signi®cantly
increased by all treatments (p < 0.001). AHP treatment increased straw degradation more than
NaOH and CaO treatments. Although, CaO improved rumen degradation less than NaOH, its use to
increase straw digestion even moderately may be more desirable because it is readily available,
cheap and less dangerous for the users and the environment. # 2000 Published by Elsevier Science
B.V. All rights reserved.
Keywords: Rumen degradation; Straw; Calcium oxide; Sodium hydroxide; Hydrogen peroxide
*
Tel.: 44-1912226869; fax: 44-1912227811.
E-mail address: a.s.chaudhry@newcastle.ac.uk (A.S. Chaudhry).
0377-8401/00/$ ± see front matter # 2000 Published by Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 1 3 4 - 0
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
1. Introduction
Rumen degradation is critical in the utilization of cereal straws by ruminant animals.
However, using straws as an energy feed for ruminants is limited because their cell walls
contain three dimensional structures that are less available for microbial degradation in
the rumen (Wilkie, 1979; Sundstol and Owen, 1984; Chaudhry, 1998a). Consequently,
major nutrients from straws escape digestion and are wasted as faeces by the ruminants.
However, the energy value of straws can be increased if their cell wall structure is
modi®ed. Chemical treatments can modify cell wall to increase microbial degradation
and thus utilization of straws by ruminants (Jung et al., 1993).
Recently, Chaudhry (1997) following reports from Gould (1984) and Kerley et al.
(1986) con®rmed the effectiveness of alkaline hydrogen peroxide (NaOH H2O2, AHP)
to modify cell wall composition and in vitro dry matter digestibility (DMD) of wheat
straw. However, the need for a high amount (13 or 26 l kgÿ1 DM) of water and NaOH to
maintain the pH of AHP around 11.5 was considered a limitation for the on-farm
application of AHP. In another series of in vitro experiments, although the amount of
water was reduced, the use of calcium oxide (CaO) as an alternative alkali to maintain the
ef®cacy of AHP treatment even at a pH of 11.5 did not succeed (Chaudhry, 1998b). In
contrast, CaO alone increased the in vitro DMD of wheat straw under speci®c conditions.
In another study, Chaudhry (1998c) supported the ef®cacy of CaO and NaOH alone and
AHP in improving composition, nutrient digestion and fermentation of straw-based diets
in sheep. The increased digestion was perhaps due to the increased rate and extent of
straw degradation by rumen microbes. However, this assumption can only be
substantiated if the rumen degradation kinetics were studied. Moreover, as Chaudhry
(1998c) fed each straw together with a concentrate to sheep, it was not clear whether the
increased digestion was solely a consequence of a chemical treatment or was partly due to
its interaction with the concentrate.
Since rumen is the primary site of digestion for ®brous feeds in ruminants, it is
important to monitor degradation kinetics in response to modi®cation of cell wall caused
by alkali treatments. This may be achieved by using in sacco technique which is quicker
and cheaper than whole animal studies. Therefore, this study examined the effect of CaO,
NaOH and AHP on the rate and extent of degradation in sacco of wheat straw in sheep.
Treatment with CaO was tested as a cheap and a safe alternative to NaOH in improving
the rate and extent of straw degradation whereas NaOH also served as a control for AHP.
2. Materials and methods
2.1. Chemicals, straw and treatments
NaOH (32% w/w, speci®c gravity 1.35) and H2O2 (27.5% w/w, speci®c gravity 1.1) as
solutions and CaO as a ®ne powder were purchased from, respectively, Ellis and
Everrard, and BDH, UK and used to treat wheat straw variety Norman (straw, chopped
through an 8 mm sieve) as described by Chaudhry (1998c). Each treatment was applied
on kgÿ1 straw DM basis as described below:
A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
315
2.1.1. Control
Untreated straw served as a control.
2.1.2. CaO
The straw was mixed with 2 l of water in a mixer, dusted with 160 g CaO and the
contents were then re-mixed for ca. 1 h. The treated straw was then placed into a plastic
bag, tied up and stored at ca. 128C. The added amount of CaO was 160 g kgÿ1 straw DM
with a liquid : straw ratio of 2 : 1 and an initial pH of >13.
2.1.3. NaOH
The straw was mixed with 3 l of solution containing 80 g NaOH for ca. 1 h, placed into
a plastic bag and stored as described above. The added amount of NaOH was 80 g kgÿ1
DM at a liquid : straw ratio of 3 : 1 with an initial pH of >12 during 1 h of mixing. The
NaOH-treated straw also served as a control for AHP-treated straw.
2.1.4. AHP
Another batch of NaOH-treated straw was prepared as described in Section 2.1.3. After
27 h pre-soaking, 480 ml of H2O2 solution containing 132 g H2O2 were added, mixed for
5 h and stored as described earlier. During mixing, the pH of treated straw was monitored
at 30-min intervals and was observed to remain around 11.5 0.2. The amounts of added
NaOH and H2O2 were 80 and 132 g kgÿ1 straw DM, respectively.
2.2. Preparation of straws for rumen incubation
After 14-days storage in an open shed (average temperature 128C), each kg DM of
each treated and untreated straw was separately mixed with 100 g molasses (Molaferm50; United Molasses) in line with that described by Chaudhry (1998c). No other reason
for adding molasses into straws is offered. As hot water was added into molasses to
facilitate mixing, the molasses DM was reduced from 65 to 55% and hence the added
molasses in straw on DM basis was 55 g kgÿ1. The straws were dried and ground through
a 4 mm sieve before in sacco rumen incubations.
2.3. Animals, housing and feeding
Two Suffolk Mule wether sheep weighing between 60 and 64 kg were used in this
experiment. The sheep were ®tted with rumen cannulae and housed individually on
concrete ¯oors covered with sand. Each sheep was adapted to a ®xed daily intake of 1 kg
dried grass cubes containing 160 g crude protein for 14 days before in sacco degradability
was examined.
2.4. Experimental design and chemical analysis
A split-unit design involved two sheep (blocks), seven incubation times (main units)
and four test straws (sub-units) to study in sacco degradability of untreated and treated
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
straws. Duplicate samples of ca. 2.5 g DM of each test straw were weighed into separate
nylon bags which were then tied up by a plastic string to a 16 cm long ¯exible
polypropylene tube and suspended in the rumen of each sheep for 6, 12, 24, 48, 72 and
96 h. Given the limited rumen capacity of sheep, the samples were incubated as groups so
that only one group of four straws in duplicate was incubated in the rumen at any given
time. Samples of 0 h representing water-soluble fraction (a) were prepared by washing
bags, in duplicate, containing test straws for 30 min in a domestic washing machine.
After removal from the rumen at each incubation time, the residues within bags were
washed, freeze dried, ground through a 1 mm sieve and analysed together with
unincubated samples for DM, organic matter (OM) and neutral detergent ®bre (NDF)
(Van Soest et al., 1991). Disappearance of nutrients from each straw was calculated by
difference between nutrient composition of the unwashed and unincubated dried sample
of that straw and its residue after each incubation time in the rumen. Disappearance was
assumed to be due to degradation in the rumen. Samples of unwashed and unincubated
straws were also analysed for acid-detergent ®bre (ADF) and acid-detergent lignin (ADL)
to estimate cellulose and hemicellulose contents for each straw by subtracting ADL from
ADF and ADF from NDF, respectively.
2.5. Calculations and statistical analysis
The data from in sacco studies were ®tted into the exponential model
{p ab(1 ÿ eÿct)} of érskov and McDonald (1979) by using the Maximum
Likelihood Programme to obtain estimates of a, b and c for each straw in each sheep.
Here, a represented water-soluble (or quickly degradable) and b insoluble (or slowlydegradable) fractions whereas c degradation rate of b and t the hours of incubation. While
apparent degradability was represented by a b (asymptote), predicted rumen
degradability (P0.025) for each straw was also calculated from an equation,
P a (bc/c k), where k was the rumen out¯ow rate at 0.025 per hour (h) for
animals fed at a slightly above maintenance level (AFRC, 1993). The estimates of a, b, c,
asymptote and P0.025 were statistically analysed by using ANOVA in GENSTAT to test
the effect of chemical treatments on cell wall composition and the rate and extent of in
sacco degradability of straw.
3. Results
3.1. Cell wall composition
Table 1 presents mean cell wall composition of untreated and treated straws together
with their standard errors of differences (SED). All treatments reduced NDF and
hemicellulose contents in straw compared with untreated straw (p < 0.001). However,
CaO reduced NDF content more than NaOH and AHP did (p < 0.001). In contrast,
cellulose content was increased by all treatments whereas lignin content was increased by
NaOH and AHP (p < 0.05) but decreased by CaO (p < 0.05).
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
Table 1
Cell wall composition (g kgÿ1 OM) of molassed untreated and treated straws
Composition
Neutral detergent ®bre
Cellulose
Hemicellulose
Lignin
Straw treatmentsa
Untreated
CaO
NaOH
AHP
SED
841
451
259
104
676 c
528 b
29 b
92 d
781 b
533 b
67 b
129 a
776
562
23
115
16
13
26
4
a
c
a
c
b
b
b
b
a
Untreated, CaO, NaOH and AHP were respectively, untreated, CaO-, NaOH- and alkaline hydrogen
peroxide (NaOH H2O2, AHP) treated wheat straw. After 14-days storage at 128C, molasses was added to each
straw at 55 g molasses DM kgÿ1 straw DM; neutral detergent ®bre represented total cell wall; means with
different superscripts in a same row were signi®cantly different.
3.2. Nutrient disappearance
Figs. 1±3 illustrate the patterns of DM, OM and NDF disappearance from each test
straw during rumen incubation for various times together with SED for each incubation
Fig. 1. Pattern of disappearance of dry matter (DM) from molassed wheat straw, untreated (Untr) or treated
respectively with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubation for various
times in sheep. The lines represent data being ®tted for each test straw according to the exponential model. The
standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 6, 29, 18, 14, 26, 19 and 5,
respectively.
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
Fig. 2. Pattern of disappearance of organic matter (OM) from molassed wheat straw, untreated (Untr) or treated
respectively, with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubations for
various times in sheep. The lines represent data being ®tted for each test straw according to the exponential
model. The standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 9, 25, 32, 15, 18, 21
and 16, respectively.
time. The disappearance of DM, OM and NDF was signi®cantly greater for treated
straws than for untreated straw at almost all incubation times (p < 0.001). The incubation
at 6 h was an exception where disappearance of NDF from CaO-treated straw was
not signi®cantly greater than that of untreated straw. However, the loss of NDF from CaOtreated straw on washing with water was less than untreated straw (p < 0.001). In
contrast, the losses of DM and OM from treated straws on washing with water (0 h)
were greater than that from untreated straw. Signi®cant differences between treatments
for the disappearance of DM, OM and NDF during each incubation time were also
observed (p < 0.001). AHP treatment caused the greatest disappearance of DM, OM and
NDF from straws followed by NaOH and CaO. Untreated straw showed increased
disappearance of DM, OM and NDF with increasing incubation time to 96 h (p < 0.001).
In contrast, the disappearance of nutrients from NaOH and AHP straws almost peaked at
48 h whereas the disappearance from CaO straw continued to increase to 72 h
(p < 0.001).
A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
319
Fig. 3. Pattern of disappearance of neutral detergent ®bre (NDF) from molassed wheat straw, untreated (Untr) or
treated, respectively with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubation for
various times in sheep. The lines represent data being ®tted for each test straw according to the exponential
model. The standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 7, 35, 31, 15, 20, 26
and 7, respectively.
3.3. Degradation characteristics
Table 2 presents estimates of a, b, a b, c and P0.025 for untreated and treated
straws.
3.3.1. Quickly (a) and slowly degradable (b) fractions
Quickly- and slowly-degradable fractions for DM, OM and NDF were signi®cantly
affected by treatments (p < 0.001). Quickly degradable fractions of DM, OM and NDF
were greatest for AHP treated straw compared with untreated or other treated straws
(p < 0.001). In contrast, the slowly degradable fractions of DM and NDF and OM were
greatest respectively for CaO- and NaOH-treated straws. However, the quickly
degradable fraction of NDF in untreated straw was greater compared with NaOH- and
CaO-treated straws (p < 0.01) but was less in all straws compared with AHP-treated straw
(p < 0.01).
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
Table 2
Degradable fractions of nutrients (g kgÿ1) in molassed untreated, CaO-, NaOH- and AHP-treated wheat straws
after in sacco rumen incubations in sheep (Means with standard error of difference, SED)a
Parameters
Untreated
CaO
NaOH
AHP
SED
Dry matter
a
b
c (per hour)
ab
Pat 0.025
108
433
0.015
541
274
279
644
0.021
923
573
278
599
0.049
877
675
383
559
0.054
942
765
4.6
15
0.002
18
8
Organic matter
a
b
c (per hour)
ab
P0.025
113
444
0.014
557
272
199
643
0.034
842
570
189
674
0.049
863
635
290
644
0.051
934
722
9
20
0.002
20
10
Neutral detergent ®bre
a
b
c (per hour)
ab
P0.025
65
493
0.012
558
225
ÿ34
842
0.036
808
463
23
822
0.048
845
563
111
811
0.054
922
665
10
95
0.005
89
26
a
AHP, alkaline hydrogen peroxide (NaOH H2O2); a and b respectively, quickly and slowly degradable
fractions; c, degradation rate of b; a b and P0.025 represent apparent (asymptote) and predicted extent of
degradation, respectively.
3.3.2. Degradation rate (c) and predicted degradability (P0.025)
The degradation rates of DM, OM and NDF were signi®cantly faster for treated
compared with untreated straw (p < 0.001). However, AHP treatment increased
degradation rates most compared with NaOH and CaO. Predicted degradability of DM,
OM and NDF was signi®cantly greater for treated compared with untreated straw
(p < 0.001). However, predicted degradability was greatest for AHP (p < 0.001)
compared with NaOH and CaO.
4. Discussion
Following previous studies (Chaudhry, 1998b, c), this study examined the effects of
already determined best levels of CaO, NaOH and AHP treatments on rumen degradation
in sacco in sheep. While treatments modi®ed cell wall composition and increased in
sacco rumen degradation of straw compared with untreated straw, the extent of increase
depended on the type of chemical used. The reasons for those differences between
treatments are discussed by comparing the results with published information.
The reduction in NDF by different treatments was mainly due to the decreased
hemicellulose content of straw (Table 1). The chemical treatments may have removed
some linkages within hemicelluloses and thus enhanced their solubility in detergent
A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
321
solutions (Wilkie, 1979; Chaudhry, 1998a, c). The modi®ed cell wall composition of
straw in response to NaOH and AHP was comparable to that of Chaudhry (1997, 1998c)
for the same levels of those chemicals. However, the absolute NDF in untreated and
NaOH and AHP-treated straws of this study were greater than those of Chaudhry (1997).
The variation in NDF was perhaps due to the use of different straw variety and method by
Chaudhry (1997).
The ranking of untreated and treated straws based on an increased in sacco degradation
was comparable to those of in vitro (Chaudhry, 1998b) and in vivo (Chaudhry, 1998c)
digestibility of straw treated with the same chemicals. However, the absolute degradation
for various straws differed with the change in chemicals and incubation times. The NDF
disappearance from straws was relatively less than those of DM and OM during all
incubation times. The difference between losses of different nutrients was larger during
the initial 12 h of incubation. The NDF loss from untreated straw (368 g kgÿ1) after
rumen incubation of 96 h was less than that (500 g kgÿ1) of Miller and Oddoye (1989) for
the same incubation time. The degradation rate (c, 0.012) for NDF was also slower than
that (0.042) of the same researchers. The difference may be attributed to the difference in
straw variety (Huntingdon and Givens, 1995), particle size (Hovell et al., 1987), and
rumen conditions and diet composition of the host animal (Ramanzin et al., 1997). In
general, the degradation pattern for untreated and NaOH and AHP-treated straws of this
experiment agreed with published studies (Bharghava et al., 1989; Adebowale et al.,
1989). The nutrient disappearance from CaO-treated straw was reasonably close to that
from NaOH-treated straw at 72 h of incubation and thereafter. However, the degradation
pattern of CaO of this study cannot be compared with that in the literature because almost
no published information on the degradation pattern of CaO-treated straws could be
found.
The a b value (541 g kgÿ1) for DM in untreated straw of this study was comparable
to that (599 g kgÿ1) reported by Adebowale et al. (1989). The a b value for DM in CaO
was greater compared with NaOH. This represented the greater washing loss in water of
residual CaO from straw simply because more CaO than NaOH was initially used to treat
the straw. However, it is noted that this variation was not caused by the washing loss of
added molasses since the same amounts of molasses were added across treatments. The
a b values of OM and NDF for CaO and NaOH were closer to each other despite
signi®cantly different degradation rates (c values, 0.034 vs. 0.049 for OM; and 0.036 vs.
0.048 for NDF). The non-signi®cant difference between CaO and NaOH for the apparent
extent of degradation (a b or asymptote) in this study, was comparable to that of in vitro
digestibility (Chaudhry, 1998b) but was contrary to the in vivo digestibility (Chaudhry,
1998c) where NaOH was better than CaO. However, when degradation (c) and rumen
out¯ow rates (k) were taken into consideration, the differences between the predicted
degradability (P0.025) of different straws were comparable to those of in vivo digestibility
(Chaudhry, 1998c). The decreased losses of DM and OM from untreated and DM from
CaO at 6 h were perhaps due to the particle-associated microbes that increased residual
weights of straw during incubation.
AHP was the most effective treatment in improving degradation of wheat straw. The
results agreed with the previous reports where AHP was better than its NaOH-control and
CaO in improving in vitro and in vivo digestibility of wheat straw (Chaudhry, 1997,
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A.S. Chaudhry / Animal Feed Science and Technology 83 (2000) 313±323
1998b, c). Although CaO greatly reduced NDF and lignin of straw, it did not improve
rumen degradation as much as NaOH and AHP did. It may be due to the greater effect of
CaO on the lignin molecule (Table 1) to release phenolics to inhibit rumen microbes and
consequently rumen degradation of straw (Marvin et al., 1996). In contrast, Silanikove
(1994) reported a greater deligni®cation in cotton straw when NaOH instead of CaO was
used as an alkali in AHP treatment. However, no difference was reported between the two
chemicals for in vitro digestibility of cotton straw. Chaudhry (1998a, b, c), has discussed
the potential and problems associated with chemical treatments in improving nutritive
value of cereal straws. In summary, the study supported the hypothesis that the increased
digestion of cereal straws by ruminants was a consequence of increased rate and extent of
their rumen degradation.
In conclusion, CaO modi®ed cell wall composition and increased rumen degradation in
sacco of wheat straw and therefore could be used as an alternative to NaOH to increase
the digestible OM intake of sheep fed treated straw. Although CaO improved rumen
degradation less than NaOH did, its use to increase straw digestion even moderately may
be more desirable because it is readily available, cheap and less dangerous for the users
and the environment. However, it is essential to reduce the level of chemicals but without
reducing their effect to improve straw digestion in ruminants. It is also essential to
perform a cost-bene®t analysis before applying treatment on-farm to improve low quality
forages. The bene®ts of using chemical treatments would be determined by the
availability and price of other animal feeds in different regions of the world at a particular
time.
Acknowledgements
ASC thanks Dr. E.L. Miller for his invaluable advice and comments during studies at
the University of Cambridge, UK and Mr. Allan Lisle from the University of Queensland
at Gatton, Australia for his statistical advice.
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