Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol83.Issue1.Jan2000:
Animal Feed Science and Technology
83 (2000) 57±65
Nutritional properties of the leaf
and stem of rice straw
J. Vadiveloo*
Faculty of Applied Sciences, MARA University of Technology, 40450 Shah Alam, Malaysia
Received 13 January 1999; received in revised form 26 July 1999; accepted 14 September 1999
Abstract
The proportion of the leaf blade, leaf sheath and stem fractions in six rice straw varieties
averaged 30, 40 and 30%, respectively. In vitro dry matter digestibility (IVD) of these fractions,
estimated by the cellulase-neutral detergent solution procedure, was 503, 513 and 610 g/kg,
respectively. The lower IVD of the blade and sheath was due to lower degradation parameters
estimated by a simple technique of incubating samples in a cellulase-buffer solution at 388C for 3,
6, 12, 24, 48 and 72 h. Treatment with 4% urea solution for 21 days increased the IVD and the
degradation characteristics of the leaf fraction more than the stem but treatment with a 4% sodium
hydroxide (NaOH) solution for 21 days improved the IVD and degradability characteristics of all
straw fractions to the same extent.
The leaf had a lower neutral detergent fibre (NDF), higher total and insoluble ash than the stem.
Urea treatment which increased total ash but decreased insoluble ash in the leaf were increased in
the stem. NaOH treatment increased total and insoluble ash in all fractions. The NDF content, lower
in the untreated leaf compared to the stem, was unaffected by but decreased after urea and NaOH
treatment, respectively. Crude protein (CP) content, similar between untreated straw fractions,
increased after urea but decreased after NaOH treatment .Principal component scores of the leaf and
stem fractions derived from a principal component analysis of the analysed variables showed that
the leaf ranked higher in nutritive value than the stem before and after chemical treatment. The high
leaf content of modern rice straw varieties should therefore promote the utilisation of rice straw as a
ruminant feed. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Nutritional value; Leaf; Stem; Rice straw
*
Tel.: 60-35564330; fax: 60-35597681.
E-mail address: [email protected] (J. Vadiveloo).
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 1 0 7 - 8
58
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
1. Introduction
The most widely used measure of the nutritive value of a feed is its digestibility. The
digestibility of the leaf of rice straw determined in vivo (Phang and Vadiveloo, 1992), in
sacco (Walli et al., 1988; Nakashima and Orskov, 1990) and in vitro (Bainton et al., 1991;
Vadiveloo, 1992) is characteristically lower than the stem. As leaf comprises some 70%
of whole straw (Vadiveloo, 1995), low leaf digestibility reduces the overall quality of rice
straw and limits its use as an animal feed. Strategies to improve feeding value, such as
varietal selection (Capper, 1988; Vadiveloo, 1995) and chemical treatment (Tuen et al.,
1991; Mgheni et al., 1993; Vadiveloo, 1996) have consequently focussed on securing
improvements in digestibility.
Although digestibility is important, it is not the sole determinant of the nutritive value
of a feed (Vadiveloo and Fadel, 1992). With low quality feeds, feed intake and
compositional characteristics are also important (Madsen et al., 1997). An objective of
the present study was therefore to compare the nutritive value of leaf and stem based on
several measures of nutritive value. This assessment was made before and after chemical
treatment as chemical treatment still remains a popular method of upgrading rice straw
(Tuen et al., 1991; Mgheni et al., 1993; Vadiveloo, 1996).
Quantitative estimates of the degradation of a feed provide important information on
fermentation characteristics and improve our understanding of feed utilisation. Studies on
degradation kinetics have been conventionally carried out using the nylon bag (Mehrez
and Orskov, 1977) or the in vitro gas production technique (Menke and Steingass, 1988;
Blummel and Orskov, 1993). Both techniques require fistulated animals and a high
degree of standardisation. The use of a prepared cellulase solution, which avoids these
problems, has been employed to study the degradation kinetics of hays (Lopez et al.,
1998). However, there are no reports in the literature of using an enzymatic procedure to
determine the degradation kinetics of rice straw. In this study, a cellulase-buffer solution
was used to compare the degradation of the leaf and stem fractions before and after
chemical treatment.
2. Materials and methods
2.1. Rice straw
Six straw varieties, MR 84, MR 151, MR 162, MR 164, MR 166 and MR 167 handharvested at maturity 12 cm above the ground in June 1994 from the Tanjung Karang
district of Selangor were field-dried. The relative proportion by weight of leaf blade, leaf
sheath and stem (including inflorescence) in approximately 500 g of whole straw was
estimated in triplicate for each variety. Straw fractions were ground to pass through a
1 mm sieve and the ground fractions hand-mixed (using a glass rod) with 4% urea or 4%
sodium hydroxide (NaOH) solution in the ratio of 50 g straw to 200 ml of solution (equal
to 160 g chemical/kg straw in 4000 ml of water). The treated samples were kept in screwtop plastic jars at room temperature for 21 days after which they were oven-dried at 608C
to constant weight.
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
59
2.2. Chemical composition and degradability
Treated and untreated samples were analysed for total ash, crude protein (AOAC,
1984), neutral detergent fibre (NDF) and ash insoluble in neutral detergent solution (Van
Soest et al., 1991). In vitro dry matter digestibility (IVD) was estimated by the cellulaseneutral detergent solution procedure of Bughrara and Sleper (1986) using the Onozuka 3S
enzyme (Yakult Biochemicals).Treated and untreated straw fractions of weight 0.5 g were
incubated in cellulase-buffer solution for 3, 6, 12, 24, 48 and 72 h at 388C. After
incubation, the residues were washed with water, oven-dried at 1008C and weighed. Time
of incubation on the cellulase digestion of the straw fractions was compared by an
analysis of variance. Degradation characteristics were described by the exponential
equation p a b(1 ± eÿct) where p is degradation at time t(h) and a, b and c are
constants (Orskov and McDonald, 1979). Constants a, b and c represent the rapidly
degradable fraction, slowly degradable fraction and fractional degradation rate,
respectively.
2.3. Statistical analyses
Differences between straw fractions in chemical composition, IVD and degradation
kinetics before and after chemical treatment were compared by an analysis of variance.
Principal component analysis of the data on NDF, total ash, insoluble ash, IVD and CP
was carried out with the following objectives:
(a) To quantify the contribution of each variable to the variation in nutritive value
between the straw fractions. The sign and magnitude of the eigenvectors (linear
combinations of the original variables) were examined for their relevance in explaining
the nutritive values of the straw fractions, negative signs for NDF, total ash and insoluble
ash contributing negatively, and positive signs for IVD and CP contributing positively, to
nutritive value.
(b) To compute a single variable (principal component score) for each straw fraction
that best summarised all the original variables. The principal component scores were
standardised to unit variance and were used to rank the nutritive value of the straw
fractions (Vadiveloo, 1995). Principal component analysis is a multivariate statistical
procedure which allows several criterion variables to be used simultaneously in
evaluating mean differences. Statistical analyses were run on a SAS Version 6 statistical
package (Statistical Analysis Systems Institute Inc., 1987).
3. Results
The mean proportion of the straw fractions in the six varieties, their chemical
composition and IVD before and after chemical treatment are shown in Table 1.
Untreated leaf blade and leaf sheath were lower than stem in IVD and NDF but higher in
ash content. The CP contents were similar. Urea treatment markedly increased the IVD of
the leaf blade and leaf sheath but did not alter the IVD of the stem. NDF values were not
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J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Table 1
Proportion (% in whole straw), chemical composition (g/kg DM) and in vitro dry matter digestibility (IVD,
g/kg DM) of untreated and chemically-treated straw fractionsa
Fraction
Proportion
(sd)
Treatment
Total ash
NDF
Insoluble
ash
IVD
Crude
protein
Leaf blade
31.1
(2.10)
Leaf sheath
40.3
(1.70)
Stem
27.8
(1.40)
Untreated
Urea
NaOH
Untreated
Urea
NaOH
Untreated
Urea
NaOH
SE diff.
185
192
234
191
218
250
140
155
187
3.0***
581
584
522
644
634
554
681
676
593
5.3***
64
63
71
59
57
80
22
32
28
2.5***
503
704
823
513
576
821
610
610
863
8.1***
46
62
36
29
40
28
35
46
29
1.9***
a
*** ± P < 0.001.
affected but insoluble ash contents were reduced. The CP was increased for all fractions
following urea treatment. NaOH treatment increased the IVD and ash content, reduced
NDF and CP for all fractions. Varietal differences in the composition and IVD of straw
fractions were small and hence are not reported.
Statistics from the principal component analysis of the straw fractions are shown in
Table 2. An examination of the eigenvectors for the first principal component for
untreated and NaOH-treated straw showed that the sign and magnitude for total ash and
NDF, insoluble ash and IVD were of the same magnitude but of opposite signs.
Numerically therefore only the positive eigenvector for CP would make a net contribution
to the component scores which effectively represented differences between straw
fractions in their CP content. Leaf blade with the highest positive score was thus ranked
first and stem with the highest negative score was ranked third (Table 2). Eigenvectors
with negative signs for total ash, NDF and insoluble ash and positive signs for IVD and
CP were found in the second principal component for untreated and NaOH treated straw.
High positive scores associated with these components would mean high nutritive value
Table 2
Variance (%), eigenvectors, scores and ranks on the first and second principal components (PC)
Treatment PC %
Eigenvectors
Total
ash
Untreated
Urea
NaOH
1
2
1
2
1
2
Scores
NDF Insoluble IVD
ash
77
0.47 ÿ0.47 0.50
23 ÿ0.36 ÿ0.34 ÿ0.17
65
0.24 ÿ0.55 0.48
35
0.68 ÿ0.09 0.37
78
0.47 ÿ0.48 0.49
22 ÿ0.34 ÿ0.33 ÿ0.26
CP
Blade
Rank
Sheath Stem
ÿ0.50 0.23 0.84
0.26
0.19 0.83 0.79 ÿ1.12
0.45 0.45 1.08 ÿ0.20
ÿ0.44 ÿ0.44 ÿ0.40
1.14
ÿ0.50 0.25 0.69
0.46
0.15 0.83 0.93 ÿ1.06
ÿ1.11
0.33
ÿ0.89
ÿ0.74
ÿ1.15
0.14
1
2
3
blade
blade
blade
sheath
blade
blade
sheath
stem
sheath
blade
sheath
stem
stem
sheath
stem
stem
stem
sheath
61
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Table 3
Mean effect of time of incubation (h) on the cellulase degradation (% in DM) of straw fractions before and after
chemical treatmenta
Fraction
Leaf blade
Leaf sheath
Stem
a
Treatment
Untreated
Urea
NaOH
Untreated
Urea
NaOH
Untreated
Urea
NaOH
SE diff.
Time of incubation (h)
3
6
12
24
48
72
15.3
18.0
37.9
19.4
19.2
40.6
27.2
24.5
46.4
0.53***
17.8
24.7
46.6
22.9
26.2
45.8
32.7
30.2
52.3
1.05***
19.8
30.6
53.3
25.5
29.9
54.5
36.6
34.3
61.8
0.72***
26.1
40.3
58.2
32.5
35.9
59.6
44.4
41.4
72.0
0.88***
25.1
44.3
65.6
31.3
38.3
69.1
43.3
43.4
79.9
0.82***
28.4
42.7
65.4
33.7
37.5
69.7
45.6
44.5
80.5
0.96***
*** ± P < 0.001.
and high negative scores, poor nutritive value. For both these components leaf blade
was ranked highest in nutritive value. The sign and magnitude of the eigenvectors on
the first component of urea treated straw showed that the component scores were
influenced by the net positive loading on IVD and CP. Thus, the main effect of urea
treatment was to increase the IVD and CP of the straw fractions; the component scores
indicate that this increase was in the order blade > sheath > stem. The magnitude of the
eigenvector for NDF on the second component for urea treated straw was small and can
be ignored. The positive score for leaf sheath indicates that urea treatment had a greater
effect on its ash values (positive eigenvectors) than on the ash values of the stem fraction
(negative score).
The mean effect of time of incubation on the cellulase degradation of straw fractions
before and after chemical treatment are shown in Table 3 and Fig. 1. Treatment effects
were significant (P < 0.001) for all incubation times and except for urea-treated stem,
were in the order NaOH > urea > untreated. Degradation of all fractions increased
cumulatively with time for all treatments.
Mean degradation characteristics of straw fractions before and after chemical treatment
are shown in Table 4. Degradation characteristics (constants a, b and c) for untreated
straw fractions were in the order stem > sheath > blade. Urea treatment decreased but
NaOH treatment increased the rapidly degradable fraction of blade, stem and sheath.
Urea treatment increased the slowly degradable fractions in the order blade > sheath >
stem but the increase was the same for all fractions after NaOH treatment. Consequently
the increase in potential degradability (constants a b) for urea-treated straw was in the
order blade > sheath > stem, the reverse of untreated straw. The NaOH treatment affected
similar increases in the slowly degradable fractions of leaf and stem. Degradation rate
was significantly reduced by urea and NaOH treatment for stem and for NaOH treatment
only for leaf sheath. The degradation rate for leaf blade increased after urea and NaOH
treatment but was not significant (P > 0.05).
62
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Fig. 1. Cellulase degradation (% in DM) of straw fractions (control ^; urea &, NaOH ~).
Table 4
Degradation characteristics of the straw fractions before and after chemical treatmenta
Fraction
Leaf blade
Leaf sheath
Stem
a
Treatment
Untreated
Urea
NaOH
SE diff.
Untreated
Urea
NaOH
SE diff.
Untreated
Urea
NaOH
SE diff.
*** ± P < 0.001; ns ± P > 0.05.
Constants
ÿ1
a (%)
b (%)
c (h )
12.4
10.7
32.2
0.88***
15.4
13.2
35.6
0.83***
21.0
19.3
38.9
1.17***
15.8
33.1
33.2
0.87***
17.8
24.7
35.0
1.32***
24.0
25.0
42.5
1.09***
0.0657
0.0849
0.0795
0.01048ns
0.0853
0.1061
0.0574
0.00695***
0.1033
0.0841
0.0647
0.00071***
Asymptote
a b (%)
RSD
27.6
43.8
65.0
1.02***
33.1
37.9
68.9
1.05***
44.6
44.3
81.3
1.39***
2.26
1.61
1.73
1.55
1.70
2.84
2.10
2.12
2.27
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
63
4. Discussion
The IVD of the untreated straw fractions estimated by the cellulase-neutral detergent
solution procedure ranged from 50% for leaf blade to 61% for stem (Table 1), similar to
earlier results with 32 straw varieties (Vadiveloo, 1995) and in sacco results by Shen et al.
(1998b). These data are also comparable to the dry matter digestibility of 57% and 69%
obtained with supplemented rice straw leaf and stem diets fed to goats, respectively
(Phang and Vadiveloo, 1992).
The lower IVD of the leaf compared to that of stem is in agreement with Malaysian
(Vadiveloo, 1992, 1995) and other studies (Shen et al., 1998b; Nakashima and Orskov,
1990; Bainton et al., 1991). This was ascribed to lower values for all degradation
parameters (Table 4). Urea treatment increased the IVD of leaf blade and leaf sheath
through increases in the proportion of their slowly degradable fractions. Hence, only the
leaf fraction recorded an improvement in potential degradability. These results obtained
by a simpler cellulase technique, are corroborated by Nakashima and Orskov (1990)
using the nylon bag technique on ammonia-treated rice straw and Shen et al. (1998b)
using the nylon bag and in vitro gas production techniques on urea-treated straw. It is
interesting that with barley straw, the results are reversed ± untreated leaf is more
degradable than stem but is less improved by ammonia treatment (Ramanzin et al., 1986).
Urea treatment reduced the insoluble ash content of the leaf fraction probably by an
increased extraction of biogenic silica (Shen et al., 1998a). Urea treatment may also
weaken the bonds between the silica-covered cuticle and underlying tissues (Bae et al.,
1997) thus removing an important barrier to digestion and exposing the underlying silicafree tissues to enzymatic action.
The NaOH treatment increased the IVD of both leaf and stem fractions by increasing
their rapidly and slowly degradable fractions. In contrast to urea treatment, the magnitude
of the increase was similar for all straw fractions. Given the absence of similar studies
in the literature, more studies need to be carried out to corroborate these findings. The
enhanced degradability has been ascribed to a solubilisation of total phenolics
(Chesson, 1981), arabinoxylans and cellulose (Lindberg et al., 1984) arising from the
cleavage of alkali-labile lignin-carbohydrate linkages (Alexander et al., 1987; Ternrud
et al., 1988).
Apart from IVD, the leaf and stem also differed in total ash, insoluble ash and
NDF contents. Principal components analysis was therefore used to evaluate the
relative nutritional value of the leaf and stem fractions by accounting for all parameters
instead of only digestibility. Principal components analysis is a versatile though
exploratory technique which has been used to rank straw varieties (Vadiveloo, 1995),
interpret near infra-red spectroscopic data (Bertrand et al., 1987; Grant et al., 1988) and
characterise analytical data (Martin-Alvarez et al., 1988; Martin-Alvarez and Herranz,
1991).
Principal components analysis ranked the leaf fraction higher in nutritive value than the
stem before and after chemical treatment. The practical value of this result is that the
increasingly high leaf content of modern rice straw varieties arising from breeding for
higher grain yield and quality should provide an impetus for the utilisation of rice straw
as a ruminant feed.
64
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Acknowledgements
Technical assistance by Nik Nazri Nik Yusof, Ku Aishah Ku Din and Astifarini Buang
is recorded with thanks. Financial assistance was provided by MARA University of
Technology. Rice straw was provided by the Malaysian Agricultural Research and
Development Institute, Tanjung Karang.
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83 (2000) 57±65
Nutritional properties of the leaf
and stem of rice straw
J. Vadiveloo*
Faculty of Applied Sciences, MARA University of Technology, 40450 Shah Alam, Malaysia
Received 13 January 1999; received in revised form 26 July 1999; accepted 14 September 1999
Abstract
The proportion of the leaf blade, leaf sheath and stem fractions in six rice straw varieties
averaged 30, 40 and 30%, respectively. In vitro dry matter digestibility (IVD) of these fractions,
estimated by the cellulase-neutral detergent solution procedure, was 503, 513 and 610 g/kg,
respectively. The lower IVD of the blade and sheath was due to lower degradation parameters
estimated by a simple technique of incubating samples in a cellulase-buffer solution at 388C for 3,
6, 12, 24, 48 and 72 h. Treatment with 4% urea solution for 21 days increased the IVD and the
degradation characteristics of the leaf fraction more than the stem but treatment with a 4% sodium
hydroxide (NaOH) solution for 21 days improved the IVD and degradability characteristics of all
straw fractions to the same extent.
The leaf had a lower neutral detergent fibre (NDF), higher total and insoluble ash than the stem.
Urea treatment which increased total ash but decreased insoluble ash in the leaf were increased in
the stem. NaOH treatment increased total and insoluble ash in all fractions. The NDF content, lower
in the untreated leaf compared to the stem, was unaffected by but decreased after urea and NaOH
treatment, respectively. Crude protein (CP) content, similar between untreated straw fractions,
increased after urea but decreased after NaOH treatment .Principal component scores of the leaf and
stem fractions derived from a principal component analysis of the analysed variables showed that
the leaf ranked higher in nutritive value than the stem before and after chemical treatment. The high
leaf content of modern rice straw varieties should therefore promote the utilisation of rice straw as a
ruminant feed. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Nutritional value; Leaf; Stem; Rice straw
*
Tel.: 60-35564330; fax: 60-35597681.
E-mail address: [email protected] (J. Vadiveloo).
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 1 0 7 - 8
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1. Introduction
The most widely used measure of the nutritive value of a feed is its digestibility. The
digestibility of the leaf of rice straw determined in vivo (Phang and Vadiveloo, 1992), in
sacco (Walli et al., 1988; Nakashima and Orskov, 1990) and in vitro (Bainton et al., 1991;
Vadiveloo, 1992) is characteristically lower than the stem. As leaf comprises some 70%
of whole straw (Vadiveloo, 1995), low leaf digestibility reduces the overall quality of rice
straw and limits its use as an animal feed. Strategies to improve feeding value, such as
varietal selection (Capper, 1988; Vadiveloo, 1995) and chemical treatment (Tuen et al.,
1991; Mgheni et al., 1993; Vadiveloo, 1996) have consequently focussed on securing
improvements in digestibility.
Although digestibility is important, it is not the sole determinant of the nutritive value
of a feed (Vadiveloo and Fadel, 1992). With low quality feeds, feed intake and
compositional characteristics are also important (Madsen et al., 1997). An objective of
the present study was therefore to compare the nutritive value of leaf and stem based on
several measures of nutritive value. This assessment was made before and after chemical
treatment as chemical treatment still remains a popular method of upgrading rice straw
(Tuen et al., 1991; Mgheni et al., 1993; Vadiveloo, 1996).
Quantitative estimates of the degradation of a feed provide important information on
fermentation characteristics and improve our understanding of feed utilisation. Studies on
degradation kinetics have been conventionally carried out using the nylon bag (Mehrez
and Orskov, 1977) or the in vitro gas production technique (Menke and Steingass, 1988;
Blummel and Orskov, 1993). Both techniques require fistulated animals and a high
degree of standardisation. The use of a prepared cellulase solution, which avoids these
problems, has been employed to study the degradation kinetics of hays (Lopez et al.,
1998). However, there are no reports in the literature of using an enzymatic procedure to
determine the degradation kinetics of rice straw. In this study, a cellulase-buffer solution
was used to compare the degradation of the leaf and stem fractions before and after
chemical treatment.
2. Materials and methods
2.1. Rice straw
Six straw varieties, MR 84, MR 151, MR 162, MR 164, MR 166 and MR 167 handharvested at maturity 12 cm above the ground in June 1994 from the Tanjung Karang
district of Selangor were field-dried. The relative proportion by weight of leaf blade, leaf
sheath and stem (including inflorescence) in approximately 500 g of whole straw was
estimated in triplicate for each variety. Straw fractions were ground to pass through a
1 mm sieve and the ground fractions hand-mixed (using a glass rod) with 4% urea or 4%
sodium hydroxide (NaOH) solution in the ratio of 50 g straw to 200 ml of solution (equal
to 160 g chemical/kg straw in 4000 ml of water). The treated samples were kept in screwtop plastic jars at room temperature for 21 days after which they were oven-dried at 608C
to constant weight.
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
59
2.2. Chemical composition and degradability
Treated and untreated samples were analysed for total ash, crude protein (AOAC,
1984), neutral detergent fibre (NDF) and ash insoluble in neutral detergent solution (Van
Soest et al., 1991). In vitro dry matter digestibility (IVD) was estimated by the cellulaseneutral detergent solution procedure of Bughrara and Sleper (1986) using the Onozuka 3S
enzyme (Yakult Biochemicals).Treated and untreated straw fractions of weight 0.5 g were
incubated in cellulase-buffer solution for 3, 6, 12, 24, 48 and 72 h at 388C. After
incubation, the residues were washed with water, oven-dried at 1008C and weighed. Time
of incubation on the cellulase digestion of the straw fractions was compared by an
analysis of variance. Degradation characteristics were described by the exponential
equation p a b(1 ± eÿct) where p is degradation at time t(h) and a, b and c are
constants (Orskov and McDonald, 1979). Constants a, b and c represent the rapidly
degradable fraction, slowly degradable fraction and fractional degradation rate,
respectively.
2.3. Statistical analyses
Differences between straw fractions in chemical composition, IVD and degradation
kinetics before and after chemical treatment were compared by an analysis of variance.
Principal component analysis of the data on NDF, total ash, insoluble ash, IVD and CP
was carried out with the following objectives:
(a) To quantify the contribution of each variable to the variation in nutritive value
between the straw fractions. The sign and magnitude of the eigenvectors (linear
combinations of the original variables) were examined for their relevance in explaining
the nutritive values of the straw fractions, negative signs for NDF, total ash and insoluble
ash contributing negatively, and positive signs for IVD and CP contributing positively, to
nutritive value.
(b) To compute a single variable (principal component score) for each straw fraction
that best summarised all the original variables. The principal component scores were
standardised to unit variance and were used to rank the nutritive value of the straw
fractions (Vadiveloo, 1995). Principal component analysis is a multivariate statistical
procedure which allows several criterion variables to be used simultaneously in
evaluating mean differences. Statistical analyses were run on a SAS Version 6 statistical
package (Statistical Analysis Systems Institute Inc., 1987).
3. Results
The mean proportion of the straw fractions in the six varieties, their chemical
composition and IVD before and after chemical treatment are shown in Table 1.
Untreated leaf blade and leaf sheath were lower than stem in IVD and NDF but higher in
ash content. The CP contents were similar. Urea treatment markedly increased the IVD of
the leaf blade and leaf sheath but did not alter the IVD of the stem. NDF values were not
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J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Table 1
Proportion (% in whole straw), chemical composition (g/kg DM) and in vitro dry matter digestibility (IVD,
g/kg DM) of untreated and chemically-treated straw fractionsa
Fraction
Proportion
(sd)
Treatment
Total ash
NDF
Insoluble
ash
IVD
Crude
protein
Leaf blade
31.1
(2.10)
Leaf sheath
40.3
(1.70)
Stem
27.8
(1.40)
Untreated
Urea
NaOH
Untreated
Urea
NaOH
Untreated
Urea
NaOH
SE diff.
185
192
234
191
218
250
140
155
187
3.0***
581
584
522
644
634
554
681
676
593
5.3***
64
63
71
59
57
80
22
32
28
2.5***
503
704
823
513
576
821
610
610
863
8.1***
46
62
36
29
40
28
35
46
29
1.9***
a
*** ± P < 0.001.
affected but insoluble ash contents were reduced. The CP was increased for all fractions
following urea treatment. NaOH treatment increased the IVD and ash content, reduced
NDF and CP for all fractions. Varietal differences in the composition and IVD of straw
fractions were small and hence are not reported.
Statistics from the principal component analysis of the straw fractions are shown in
Table 2. An examination of the eigenvectors for the first principal component for
untreated and NaOH-treated straw showed that the sign and magnitude for total ash and
NDF, insoluble ash and IVD were of the same magnitude but of opposite signs.
Numerically therefore only the positive eigenvector for CP would make a net contribution
to the component scores which effectively represented differences between straw
fractions in their CP content. Leaf blade with the highest positive score was thus ranked
first and stem with the highest negative score was ranked third (Table 2). Eigenvectors
with negative signs for total ash, NDF and insoluble ash and positive signs for IVD and
CP were found in the second principal component for untreated and NaOH treated straw.
High positive scores associated with these components would mean high nutritive value
Table 2
Variance (%), eigenvectors, scores and ranks on the first and second principal components (PC)
Treatment PC %
Eigenvectors
Total
ash
Untreated
Urea
NaOH
1
2
1
2
1
2
Scores
NDF Insoluble IVD
ash
77
0.47 ÿ0.47 0.50
23 ÿ0.36 ÿ0.34 ÿ0.17
65
0.24 ÿ0.55 0.48
35
0.68 ÿ0.09 0.37
78
0.47 ÿ0.48 0.49
22 ÿ0.34 ÿ0.33 ÿ0.26
CP
Blade
Rank
Sheath Stem
ÿ0.50 0.23 0.84
0.26
0.19 0.83 0.79 ÿ1.12
0.45 0.45 1.08 ÿ0.20
ÿ0.44 ÿ0.44 ÿ0.40
1.14
ÿ0.50 0.25 0.69
0.46
0.15 0.83 0.93 ÿ1.06
ÿ1.11
0.33
ÿ0.89
ÿ0.74
ÿ1.15
0.14
1
2
3
blade
blade
blade
sheath
blade
blade
sheath
stem
sheath
blade
sheath
stem
stem
sheath
stem
stem
stem
sheath
61
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Table 3
Mean effect of time of incubation (h) on the cellulase degradation (% in DM) of straw fractions before and after
chemical treatmenta
Fraction
Leaf blade
Leaf sheath
Stem
a
Treatment
Untreated
Urea
NaOH
Untreated
Urea
NaOH
Untreated
Urea
NaOH
SE diff.
Time of incubation (h)
3
6
12
24
48
72
15.3
18.0
37.9
19.4
19.2
40.6
27.2
24.5
46.4
0.53***
17.8
24.7
46.6
22.9
26.2
45.8
32.7
30.2
52.3
1.05***
19.8
30.6
53.3
25.5
29.9
54.5
36.6
34.3
61.8
0.72***
26.1
40.3
58.2
32.5
35.9
59.6
44.4
41.4
72.0
0.88***
25.1
44.3
65.6
31.3
38.3
69.1
43.3
43.4
79.9
0.82***
28.4
42.7
65.4
33.7
37.5
69.7
45.6
44.5
80.5
0.96***
*** ± P < 0.001.
and high negative scores, poor nutritive value. For both these components leaf blade
was ranked highest in nutritive value. The sign and magnitude of the eigenvectors on
the first component of urea treated straw showed that the component scores were
influenced by the net positive loading on IVD and CP. Thus, the main effect of urea
treatment was to increase the IVD and CP of the straw fractions; the component scores
indicate that this increase was in the order blade > sheath > stem. The magnitude of the
eigenvector for NDF on the second component for urea treated straw was small and can
be ignored. The positive score for leaf sheath indicates that urea treatment had a greater
effect on its ash values (positive eigenvectors) than on the ash values of the stem fraction
(negative score).
The mean effect of time of incubation on the cellulase degradation of straw fractions
before and after chemical treatment are shown in Table 3 and Fig. 1. Treatment effects
were significant (P < 0.001) for all incubation times and except for urea-treated stem,
were in the order NaOH > urea > untreated. Degradation of all fractions increased
cumulatively with time for all treatments.
Mean degradation characteristics of straw fractions before and after chemical treatment
are shown in Table 4. Degradation characteristics (constants a, b and c) for untreated
straw fractions were in the order stem > sheath > blade. Urea treatment decreased but
NaOH treatment increased the rapidly degradable fraction of blade, stem and sheath.
Urea treatment increased the slowly degradable fractions in the order blade > sheath >
stem but the increase was the same for all fractions after NaOH treatment. Consequently
the increase in potential degradability (constants a b) for urea-treated straw was in the
order blade > sheath > stem, the reverse of untreated straw. The NaOH treatment affected
similar increases in the slowly degradable fractions of leaf and stem. Degradation rate
was significantly reduced by urea and NaOH treatment for stem and for NaOH treatment
only for leaf sheath. The degradation rate for leaf blade increased after urea and NaOH
treatment but was not significant (P > 0.05).
62
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Fig. 1. Cellulase degradation (% in DM) of straw fractions (control ^; urea &, NaOH ~).
Table 4
Degradation characteristics of the straw fractions before and after chemical treatmenta
Fraction
Leaf blade
Leaf sheath
Stem
a
Treatment
Untreated
Urea
NaOH
SE diff.
Untreated
Urea
NaOH
SE diff.
Untreated
Urea
NaOH
SE diff.
*** ± P < 0.001; ns ± P > 0.05.
Constants
ÿ1
a (%)
b (%)
c (h )
12.4
10.7
32.2
0.88***
15.4
13.2
35.6
0.83***
21.0
19.3
38.9
1.17***
15.8
33.1
33.2
0.87***
17.8
24.7
35.0
1.32***
24.0
25.0
42.5
1.09***
0.0657
0.0849
0.0795
0.01048ns
0.0853
0.1061
0.0574
0.00695***
0.1033
0.0841
0.0647
0.00071***
Asymptote
a b (%)
RSD
27.6
43.8
65.0
1.02***
33.1
37.9
68.9
1.05***
44.6
44.3
81.3
1.39***
2.26
1.61
1.73
1.55
1.70
2.84
2.10
2.12
2.27
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
63
4. Discussion
The IVD of the untreated straw fractions estimated by the cellulase-neutral detergent
solution procedure ranged from 50% for leaf blade to 61% for stem (Table 1), similar to
earlier results with 32 straw varieties (Vadiveloo, 1995) and in sacco results by Shen et al.
(1998b). These data are also comparable to the dry matter digestibility of 57% and 69%
obtained with supplemented rice straw leaf and stem diets fed to goats, respectively
(Phang and Vadiveloo, 1992).
The lower IVD of the leaf compared to that of stem is in agreement with Malaysian
(Vadiveloo, 1992, 1995) and other studies (Shen et al., 1998b; Nakashima and Orskov,
1990; Bainton et al., 1991). This was ascribed to lower values for all degradation
parameters (Table 4). Urea treatment increased the IVD of leaf blade and leaf sheath
through increases in the proportion of their slowly degradable fractions. Hence, only the
leaf fraction recorded an improvement in potential degradability. These results obtained
by a simpler cellulase technique, are corroborated by Nakashima and Orskov (1990)
using the nylon bag technique on ammonia-treated rice straw and Shen et al. (1998b)
using the nylon bag and in vitro gas production techniques on urea-treated straw. It is
interesting that with barley straw, the results are reversed ± untreated leaf is more
degradable than stem but is less improved by ammonia treatment (Ramanzin et al., 1986).
Urea treatment reduced the insoluble ash content of the leaf fraction probably by an
increased extraction of biogenic silica (Shen et al., 1998a). Urea treatment may also
weaken the bonds between the silica-covered cuticle and underlying tissues (Bae et al.,
1997) thus removing an important barrier to digestion and exposing the underlying silicafree tissues to enzymatic action.
The NaOH treatment increased the IVD of both leaf and stem fractions by increasing
their rapidly and slowly degradable fractions. In contrast to urea treatment, the magnitude
of the increase was similar for all straw fractions. Given the absence of similar studies
in the literature, more studies need to be carried out to corroborate these findings. The
enhanced degradability has been ascribed to a solubilisation of total phenolics
(Chesson, 1981), arabinoxylans and cellulose (Lindberg et al., 1984) arising from the
cleavage of alkali-labile lignin-carbohydrate linkages (Alexander et al., 1987; Ternrud
et al., 1988).
Apart from IVD, the leaf and stem also differed in total ash, insoluble ash and
NDF contents. Principal components analysis was therefore used to evaluate the
relative nutritional value of the leaf and stem fractions by accounting for all parameters
instead of only digestibility. Principal components analysis is a versatile though
exploratory technique which has been used to rank straw varieties (Vadiveloo, 1995),
interpret near infra-red spectroscopic data (Bertrand et al., 1987; Grant et al., 1988) and
characterise analytical data (Martin-Alvarez et al., 1988; Martin-Alvarez and Herranz,
1991).
Principal components analysis ranked the leaf fraction higher in nutritive value than the
stem before and after chemical treatment. The practical value of this result is that the
increasingly high leaf content of modern rice straw varieties arising from breeding for
higher grain yield and quality should provide an impetus for the utilisation of rice straw
as a ruminant feed.
64
J. Vadiveloo / Animal Feed Science and Technology 83 (2000) 57±65
Acknowledgements
Technical assistance by Nik Nazri Nik Yusof, Ku Aishah Ku Din and Astifarini Buang
is recorded with thanks. Financial assistance was provided by MARA University of
Technology. Rice straw was provided by the Malaysian Agricultural Research and
Development Institute, Tanjung Karang.
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