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The effect of sodium hydroxide treatment on the chemical composition, digestibility and digestible energy content of wheat, barley and oat straws
Animal Feed Science and Technology, 29 (1990) 73-87 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
73
The Effect of Sodium Hydroxide Treatment on the Chemical Composition, Digestibility and Digestible Energy Content of Wheat, Barley and Oat Straws ANGELA R. MOSS, D.I. GIVENS and JEANNIE M. EVERINGTON
ADAS, Feed Evaluation Unit, Alcester Road, Stratford upon Avon CV37 9RQ (Gt. Britain) (Received 5 August 1988; accepted for publication 18 August 1989)
ABSTRACT Moss, A.R., Givens, D.I. and Everington, J.M., 1990. The effect of sodium hydroxide treatment on the chemical composition, digestibility and digestible energy content of wheat, barley and oat straws. Anim. Feed Sci. Technol., 29: 73-87. Changes in digestible energy (DE) and digestibility in vivo of 10 samples of wheat, barley and oat straw following farm-scale treatment with sodium hydroxide (45 kg NaOH t -1 dry matter (DM)) were studied using sheep. A range of laboratory measurements were also examined for their relationship with digestible organic matter in the dry matter (DOMD) and DE content measured in vivo. These laboratory methods included three estimates of digestibility in vitro, two methods using cellulase and the other using rumen fluid. NaOH treatment reduced the hemicellulose content of the DM (P<0.001) and this resulted in an increased content of cellulose and lignin in the remaining cell wall. The mean increases in DOMD, coefficient of organic matter digestibility (OMD) and DE contents in vivo were 161 g k g - 1, 0.213 and 2.42 MJ kg- 1DM, respectively, although these varied considerably. No significant differences between the straw species were apparent as a result of upgrading and there appeared to be no effect of initial nutritive value of the straw on the degree of response to treatment. No laboratory measurement was found to be an accurate predictor of DOMD in vivo or of DE content.
INTRODUCTION
The production of straw on mixed farms, and the increasing outcry against straw burning, has led to interest in upgrading this material, so that it may contribute more effectively to ruminant animal production. Upgrading on the farm of origin is particularly favourable because transport costs are minimised. Treatment with sodium hydroxide (NaOH) has been shown to be an effective method for upgrading low quality straws (Owen, 1981 ), even though addition of NaOH exacerbates the nitrogen deficiency which already exists in straw (Orskov and Grubb, 1978). These workers observed an interaction between NaOH and urea when added to straw, such that the response in volun0377-8401/90/$03.50
© 1990 Elsevier Science Publishers B.V.
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A.R. MOSSET AL.
tary intake and digestibility to either NaOH or to urea was limited in the absence of the other. The effects of on-farm addition of NaOH on the chemical composition and nutritional value of straw have been noted by Jackson (1978) and Wanapat et al. (1985). The effects on digestibility have been assessed, mainly by laboratory techniques using rumen fluid (Jayasuriya and Owen, 1975; Braman and Abe, 1977; Sundstol et al., 1978; Berger et al., 1979). The work by Berger et al. (1979) indicated that this method may over-estimate the in vivo digestibility of NaOH-treated straws. Other chemical analyses, particularly the fibre fractions have been shown to be worthless as predictors of the nutritive value of untreated and NaOH-treated straws (Sundstol et al., 1978; Barber et al., 1984). The main purpose of this experiment was to examine the effect of farm-scale treatment of wheat, barley and oat straws with NaOH on digestibility and energy value in vivo. In addition, relationships between measurements in vivo and a range of laboratory measurements were studied to assess their ability to predict the in vivo values. MATERIALS AND M E T H O D S
Treatment of straws Ten samples of straw, comprising winter and spring cultivars of wheat (Triticum aestivum ) , barley ( Hordeum vulgare ) and oats (Avena sativa ) were acquired from various farm sources (Table 1). Representative subsamples of these straws were subjected to farm-scale NaOH treatment using a JF SP 2000 for six samples (JF farm machines, 6400 Sanderborg, Denmark) and a Farmhand straw processor for the remaining four samples (Howard-Farmhand Thrige Agro Ltd. Tractor mounted loaders, Wymondham, Norfolk). In both cases the TABLE1 Cultivars of cereal straws Spring cereals
Winter cereals 'Maris Huntsman' (1)1 'Maris Fundin' (1) Unknown (2 )
Wheat
Barley
Oats
'Maris Milk' 'Midas' 'Mazurka' Unknown 'Maris Tabard'
(1) ( 1) (1) ( 1) (1)
~Number of samples examined.
'Peniarth'
( 1)
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
75
machines chopped the straw to approximately 5-cm lengths and about 14 1 of a 32% (w/v) solution of the NaOH was added to give about 45 kg t -1 of straw dry matter (DM). Safety precautions relating to the caustic nature of the NaOH were observed.
Animals and diets Digestibility and digestible energy (DE) content of all straws were measured using mature wether sheep (liveweight 55-85 kg) in metabolism crates at an intake designed approximately to satisfy the animals' DE requirements for maintenance. Daily diets, designed to provide approximately equal DE intakes using untreated and treated straws, consisted of between 200 and 300 g DM of straw and between 600 and 750 g DM of cubed high temperature dried grass. Each diet was given to four animals for a preliminary period of 10 days followed by a 10-day period to measure intake and collect all faeces. Gross energy (GE) intake and energy losses in faeces were measured. All digestibility and energy values attributable to the straw alone were calculated by difference, as described by van Soest (1982).
Laboratory analyses Subsamples of each straw were analyzed for DM content, proximate fractions, and sodium by the methods of MAFF {1981). Neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose and potassium permanganate lignin were determined by the method of Goering and van Soest (1970). HemiceUulose was calculated as the difference between NDF and ADF, both of which were measured on an ash-free basis. Modified acid detergent fibre (MADF) was determined using the method of Clancey and Wilson (1966). The digestible organic matter in the dry matter (DOMD) was determined in vitro using tureen fluid-pepsin according to the method of Tilley and Terry (1963). DOMD in vitro was also determined using a modification of the neutral detergent-cellulase method of Dowman and Collins (1982) and with the pepsin-cellulase method of Jones and Hayward (1975). GE content was measured on the dried straw and fresh homogenised faeces by adiabatic bomb calorimetry. With the faeces, approximately 0.4 g polyethylene accurately weighed were used as a primer for combustion. Soluble lignin was estimated by a modification of the procedure of van Soest et al. (1984). This involved the overnight soaking of 1 g of air-dry straw with 30 ml of a 0.125 M sodium EDTA buffer of pH 7.0. After filtering, the ultraviolet absorbance of the neutral buffer extract was measured at 280 nm using a 1-cm light path.
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A.R.MOSSET AL.
RESULTS
The overall chemical composition of the untreated and treated straws is shown in Table 2. Treated straw had a lower DM content (P < 0.05), owing to the NaOH being applied in solution. The cell-wall content (NDF) of straw treated with NaOH was reduced, mainly because of a reduction in hemicellulose content, which resulted in cellulose and lignin constituting a greater proportion of the remaining cell wall. The GE content of the treated straw was reduced on average by 1.3 MJ kg -1 DM (P<0.001). The absorbence of the buffer extract was significantly higher for the treated straw (P < 0.001 ). Plots of D OMD in vivo and of DOMD in vitro (rumen fluid-pepsin) against absorbence of buffer extracts are presented in Figs. 1 and 2, respectively. Figure 1 shows a poor relationship between the two parameters. This relationship is much improved in Fig. 2. Table 3 shows the effect of treatment on DOMD estimated by three different in vitro methods by cereal type and for the pooled data the overall changes TABLE2
Chemical composition of untreated straws and straws treated with sodium hydroxide (g k g - 1 DM, or as stated) Constituent
Untreated straw
Treated straw
Mean
SD 1
Mean
SD
841 44 429 13 64
51.3 9.8 21.3 3.3 20.0
762 39 416 9 121
87.6 10.0 25.5 1.6 18.6
30.5* 4.3 10.2 1.1' 8.4***
MADF 2
799 523 407 276 91 506
52.8 28.4 15.1 47.1 11.3 34.6
681 511 398 171 95 498
39.2 32.7 18.5 30.9 12.6 33.8
20.8*** 13.4 7.4 17.6"** 5.2 14.9
Sodium
2
1.8
32
13.2
4.0***
18.5
0.38
17.2
Oven dry matter (g k g - , fresh) Crude protein Crude fibre Ether extract Total ash NDF-ashed ADF-ashed Cellulose Hemicellulose Lignin
SED (df=18)
Gross energy ( M J kg -1 D M )
Absorbence of buffer extract
0.112
* P < 0.05; * * P < 0.01; ***P < 0.001.
1 S D - standard deviation. 2MADF = modified acid detergent fibre.
0.036
0.362
0.36
0.16"**
0.070
0.0276***
77
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
& Truted mtw
720
A&
(3 O O _e
Ll L~ 360.
LI
0.060
0.160
0.2~
e
=
0.320
0.400
0.480
Absorban~ units at 280nm
Fig. 1. Relationship between DOMD in vivo and optical density of the neutral buffer extracts at 280 nm. •
Treated straw
~, Untreated straw •
•
640-
£t,
560-
LI
480-
A 400" 0.080
[ 0.160
i 0.240
i 0.320
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Al~orbance units at 280nm
Fig. 2. Relationship between DOMD in vitro and optical density of the neutral buffer extracts at 280 nm.
owing to treatment. All three methods showed significantly increased DOMD following treatment, regardless of cereal type with the exception of oats for the pepsin-cellulase and neutral detergent-cellulase methods. The estimates of DOMD in vitro using pepsin cellulase were lower than for the other two methods. Table 4 shows the mean values for DOMD in vivo, apparent digestibility coefficients and DE for untreated and treated straws. These indicate an overall increase in DOMD and organic matter digestibility coefficient (OMD) in vivo of 161 g kg -1 DM and 0.213, respectively (P<0.001). Crude fibre (CF) and GE digestibility coefficients improved significantly (P < 0.001 ) as a result of
78
A.R. MOSS E T AL
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EFFECTOFNaOHONWHEAT,BARLEYANDOATSTRAWS
79
TABLE 4
Digestibilityvalues and energy values in vivo for untreated straws and straws treatedwith sodium hydroxide Parameter
Untreated straw
Treated straw
SED
Mean
SD
Mean
SD
436
79.9
597
106.5
(df=18) DOMD (g kg -1) Digestibility coefficients Organic matter Crude fibre Crude protein Gross energy Digestible energy (MJ kg- 1 DM )
0.466 0.468 0.009 0.417
0.086 0.070 0.912 0.098
7.83
1.85
0.679 0.753 0.033 0.595
10.25
40.60***
0.114 0.079 0.789 0.116
0.043*** 0.032*** 0.369 0.046"**
2.10
0.86*
*P<0.05; ***P< 0.001.
treatment and the mean increase in DE content was 2.42 MJ kg -1 DM (P<0.05). Table 5 shows by cereal type, the effect of treatment on digestibility and DE, the resulting changes and for the pooled data the overall changes owing to treatment. Wheat and barley straw showed significantly increased digestibility and DE with treatment, and the changes noted were not affected by cereal type. Oat straw also showed increases with treatment though these were not significant. Figure 3 shows the relationship between initial DOMD in vivo and the subsequent changes following treatment by cereal type. This indicates that the straw types were upgraded to a similar extent regardless of cereal type, with the exception of one oat straw. The chemical measurements and digestibility values in vitro, were all examined for their linear relationship with DOMD and DE measured in vivo, to test their suitability for use as predictors for future samples. This indicated that the three techniques for measuring DOMD in vitro produced relationships which accounted for considerably more of the variability of DOMD and DE than other methods, although in all cases they accounted for less than 50% of the variance in the dependent variable. The use of cell wall fractions as predictors gave relationships accounting for less than 10% of the variance, and hence were not pursued further. Details of the relationships based on the three in vitro methods are shown in Table 6. The prediction equations given in Table 6 were developed from the pooled data of untreated and treated straw populations. When considered as two individual populations, their value as predictors diminished. When using N D F cellulase, DOMD in vitro and pepsin-cellulase for untreated straws only, the
80
A.R. MOSS ET AL
03
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EFFECT OF NaOH O N WHEAT, BARLEY A N D OAT STRAWS
81
Zl Wheat straw • Barley straw • Oat straw A
> .E
&
•
210
IE
g .E
140
70-
Initial DOMD content (9 kg-1 )
Fig. 3. Relationship between change in DOMD in vivo content and initial DOMD in vivo content.
TABLE 6 Linear regression of digestible energy content (MJ kg- 1 DM) and of DOMD (g kg- ~) in vivo on various measured parameters in vitro for untreated and treated straws together Independent variable
Constant (SE~)
Slope (SE)
Accountable Residual variance 2 SD
(%) DOMD Neutral detergent-cellulase 75.90 (101.30) Pepsin-cellulase 287.82 (60.43) Rumen fluid-pepsin 143.00 (109.60) Digestible energy Neutral detergent-cellulase 2.005 (2.118) Pepsin-cellulase 5.479 {1.257) Rumen fluid-pepsin 3.141 (2.206)
0.9331 (0.2087) 0.7867 (0.1925) 0.7269 (0.2069)
48.7 44.0 36.2
0.01489 (0.00436) 0.01224 (0.00401) 0.01147 (0.00416)
34.7 29.4 24.8
88.85 92.86 99.11 1.858 1.932 1.994
Standard error. 2Adjusted for degrees of freedom.
residual SD was reduced to 68.92, 77.43, 73.89 and 1.67, 1.85 and 1.73 for the relationships with DOMD in vivo and DE, respectively. With treated straws all accountable variance values were reduced to zero. Figure 4 shows the best relationship, that between DOMD in vivo and neutral detergent cellulase in vitro.
82
A.R. MOSSET AL.
• ~,
Treated straw Untreated straw
750 I 6OO :S 0 r~
o _¢
A
450
LI
300
280
350
420
490
560
630
In vitro neutral detergent-cellulase DOMD (g kg-1 )
Fig. 4. Relationship between DOMD in vivo and neutral detergent-cellulase DOMD in vitro. DISCUSSION
The observed reduction in GE content of 1.3 MJ kg-1 DM for the NaOHtreated straw compared with untreated straw (Table 2) can be shown by calculation to be almost entirely a result of the increase in total ash content. Similarly, Wanapat et al. (1985) showed a reduction in GE of 1.23 MJ kg -1 DM for NaOH-treated barley straw. In contrast, the GE of straws having undergone ammoniation has been shown to be slightly increased compared with untreated straw (Givens et al., 1988). This may have been related to the introduction of the ammonia, which has a GE content of 381 KJ m o l - 1. This suggests some disadvantage to the treatment of straw with NaOH compared with ammonia as the GE is diluted and the high ash and sodium content can limit levels of inclusion in diets (Singh and Jackson, 1971 ). The reduction in total cell-wall content after treatment with NaOH was due almost entirely to a reduction in hemicellulose. There was no significant change in ADF or CF, although CF digestibility increased substantially. This has also been noted by BrAman and Abe (1977) and Wanapat et al. (1985), who explained the increase as being due to solubilization of hemicellulose, increasing the extent and rate of digestion of cellulose and the remaining hemicellulose. As the ADF and CF contents were not altered by treatment, their measurement to indicate upgrading is not likely to be of use and indeed may be misleading. Similar preferential degradation of hemicellulose was noted by Ololade et al. (1970) for straw treated with ammonia. The elevated absorbence of the buffer extracts at 280 nm for the treated compared with the untreated straws can be interpreted as the presence of cleaved buffer-soluble lignin moieties. During NaOH treatment lignin dissociates from the ligno-cellulosic complex, but is still detected as lignin by the
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
83
present assays (Rexen and Vestergaard Thomson, 1976). No change in lignin content was noted upon treatment with N a O H , though elevated absorbences were observed in this study. The measurement of soluble lignin could be an important method of assessingthe efficiencyof treatment with N a O H , as the variabilityin this can be substantial. The observed relationshipbetween D O M D in vitro and the absorbence of the buffer extracts (Fig. 2) was quite good with an accountable variance of 83.1% and a residualS D of 39.7. Similar relationshipshave been noted by Lau and van Soest (1981) and van Soest et al. (1984), though theirwork was based on a mixture of foragestreatedwith eitherammonia or alkali.The relationship between D O M D in vivo and the absorbence of buffer extract was very poor (Fig. 1 ),though there is littleevidence in the literatureto compare with this. Itwas noted that the two samples with the highest absorbence values also had the highest levelsof sodium at 50.0 and 57.5 g kg-i D M , which is equivalent to a N a O H application of 80-90 kg t- i on a D M basis.The D O M D contents in vivo for these samples were 412 and 502 g kg -I, respectively,whilst the D O M D values in vitro were considerably higher at 658 and 651 g kg -~. Evidence from work done by Berger et al. (1979) showed that lambs fed diets with increasing levels of NaOH had increased rates of passage of a chromic oxide marker and decreased ruminal retention times compared with when they were fed the control diet. The increased chromic oxide flow was assumed to indicate reduced retention time of potentially digestible fibre. The mean luminal retention times were considerably shorter than the 48 h used in the Tilley and Terry (1963) tureen fluid-pepsin in vitro digestibilitytechnique which may partially explain the higher in vitro digestibility compared with that measured in vivo. Lower levels of CF digestibility were observed for these samples. This has been noted by other workers who gave the explanation that increased water intake owing to sodium levels diluted the bacterial population, hindering substrateenzyme contact and hence reducing fibre digestion (Baker and Harris, 1947; Koes and Pfander, 1975). Another possible explanation may relate to the osmolarity of the tureen. Bergen (1972) reported that when the osmolarity of the in vitro media was increased above 400 mOsm kg- ~with sodium salts, in vitro cellulose digestion was reduced by 80% or more. There is also some evidence that soluble lignin components such as ferulic and p-coumaric acids may be inhibitory to digestion (Akin, 1982). The observations made in vitro do not, however, establish whether inhibitory effects of soluble phenolics occur in vivo but should be considered a possibility. Another possibility to explain the slow rates of digestion observed in treated straw in vivo (Berger et al., 1980) is that the high levels of solubilized lignin have the effect of removing much of the ionic structures from the plant cell wall, reducing the cation exchange capacity of the matrix which affects the hydratability of the cell-wall surface, and probably microbial attachment and induction of fermentation (McBurney et al., 1981 ). All these factors may act together when
84
A.R. MOSS ET AL.
excessively high levels of N a O H are applied to straw, to give lower levels of digestibilityin vivo. The D O M D measured in vitro by the three different methods showed significant increases with treatment. O n average the D O M D values in vitro did not significantlydifferfrom those measured in vivo, with the exception of the pepsin-cellulasemethod. This method gave values significantlylower than the D O M D measured by the two other in vitro techniques and the D O M D measured in vivo. This has also been noted in herbage (Givens et al.,1989) and a possible explanation is that the neutral detergent-cellulasemethod involves refluxing the sample at high temperature in boiling neutral detergent solution for 60 rain prior to low temperature incubation with cellulase.The high temperature step which does not occur in the pepsin-cellulase method m a y open up the cellwall structure allowing a more extensive degradation during incubation with the enzyme. Overall, D O M D measured in vivo increased significantly(P < 0.001 ) in the straws treated with N a O H (161 g kg-1). Wanapat et al. (1985) measured an increase in D O M D of 113 g kg -I for barley straw treated with N a O H , compared with 186 g kg- ~ in this experiment. The untreated values did not differ between the two experiments, hence the differencesarose as a result of treatment or other undefined factors. Wheat and barley straw showed significantlyincreased digestibilitiesand D E content with treatment. Oat straw also showed increasesthough these were not significant.A n explanation is that there were only two oat straw samples, one of which was treated with excess N a O H (80-90 g kg-1 on D M basis) and hence gave reduced upgrading in vivo. The changes in D O M D in vivo as a result of treatment with N a O H were not affected by cereal type. The mean change with treatment for the two oat straws was approximately half the change for wheat or barley, the reason for these not being significantlydifferent is the small number of samples for oats and the wide range for them, that is changes in D O M D in vivo of 29 and 154. The changes in D O M D in vivo owing to treatment with ammonia were only significantlydifferentfor oat straw compared with wheat and barley straw (Givens et al.,1988). Givens et al. (1988) showed for all cereals a negative relationshipbetween initialdigestibilityand energy value and response to treatment with ammonia. This was not found to be the case with straw treated with N a O H in this experiment. In fact,initialdigestibilityappeared to have no effecton the degree of response to treatment, with the exception of one oat straw, the reasons for which have been described previously. The treatment of straws with N a O H increased the D E content by an average of 2.42 M J kg- ~ D M . Wanapat et al. (1985) showed an increase in D E content upon treatment of barley straw with N a O H of 1.74 M J kg- ~ D M , which was lower than the increase found in this experiment for barley straws (2.48 M J kg -1 D M ) . Although not measured in this experiment, the likelyoverall effectof treat-
EFFECT OF NaOH O N WHEAT, BARLEY A N D OAT STRAWS
85
m e n t on metabolisable energy (ME) content is an increase of 1.96 MJ kg -1 DM, assuming that M E = D E × 0 . 8 1 (Agricultural Research Council, 1965). However, Sundstol (1982) and Wanapat et al. (1985) noted that there may be a substantially increased methane energy loss following treatment of straw with alkali. The degree of increase was dependent upon type of treatment. The implications of this, if true universally, would be to reduce the overall improvement of ME as a result of treatment. An objective of this experiment was to examine several laboratory measurements for their linear relationship with DOMD and DE content, as this has implications for their future use as predictors of these two values. The results indicated that the biological methods were the only ones of value and even these had relatively poor predictive ability. Givens et al. (1988) reported a prediction equation for the DE content of untreated and ammonia-treated straws using DOMD in vitro as the independent variable. That equation is in close agreement with the one produced in this experiment, with a constant of 3.19 compared with 3.14 and a slope of 0.0114 compared with 0.0115, respectively. However, the standard errors were much greater for these coefficients in the present experiment and hence the equation had a much reduced accountable variance. The standard errors of prediction here are high compared with those recorded by Givens et al. (1988) in ammonia-treated straw. A possible explanation is that a smaller number of samples were studied here and the very high levels of NaOH in two of the straws had a strong influence on the relationships for reasons described earlier. These findings imply that with DOMD in vitro the same prediction equation may be used for untreated straws and straws treated with either ammonia or NaOH. When regressions were calculated for the untreated and treated straws separately, the value of all three biologicalmethods as predictorsdiminished considerably.This was largelyowing to the grouping of data for untreated and treated straws into separate swarms. A similar effect has been noted by Mason et al. {1988) when relating cell-wall degradability by cellulase to rumen fluid digestibility in untreated and ammonia-treated straws. This effect considerably reduces the practical value of the equations. This work has shown that the treatment of cereal straws with NaOH is likely, on average, to increase the DOMD content by 161 g kg -1 and the DE content by 2.42 MJ k g - ~ DM. This upgrading has, however, considerable variability. The results of this study with 10 straw samples suggest that none of the three methods used to assess DOMD in vitro is suitable for accurately predicting DOMD in vivo or DE content. ACKNOWLEDGEMENTS
The authors wish to thank the A D A S Analytical Chemistry Department at Wolverhampton for valued analyticalsupport.W e are also gratefulto Dr. D.I.H.
86
A.R.MOSSETAL.
Jones of the Institute for Grassland and Animal Production (Welsh Plant Breeding Station) for pepsin-cellulase measurements.
REFERENCES Agricultural Research Council, 1965. The Nutrient Requirements of Farm Livestock, No. 2 Ruminants. Technical Reviews and Summaries, HMSO, London. Akin, D.E., 1982. Forage cell wall degradation and p-coumaric, ferulic and sinapic acids. Agron. J., 4: 424-428. Baker, F. and Harris, S.T., 1947. Microbial digestion in the rumen and caecum with special reference to the decomposition of structural cellulose. Nutr. Abstr. Rev., 17: 3-12. Barber, W.P., Adamson, A.H. and Altman, J.F.B., 1984. New Methods of Forage Evaluation. In: W. Haresign and D.J.A. Cole (Editors), Recent Advances in Animal Nutrition. Butterworths, London, pp. 161-176. Bergen, W.G., 1972. Rumen osmolarity as a factor in feed intake control of sheep. J. Anim. Sci., 34: 1054-1060. Berger, L.L., Klopfenstein, T.J. and Britton, R.A., 1979. Factors causing greater in vitro than in vivo digestibility of sodium hydroxide treated roughages. In: Proceedings of the XIVth International Grassland Congress, Lexington, KY, pp. 617-619. Berger, L.L., Klopfenstein, T.J. and Britton, R.A., 1980. Effect of sodium hydroxide treatment on rate of passage and rate of ruminal fiber digestion. J. Anim. Sci., 50: 745-749. Braman, W.L. and Abe, R.K., 1977. Laboratory and in vivo evaluation of the nutritive value of NaOH-treated wheat straw. J. Anim. Sci., 46: 496-505. Clancey, M.J. and Wilson, R.K., 1966. Development and application of a new chemical method for predicting the digestibility and intakes of herbage samples. In: Proceedings of the Xth International Grassland Congress, Helsinki, pp. 445-453. Dowman, M.G. and Collins, F.C., 1982. The use of enzymes to predict the digestibility of animal feeds. J. Sci. Food Agric., 33."689-696. Givens, D.I., Adamson, A.H. and Cobby, J.M., 1988. The effect of ammoniation on the nutritive value of wheat, barley and oat straws. II Digestibility and energy value of measurements in vivo and their predictions from laboratory measurements. Anim. Feed Sci. Technol., 19: 173184. Givens, D.I., Everington, J.M. and Adamson, A.H., 1989. The nutritive value of spring grown herbage produced on farms throughout England and Wales over four years. I. The effect of stage of maturity and other factors on chemical composition, apparent digestibility and energy values in vivo. Anim. Feed Sci. Technol., 27: 157-172. Goering, H.K. and Van Soest, P.J., 1970. Forage Fiber Analysis. Agriculture Handbook No 379, USDA, Washington, DC. Jackson, M.G., 1978. Treated straw for animal feeding. FAO Animal Production and Health Paper No. 10. FAO, Rome. Jayasuriya, M.C.N. and Owen, E., 1975. Sodium hydroxide treatment of barley straw: effect of volume and concentration of solution on digestibility and intake by sheep. Anim. Prod., 21: 313-322. Jones, D.I.H. and Hayward, M.V., 1975. The effect of pepsin pretreatment of herbage on the prediction of dry matter digestibility from solubility in fungal cellulase solution. J. Sci. Food Agric., 26: 711-718. Koes, R.M. and Pfander, W.H., 1975. Heat load and supplement effects on performance and nutrient utilisation by lambs fed orchard grass hay. J. Anim. Sci., 40: 313-319. Lau, M.M. and Van Soest, P.J., 1981. Titratable groups and soluble phenolic compounds as indi-
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
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cators of the digestibilityof chemically treated roughages. Anita. Feed Sci. Technol., 6: 123131. Mason, V.C., Hartley, R.D., Keene, A.S. and Cobby, J.M., 1988. The effect of ammoniation on the nutritive value of wheat, barley and oat straws. I. Changes in chemical composition in relation to digestibilityin vitro and cellwall degradability.Anita. Feed Sci. Technol., 19: 159171. McBurney, M.I., van Soest, P.J. and Chase, L.E., 1981. Cation exchange capacity of various feedstuffsin ruminant rations.In: Proceedings of the Cornell Nutrition Conference for Feed Manufacturers, October 1981, Cornell University, Syracuse, NY, pp. 16-23. M A F F (Ministry of Agriculture, Fisheries and Food), 1981. The Analysis of Agricultural Materials.Reference Book 427, H M S O , London. Ololade, B.G., Mowat, D.N. and Winch, J.E., 1970. Effect of processing methods on the in vitro digestibilityof sodium hydroxide treated roughages. Can. J. Anita. Sci.,50: 657-662. Orskov, E.R. and Grubb, D.A., 1978. Validation of new systems for protein evaluation in ruminants by testing the effectsof urea supplementation on intake and digestibilityof straw with or without sodium hydroxide treatment. J. Agric. Sci.,91: 483-486. Owen, E., 1981. Straw: research work. In: B.A. Stark and J.M. Wilkinson (Editors), Upgrading of Crops and By-products by Chemical or Biological Treatments. Ministry of Agriculture, Fisheries and Food, London, pp. 1-9. Rexen, F. and Vestergaard Thomsen, K., 1976. The effect on digestibilityof a new technique for alkalitreatment of straw. Anita. Feed Sci. Technol., 1: 73-83. Singh, M. and Jackson, M.G., 1971. The effectof differentlevelsof sodium hydroxide spray treatment of wheat straw on consumption and digestibilityby cattle.J. Agric. Sci.,77: 5-10. Sundst¢l, F., 1982. Energy utilizationin sheep fed untreated straw, ammonia treated straw or sodium hydroxide treated straw. Proceedings IX Symposium Energy Metabolism of Farm Animals, E A A P Publ. N o 29, pp. 120-123. Sundst¢l, F., Kossila, V., Theander, O. and Thomsen, K.V., 1978. Evaluation of the feeding value of straw: A comparison of laboratory methods in the Nordic countries. Acta Agric. Scand., 28: 10-16. Tilley,J.M.A. and Terry, R.A., 1963. A two-stage technique for in vitro digestion of forage. J. Br. Grassl. Soc., 18: 104-111. Van Soest, P.J., 1982. Nutritional Ecology of the Ruminant. 0 and B Books, Corvallis,OR, pp. 40-41. Van Soest, P.J.,Mascarenhas Ferreira,A. and Hartley, R.D., 1984. Chemical properties of fibre in relationto nutritivequality of ammonia-treated forages.Anita. Feed Sci. Technol., 10: 155164. Wanapat, M., Sundst¢l, F. and Garmo, T.H., 1985. A comparison of alkalitreatment methods to improve the nutritive value of straw. I. Digestibilityand metabolizability. Anita. Feed Sci. Technol., 12: 295-309.
73
The Effect of Sodium Hydroxide Treatment on the Chemical Composition, Digestibility and Digestible Energy Content of Wheat, Barley and Oat Straws ANGELA R. MOSS, D.I. GIVENS and JEANNIE M. EVERINGTON
ADAS, Feed Evaluation Unit, Alcester Road, Stratford upon Avon CV37 9RQ (Gt. Britain) (Received 5 August 1988; accepted for publication 18 August 1989)
ABSTRACT Moss, A.R., Givens, D.I. and Everington, J.M., 1990. The effect of sodium hydroxide treatment on the chemical composition, digestibility and digestible energy content of wheat, barley and oat straws. Anim. Feed Sci. Technol., 29: 73-87. Changes in digestible energy (DE) and digestibility in vivo of 10 samples of wheat, barley and oat straw following farm-scale treatment with sodium hydroxide (45 kg NaOH t -1 dry matter (DM)) were studied using sheep. A range of laboratory measurements were also examined for their relationship with digestible organic matter in the dry matter (DOMD) and DE content measured in vivo. These laboratory methods included three estimates of digestibility in vitro, two methods using cellulase and the other using rumen fluid. NaOH treatment reduced the hemicellulose content of the DM (P<0.001) and this resulted in an increased content of cellulose and lignin in the remaining cell wall. The mean increases in DOMD, coefficient of organic matter digestibility (OMD) and DE contents in vivo were 161 g k g - 1, 0.213 and 2.42 MJ kg- 1DM, respectively, although these varied considerably. No significant differences between the straw species were apparent as a result of upgrading and there appeared to be no effect of initial nutritive value of the straw on the degree of response to treatment. No laboratory measurement was found to be an accurate predictor of DOMD in vivo or of DE content.
INTRODUCTION
The production of straw on mixed farms, and the increasing outcry against straw burning, has led to interest in upgrading this material, so that it may contribute more effectively to ruminant animal production. Upgrading on the farm of origin is particularly favourable because transport costs are minimised. Treatment with sodium hydroxide (NaOH) has been shown to be an effective method for upgrading low quality straws (Owen, 1981 ), even though addition of NaOH exacerbates the nitrogen deficiency which already exists in straw (Orskov and Grubb, 1978). These workers observed an interaction between NaOH and urea when added to straw, such that the response in volun0377-8401/90/$03.50
© 1990 Elsevier Science Publishers B.V.
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A.R. MOSSET AL.
tary intake and digestibility to either NaOH or to urea was limited in the absence of the other. The effects of on-farm addition of NaOH on the chemical composition and nutritional value of straw have been noted by Jackson (1978) and Wanapat et al. (1985). The effects on digestibility have been assessed, mainly by laboratory techniques using rumen fluid (Jayasuriya and Owen, 1975; Braman and Abe, 1977; Sundstol et al., 1978; Berger et al., 1979). The work by Berger et al. (1979) indicated that this method may over-estimate the in vivo digestibility of NaOH-treated straws. Other chemical analyses, particularly the fibre fractions have been shown to be worthless as predictors of the nutritive value of untreated and NaOH-treated straws (Sundstol et al., 1978; Barber et al., 1984). The main purpose of this experiment was to examine the effect of farm-scale treatment of wheat, barley and oat straws with NaOH on digestibility and energy value in vivo. In addition, relationships between measurements in vivo and a range of laboratory measurements were studied to assess their ability to predict the in vivo values. MATERIALS AND M E T H O D S
Treatment of straws Ten samples of straw, comprising winter and spring cultivars of wheat (Triticum aestivum ) , barley ( Hordeum vulgare ) and oats (Avena sativa ) were acquired from various farm sources (Table 1). Representative subsamples of these straws were subjected to farm-scale NaOH treatment using a JF SP 2000 for six samples (JF farm machines, 6400 Sanderborg, Denmark) and a Farmhand straw processor for the remaining four samples (Howard-Farmhand Thrige Agro Ltd. Tractor mounted loaders, Wymondham, Norfolk). In both cases the TABLE1 Cultivars of cereal straws Spring cereals
Winter cereals 'Maris Huntsman' (1)1 'Maris Fundin' (1) Unknown (2 )
Wheat
Barley
Oats
'Maris Milk' 'Midas' 'Mazurka' Unknown 'Maris Tabard'
(1) ( 1) (1) ( 1) (1)
~Number of samples examined.
'Peniarth'
( 1)
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
75
machines chopped the straw to approximately 5-cm lengths and about 14 1 of a 32% (w/v) solution of the NaOH was added to give about 45 kg t -1 of straw dry matter (DM). Safety precautions relating to the caustic nature of the NaOH were observed.
Animals and diets Digestibility and digestible energy (DE) content of all straws were measured using mature wether sheep (liveweight 55-85 kg) in metabolism crates at an intake designed approximately to satisfy the animals' DE requirements for maintenance. Daily diets, designed to provide approximately equal DE intakes using untreated and treated straws, consisted of between 200 and 300 g DM of straw and between 600 and 750 g DM of cubed high temperature dried grass. Each diet was given to four animals for a preliminary period of 10 days followed by a 10-day period to measure intake and collect all faeces. Gross energy (GE) intake and energy losses in faeces were measured. All digestibility and energy values attributable to the straw alone were calculated by difference, as described by van Soest (1982).
Laboratory analyses Subsamples of each straw were analyzed for DM content, proximate fractions, and sodium by the methods of MAFF {1981). Neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose and potassium permanganate lignin were determined by the method of Goering and van Soest (1970). HemiceUulose was calculated as the difference between NDF and ADF, both of which were measured on an ash-free basis. Modified acid detergent fibre (MADF) was determined using the method of Clancey and Wilson (1966). The digestible organic matter in the dry matter (DOMD) was determined in vitro using tureen fluid-pepsin according to the method of Tilley and Terry (1963). DOMD in vitro was also determined using a modification of the neutral detergent-cellulase method of Dowman and Collins (1982) and with the pepsin-cellulase method of Jones and Hayward (1975). GE content was measured on the dried straw and fresh homogenised faeces by adiabatic bomb calorimetry. With the faeces, approximately 0.4 g polyethylene accurately weighed were used as a primer for combustion. Soluble lignin was estimated by a modification of the procedure of van Soest et al. (1984). This involved the overnight soaking of 1 g of air-dry straw with 30 ml of a 0.125 M sodium EDTA buffer of pH 7.0. After filtering, the ultraviolet absorbance of the neutral buffer extract was measured at 280 nm using a 1-cm light path.
76
A.R.MOSSET AL.
RESULTS
The overall chemical composition of the untreated and treated straws is shown in Table 2. Treated straw had a lower DM content (P < 0.05), owing to the NaOH being applied in solution. The cell-wall content (NDF) of straw treated with NaOH was reduced, mainly because of a reduction in hemicellulose content, which resulted in cellulose and lignin constituting a greater proportion of the remaining cell wall. The GE content of the treated straw was reduced on average by 1.3 MJ kg -1 DM (P<0.001). The absorbence of the buffer extract was significantly higher for the treated straw (P < 0.001 ). Plots of D OMD in vivo and of DOMD in vitro (rumen fluid-pepsin) against absorbence of buffer extracts are presented in Figs. 1 and 2, respectively. Figure 1 shows a poor relationship between the two parameters. This relationship is much improved in Fig. 2. Table 3 shows the effect of treatment on DOMD estimated by three different in vitro methods by cereal type and for the pooled data the overall changes TABLE2
Chemical composition of untreated straws and straws treated with sodium hydroxide (g k g - 1 DM, or as stated) Constituent
Untreated straw
Treated straw
Mean
SD 1
Mean
SD
841 44 429 13 64
51.3 9.8 21.3 3.3 20.0
762 39 416 9 121
87.6 10.0 25.5 1.6 18.6
30.5* 4.3 10.2 1.1' 8.4***
MADF 2
799 523 407 276 91 506
52.8 28.4 15.1 47.1 11.3 34.6
681 511 398 171 95 498
39.2 32.7 18.5 30.9 12.6 33.8
20.8*** 13.4 7.4 17.6"** 5.2 14.9
Sodium
2
1.8
32
13.2
4.0***
18.5
0.38
17.2
Oven dry matter (g k g - , fresh) Crude protein Crude fibre Ether extract Total ash NDF-ashed ADF-ashed Cellulose Hemicellulose Lignin
SED (df=18)
Gross energy ( M J kg -1 D M )
Absorbence of buffer extract
0.112
* P < 0.05; * * P < 0.01; ***P < 0.001.
1 S D - standard deviation. 2MADF = modified acid detergent fibre.
0.036
0.362
0.36
0.16"**
0.070
0.0276***
77
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
& Truted mtw
720
A&
(3 O O _e
Ll L~ 360.
LI
0.060
0.160
0.2~
e
=
0.320
0.400
0.480
Absorban~ units at 280nm
Fig. 1. Relationship between DOMD in vivo and optical density of the neutral buffer extracts at 280 nm. •
Treated straw
~, Untreated straw •
•
640-
£t,
560-
LI
480-
A 400" 0.080
[ 0.160
i 0.240
i 0.320
I 0.400
, 0.480
Al~orbance units at 280nm
Fig. 2. Relationship between DOMD in vitro and optical density of the neutral buffer extracts at 280 nm.
owing to treatment. All three methods showed significantly increased DOMD following treatment, regardless of cereal type with the exception of oats for the pepsin-cellulase and neutral detergent-cellulase methods. The estimates of DOMD in vitro using pepsin cellulase were lower than for the other two methods. Table 4 shows the mean values for DOMD in vivo, apparent digestibility coefficients and DE for untreated and treated straws. These indicate an overall increase in DOMD and organic matter digestibility coefficient (OMD) in vivo of 161 g kg -1 DM and 0.213, respectively (P<0.001). Crude fibre (CF) and GE digestibility coefficients improved significantly (P < 0.001 ) as a result of
78
A.R. MOSS E T AL
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EFFECTOFNaOHONWHEAT,BARLEYANDOATSTRAWS
79
TABLE 4
Digestibilityvalues and energy values in vivo for untreated straws and straws treatedwith sodium hydroxide Parameter
Untreated straw
Treated straw
SED
Mean
SD
Mean
SD
436
79.9
597
106.5
(df=18) DOMD (g kg -1) Digestibility coefficients Organic matter Crude fibre Crude protein Gross energy Digestible energy (MJ kg- 1 DM )
0.466 0.468 0.009 0.417
0.086 0.070 0.912 0.098
7.83
1.85
0.679 0.753 0.033 0.595
10.25
40.60***
0.114 0.079 0.789 0.116
0.043*** 0.032*** 0.369 0.046"**
2.10
0.86*
*P<0.05; ***P< 0.001.
treatment and the mean increase in DE content was 2.42 MJ kg -1 DM (P<0.05). Table 5 shows by cereal type, the effect of treatment on digestibility and DE, the resulting changes and for the pooled data the overall changes owing to treatment. Wheat and barley straw showed significantly increased digestibility and DE with treatment, and the changes noted were not affected by cereal type. Oat straw also showed increases with treatment though these were not significant. Figure 3 shows the relationship between initial DOMD in vivo and the subsequent changes following treatment by cereal type. This indicates that the straw types were upgraded to a similar extent regardless of cereal type, with the exception of one oat straw. The chemical measurements and digestibility values in vitro, were all examined for their linear relationship with DOMD and DE measured in vivo, to test their suitability for use as predictors for future samples. This indicated that the three techniques for measuring DOMD in vitro produced relationships which accounted for considerably more of the variability of DOMD and DE than other methods, although in all cases they accounted for less than 50% of the variance in the dependent variable. The use of cell wall fractions as predictors gave relationships accounting for less than 10% of the variance, and hence were not pursued further. Details of the relationships based on the three in vitro methods are shown in Table 6. The prediction equations given in Table 6 were developed from the pooled data of untreated and treated straw populations. When considered as two individual populations, their value as predictors diminished. When using N D F cellulase, DOMD in vitro and pepsin-cellulase for untreated straws only, the
80
A.R. MOSS ET AL
03
o~
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I "0
~ I
°~ "0
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b~ ,.C
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EFFECT OF NaOH O N WHEAT, BARLEY A N D OAT STRAWS
81
Zl Wheat straw • Barley straw • Oat straw A
> .E
&
•
210
IE
g .E
140
70-
Initial DOMD content (9 kg-1 )
Fig. 3. Relationship between change in DOMD in vivo content and initial DOMD in vivo content.
TABLE 6 Linear regression of digestible energy content (MJ kg- 1 DM) and of DOMD (g kg- ~) in vivo on various measured parameters in vitro for untreated and treated straws together Independent variable
Constant (SE~)
Slope (SE)
Accountable Residual variance 2 SD
(%) DOMD Neutral detergent-cellulase 75.90 (101.30) Pepsin-cellulase 287.82 (60.43) Rumen fluid-pepsin 143.00 (109.60) Digestible energy Neutral detergent-cellulase 2.005 (2.118) Pepsin-cellulase 5.479 {1.257) Rumen fluid-pepsin 3.141 (2.206)
0.9331 (0.2087) 0.7867 (0.1925) 0.7269 (0.2069)
48.7 44.0 36.2
0.01489 (0.00436) 0.01224 (0.00401) 0.01147 (0.00416)
34.7 29.4 24.8
88.85 92.86 99.11 1.858 1.932 1.994
Standard error. 2Adjusted for degrees of freedom.
residual SD was reduced to 68.92, 77.43, 73.89 and 1.67, 1.85 and 1.73 for the relationships with DOMD in vivo and DE, respectively. With treated straws all accountable variance values were reduced to zero. Figure 4 shows the best relationship, that between DOMD in vivo and neutral detergent cellulase in vitro.
82
A.R. MOSSET AL.
• ~,
Treated straw Untreated straw
750 I 6OO :S 0 r~
o _¢
A
450
LI
300
280
350
420
490
560
630
In vitro neutral detergent-cellulase DOMD (g kg-1 )
Fig. 4. Relationship between DOMD in vivo and neutral detergent-cellulase DOMD in vitro. DISCUSSION
The observed reduction in GE content of 1.3 MJ kg-1 DM for the NaOHtreated straw compared with untreated straw (Table 2) can be shown by calculation to be almost entirely a result of the increase in total ash content. Similarly, Wanapat et al. (1985) showed a reduction in GE of 1.23 MJ kg -1 DM for NaOH-treated barley straw. In contrast, the GE of straws having undergone ammoniation has been shown to be slightly increased compared with untreated straw (Givens et al., 1988). This may have been related to the introduction of the ammonia, which has a GE content of 381 KJ m o l - 1. This suggests some disadvantage to the treatment of straw with NaOH compared with ammonia as the GE is diluted and the high ash and sodium content can limit levels of inclusion in diets (Singh and Jackson, 1971 ). The reduction in total cell-wall content after treatment with NaOH was due almost entirely to a reduction in hemicellulose. There was no significant change in ADF or CF, although CF digestibility increased substantially. This has also been noted by BrAman and Abe (1977) and Wanapat et al. (1985), who explained the increase as being due to solubilization of hemicellulose, increasing the extent and rate of digestion of cellulose and the remaining hemicellulose. As the ADF and CF contents were not altered by treatment, their measurement to indicate upgrading is not likely to be of use and indeed may be misleading. Similar preferential degradation of hemicellulose was noted by Ololade et al. (1970) for straw treated with ammonia. The elevated absorbence of the buffer extracts at 280 nm for the treated compared with the untreated straws can be interpreted as the presence of cleaved buffer-soluble lignin moieties. During NaOH treatment lignin dissociates from the ligno-cellulosic complex, but is still detected as lignin by the
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
83
present assays (Rexen and Vestergaard Thomson, 1976). No change in lignin content was noted upon treatment with N a O H , though elevated absorbences were observed in this study. The measurement of soluble lignin could be an important method of assessingthe efficiencyof treatment with N a O H , as the variabilityin this can be substantial. The observed relationshipbetween D O M D in vitro and the absorbence of the buffer extracts (Fig. 2) was quite good with an accountable variance of 83.1% and a residualS D of 39.7. Similar relationshipshave been noted by Lau and van Soest (1981) and van Soest et al. (1984), though theirwork was based on a mixture of foragestreatedwith eitherammonia or alkali.The relationship between D O M D in vivo and the absorbence of buffer extract was very poor (Fig. 1 ),though there is littleevidence in the literatureto compare with this. Itwas noted that the two samples with the highest absorbence values also had the highest levelsof sodium at 50.0 and 57.5 g kg-i D M , which is equivalent to a N a O H application of 80-90 kg t- i on a D M basis.The D O M D contents in vivo for these samples were 412 and 502 g kg -I, respectively,whilst the D O M D values in vitro were considerably higher at 658 and 651 g kg -~. Evidence from work done by Berger et al. (1979) showed that lambs fed diets with increasing levels of NaOH had increased rates of passage of a chromic oxide marker and decreased ruminal retention times compared with when they were fed the control diet. The increased chromic oxide flow was assumed to indicate reduced retention time of potentially digestible fibre. The mean luminal retention times were considerably shorter than the 48 h used in the Tilley and Terry (1963) tureen fluid-pepsin in vitro digestibilitytechnique which may partially explain the higher in vitro digestibility compared with that measured in vivo. Lower levels of CF digestibility were observed for these samples. This has been noted by other workers who gave the explanation that increased water intake owing to sodium levels diluted the bacterial population, hindering substrateenzyme contact and hence reducing fibre digestion (Baker and Harris, 1947; Koes and Pfander, 1975). Another possible explanation may relate to the osmolarity of the tureen. Bergen (1972) reported that when the osmolarity of the in vitro media was increased above 400 mOsm kg- ~with sodium salts, in vitro cellulose digestion was reduced by 80% or more. There is also some evidence that soluble lignin components such as ferulic and p-coumaric acids may be inhibitory to digestion (Akin, 1982). The observations made in vitro do not, however, establish whether inhibitory effects of soluble phenolics occur in vivo but should be considered a possibility. Another possibility to explain the slow rates of digestion observed in treated straw in vivo (Berger et al., 1980) is that the high levels of solubilized lignin have the effect of removing much of the ionic structures from the plant cell wall, reducing the cation exchange capacity of the matrix which affects the hydratability of the cell-wall surface, and probably microbial attachment and induction of fermentation (McBurney et al., 1981 ). All these factors may act together when
84
A.R. MOSS ET AL.
excessively high levels of N a O H are applied to straw, to give lower levels of digestibilityin vivo. The D O M D measured in vitro by the three different methods showed significant increases with treatment. O n average the D O M D values in vitro did not significantlydifferfrom those measured in vivo, with the exception of the pepsin-cellulasemethod. This method gave values significantlylower than the D O M D measured by the two other in vitro techniques and the D O M D measured in vivo. This has also been noted in herbage (Givens et al.,1989) and a possible explanation is that the neutral detergent-cellulasemethod involves refluxing the sample at high temperature in boiling neutral detergent solution for 60 rain prior to low temperature incubation with cellulase.The high temperature step which does not occur in the pepsin-cellulase method m a y open up the cellwall structure allowing a more extensive degradation during incubation with the enzyme. Overall, D O M D measured in vivo increased significantly(P < 0.001 ) in the straws treated with N a O H (161 g kg-1). Wanapat et al. (1985) measured an increase in D O M D of 113 g kg -I for barley straw treated with N a O H , compared with 186 g kg- ~ in this experiment. The untreated values did not differ between the two experiments, hence the differencesarose as a result of treatment or other undefined factors. Wheat and barley straw showed significantlyincreased digestibilitiesand D E content with treatment. Oat straw also showed increasesthough these were not significant.A n explanation is that there were only two oat straw samples, one of which was treated with excess N a O H (80-90 g kg-1 on D M basis) and hence gave reduced upgrading in vivo. The changes in D O M D in vivo as a result of treatment with N a O H were not affected by cereal type. The mean change with treatment for the two oat straws was approximately half the change for wheat or barley, the reason for these not being significantlydifferent is the small number of samples for oats and the wide range for them, that is changes in D O M D in vivo of 29 and 154. The changes in D O M D in vivo owing to treatment with ammonia were only significantlydifferentfor oat straw compared with wheat and barley straw (Givens et al.,1988). Givens et al. (1988) showed for all cereals a negative relationshipbetween initialdigestibilityand energy value and response to treatment with ammonia. This was not found to be the case with straw treated with N a O H in this experiment. In fact,initialdigestibilityappeared to have no effecton the degree of response to treatment, with the exception of one oat straw, the reasons for which have been described previously. The treatment of straws with N a O H increased the D E content by an average of 2.42 M J kg- ~ D M . Wanapat et al. (1985) showed an increase in D E content upon treatment of barley straw with N a O H of 1.74 M J kg- ~ D M , which was lower than the increase found in this experiment for barley straws (2.48 M J kg -1 D M ) . Although not measured in this experiment, the likelyoverall effectof treat-
EFFECT OF NaOH O N WHEAT, BARLEY A N D OAT STRAWS
85
m e n t on metabolisable energy (ME) content is an increase of 1.96 MJ kg -1 DM, assuming that M E = D E × 0 . 8 1 (Agricultural Research Council, 1965). However, Sundstol (1982) and Wanapat et al. (1985) noted that there may be a substantially increased methane energy loss following treatment of straw with alkali. The degree of increase was dependent upon type of treatment. The implications of this, if true universally, would be to reduce the overall improvement of ME as a result of treatment. An objective of this experiment was to examine several laboratory measurements for their linear relationship with DOMD and DE content, as this has implications for their future use as predictors of these two values. The results indicated that the biological methods were the only ones of value and even these had relatively poor predictive ability. Givens et al. (1988) reported a prediction equation for the DE content of untreated and ammonia-treated straws using DOMD in vitro as the independent variable. That equation is in close agreement with the one produced in this experiment, with a constant of 3.19 compared with 3.14 and a slope of 0.0114 compared with 0.0115, respectively. However, the standard errors were much greater for these coefficients in the present experiment and hence the equation had a much reduced accountable variance. The standard errors of prediction here are high compared with those recorded by Givens et al. (1988) in ammonia-treated straw. A possible explanation is that a smaller number of samples were studied here and the very high levels of NaOH in two of the straws had a strong influence on the relationships for reasons described earlier. These findings imply that with DOMD in vitro the same prediction equation may be used for untreated straws and straws treated with either ammonia or NaOH. When regressions were calculated for the untreated and treated straws separately, the value of all three biologicalmethods as predictorsdiminished considerably.This was largelyowing to the grouping of data for untreated and treated straws into separate swarms. A similar effect has been noted by Mason et al. {1988) when relating cell-wall degradability by cellulase to rumen fluid digestibility in untreated and ammonia-treated straws. This effect considerably reduces the practical value of the equations. This work has shown that the treatment of cereal straws with NaOH is likely, on average, to increase the DOMD content by 161 g kg -1 and the DE content by 2.42 MJ k g - ~ DM. This upgrading has, however, considerable variability. The results of this study with 10 straw samples suggest that none of the three methods used to assess DOMD in vitro is suitable for accurately predicting DOMD in vivo or DE content. ACKNOWLEDGEMENTS
The authors wish to thank the A D A S Analytical Chemistry Department at Wolverhampton for valued analyticalsupport.W e are also gratefulto Dr. D.I.H.
86
A.R.MOSSETAL.
Jones of the Institute for Grassland and Animal Production (Welsh Plant Breeding Station) for pepsin-cellulase measurements.
REFERENCES Agricultural Research Council, 1965. The Nutrient Requirements of Farm Livestock, No. 2 Ruminants. Technical Reviews and Summaries, HMSO, London. Akin, D.E., 1982. Forage cell wall degradation and p-coumaric, ferulic and sinapic acids. Agron. J., 4: 424-428. Baker, F. and Harris, S.T., 1947. Microbial digestion in the rumen and caecum with special reference to the decomposition of structural cellulose. Nutr. Abstr. Rev., 17: 3-12. Barber, W.P., Adamson, A.H. and Altman, J.F.B., 1984. New Methods of Forage Evaluation. In: W. Haresign and D.J.A. Cole (Editors), Recent Advances in Animal Nutrition. Butterworths, London, pp. 161-176. Bergen, W.G., 1972. Rumen osmolarity as a factor in feed intake control of sheep. J. Anim. Sci., 34: 1054-1060. Berger, L.L., Klopfenstein, T.J. and Britton, R.A., 1979. Factors causing greater in vitro than in vivo digestibility of sodium hydroxide treated roughages. In: Proceedings of the XIVth International Grassland Congress, Lexington, KY, pp. 617-619. Berger, L.L., Klopfenstein, T.J. and Britton, R.A., 1980. Effect of sodium hydroxide treatment on rate of passage and rate of ruminal fiber digestion. J. Anim. Sci., 50: 745-749. Braman, W.L. and Abe, R.K., 1977. Laboratory and in vivo evaluation of the nutritive value of NaOH-treated wheat straw. J. Anim. Sci., 46: 496-505. Clancey, M.J. and Wilson, R.K., 1966. Development and application of a new chemical method for predicting the digestibility and intakes of herbage samples. In: Proceedings of the Xth International Grassland Congress, Helsinki, pp. 445-453. Dowman, M.G. and Collins, F.C., 1982. The use of enzymes to predict the digestibility of animal feeds. J. Sci. Food Agric., 33."689-696. Givens, D.I., Adamson, A.H. and Cobby, J.M., 1988. The effect of ammoniation on the nutritive value of wheat, barley and oat straws. II Digestibility and energy value of measurements in vivo and their predictions from laboratory measurements. Anim. Feed Sci. Technol., 19: 173184. Givens, D.I., Everington, J.M. and Adamson, A.H., 1989. The nutritive value of spring grown herbage produced on farms throughout England and Wales over four years. I. The effect of stage of maturity and other factors on chemical composition, apparent digestibility and energy values in vivo. Anim. Feed Sci. Technol., 27: 157-172. Goering, H.K. and Van Soest, P.J., 1970. Forage Fiber Analysis. Agriculture Handbook No 379, USDA, Washington, DC. Jackson, M.G., 1978. Treated straw for animal feeding. FAO Animal Production and Health Paper No. 10. FAO, Rome. Jayasuriya, M.C.N. and Owen, E., 1975. Sodium hydroxide treatment of barley straw: effect of volume and concentration of solution on digestibility and intake by sheep. Anim. Prod., 21: 313-322. Jones, D.I.H. and Hayward, M.V., 1975. The effect of pepsin pretreatment of herbage on the prediction of dry matter digestibility from solubility in fungal cellulase solution. J. Sci. Food Agric., 26: 711-718. Koes, R.M. and Pfander, W.H., 1975. Heat load and supplement effects on performance and nutrient utilisation by lambs fed orchard grass hay. J. Anim. Sci., 40: 313-319. Lau, M.M. and Van Soest, P.J., 1981. Titratable groups and soluble phenolic compounds as indi-
EFFECT OF NaOH ON WHEAT, BARLEY AND OAT STRAWS
87
cators of the digestibilityof chemically treated roughages. Anita. Feed Sci. Technol., 6: 123131. Mason, V.C., Hartley, R.D., Keene, A.S. and Cobby, J.M., 1988. The effect of ammoniation on the nutritive value of wheat, barley and oat straws. I. Changes in chemical composition in relation to digestibilityin vitro and cellwall degradability.Anita. Feed Sci. Technol., 19: 159171. McBurney, M.I., van Soest, P.J. and Chase, L.E., 1981. Cation exchange capacity of various feedstuffsin ruminant rations.In: Proceedings of the Cornell Nutrition Conference for Feed Manufacturers, October 1981, Cornell University, Syracuse, NY, pp. 16-23. M A F F (Ministry of Agriculture, Fisheries and Food), 1981. The Analysis of Agricultural Materials.Reference Book 427, H M S O , London. Ololade, B.G., Mowat, D.N. and Winch, J.E., 1970. Effect of processing methods on the in vitro digestibilityof sodium hydroxide treated roughages. Can. J. Anita. Sci.,50: 657-662. Orskov, E.R. and Grubb, D.A., 1978. Validation of new systems for protein evaluation in ruminants by testing the effectsof urea supplementation on intake and digestibilityof straw with or without sodium hydroxide treatment. J. Agric. Sci.,91: 483-486. Owen, E., 1981. Straw: research work. In: B.A. Stark and J.M. Wilkinson (Editors), Upgrading of Crops and By-products by Chemical or Biological Treatments. Ministry of Agriculture, Fisheries and Food, London, pp. 1-9. Rexen, F. and Vestergaard Thomsen, K., 1976. The effect on digestibilityof a new technique for alkalitreatment of straw. Anita. Feed Sci. Technol., 1: 73-83. Singh, M. and Jackson, M.G., 1971. The effectof differentlevelsof sodium hydroxide spray treatment of wheat straw on consumption and digestibilityby cattle.J. Agric. Sci.,77: 5-10. Sundst¢l, F., 1982. Energy utilizationin sheep fed untreated straw, ammonia treated straw or sodium hydroxide treated straw. Proceedings IX Symposium Energy Metabolism of Farm Animals, E A A P Publ. N o 29, pp. 120-123. Sundst¢l, F., Kossila, V., Theander, O. and Thomsen, K.V., 1978. Evaluation of the feeding value of straw: A comparison of laboratory methods in the Nordic countries. Acta Agric. Scand., 28: 10-16. Tilley,J.M.A. and Terry, R.A., 1963. A two-stage technique for in vitro digestion of forage. J. Br. Grassl. Soc., 18: 104-111. Van Soest, P.J., 1982. Nutritional Ecology of the Ruminant. 0 and B Books, Corvallis,OR, pp. 40-41. Van Soest, P.J.,Mascarenhas Ferreira,A. and Hartley, R.D., 1984. Chemical properties of fibre in relationto nutritivequality of ammonia-treated forages.Anita. Feed Sci. Technol., 10: 155164. Wanapat, M., Sundst¢l, F. and Garmo, T.H., 1985. A comparison of alkalitreatment methods to improve the nutritive value of straw. I. Digestibilityand metabolizability. Anita. Feed Sci. Technol., 12: 295-309.