Rumen degradation in sacco in sheep of wheat straw
treated with calcium oxide, sodium hydroxide and
sodium hydroxide plus hydrogen peroxide
A.S. Chaudhry
*Department of Agriculture, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK
Received 7 June 1999; received in revised form 28 September 1999; accepted 22 October 1999
Abstract
This split unit study involved two sheep, seven incubation times and four test straws to compare with untreated straw the effect, kgÿ1straw dry matter (DM), of CaO (160 g CaO plus 2 l of water),
NaOH (80 g NaOH in 3 l of water) and alkaline hydrogen peroxide (NaOH plus 132 g H2O2in 3 l
of water, AHP) treatments on composition and rumen degradation in sacco of wheat straw in sheep. After 14 days of storage, each straw was mixed with molasses, dried, ground, weighed into nylon bags and incubated ruminally for various hours in sheep fed daily 1 kg dried grass cubes. After removal, the residues within bags were washed together with unincubated samples (0 h) of straws, dried and analysed for DM, organic matter (OM) and neutral-detergent ®bre (NDF) to estimate nutrient disappearance from straws. The data on nutrient disappearance were ®tted exponentially to estimate quick- (a), slow (b) and predicted (P0.025) degradable fractions and degradation rate (c) for b. NDF and hemicellulose were reduced in treated compared with untreated straw (p< 0.001). Disappearance of nutrients from treated straws was signi®cantly greater than that from untreated straw at almost all incubations (p< 0.001). The a, b, c and P0.025 estimates were signi®cantly
increased by all treatments (p< 0.001). AHP treatment increased straw degradation more than NaOH and CaO treatments. Although, CaO improved rumen degradation less than NaOH, its use to increase straw digestion even moderately may be more desirable because it is readily available, cheap and less dangerous for the users and the environment.#2000 Published by Elsevier Science B.V. All rights reserved.
Keywords:Rumen degradation; Straw; Calcium oxide; Sodium hydroxide; Hydrogen peroxide 83 (2000) 313±323
*Tel.:44-1912226869; fax:44-1912227811.
E-mail address: a.s.chaudhry@newcastle.ac.uk (A.S. Chaudhry).
1. Introduction
Rumen degradation is critical in the utilization of cereal straws by ruminant animals. However, using straws as an energy feed for ruminants is limited because their cell walls contain three dimensional structures that are less available for microbial degradation in the rumen (Wilkie, 1979; Sundstol and Owen, 1984; Chaudhry, 1998a). Consequently, major nutrients from straws escape digestion and are wasted as faeces by the ruminants. However, the energy value of straws can be increased if their cell wall structure is modi®ed. Chemical treatments can modify cell wall to increase microbial degradation and thus utilization of straws by ruminants (Jung et al., 1993).
Recently, Chaudhry (1997) following reports from Gould (1984) and Kerley et al. (1986) con®rmed the effectiveness of alkaline hydrogen peroxide (NaOHH2O2, AHP)
to modify cell wall composition and in vitro dry matter digestibility (DMD) of wheat straw. However, the need for a high amount (13 or 26 l kgÿ1
DM) of water and NaOH to maintain the pH of AHP around 11.5 was considered a limitation for the on-farm application of AHP. In another series of in vitro experiments, although the amount of water was reduced, the use of calcium oxide (CaO) as an alternative alkali to maintain the ef®cacy of AHP treatment even at a pH of 11.5 did not succeed (Chaudhry, 1998b). In contrast, CaO alone increased the in vitro DMD of wheat straw under speci®c conditions. In another study, Chaudhry (1998c) supported the ef®cacy of CaO and NaOH alone and AHP in improving composition, nutrient digestion and fermentation of straw-based diets in sheep. The increased digestion was perhaps due to the increased rate and extent of straw degradation by rumen microbes. However, this assumption can only be substantiated if the rumen degradation kinetics were studied. Moreover, as Chaudhry (1998c) fed each straw together with a concentrate to sheep, it was not clear whether the increased digestion was solely a consequence of a chemical treatment or was partly due to its interaction with the concentrate.
Since rumen is the primary site of digestion for ®brous feeds in ruminants, it is important to monitor degradation kinetics in response to modi®cation of cell wall caused by alkali treatments. This may be achieved by using in sacco technique which is quicker and cheaper than whole animal studies. Therefore, this study examined the effect of CaO, NaOH and AHP on the rate and extent of degradation in sacco of wheat straw in sheep. Treatment with CaO was tested as a cheap and a safe alternative to NaOH in improving the rate and extent of straw degradation whereas NaOH also served as a control for AHP.
2. Materials and methods
2.1. Chemicals, straw and treatments
NaOH (32% w/w, speci®c gravity 1.35) and H2O2(27.5% w/w, speci®c gravity 1.1) as
solutions and CaO as a ®ne powder were purchased from, respectively, Ellis and Everrard, and BDH, UK and used to treat wheat straw variety Norman (straw, chopped through an 8 mm sieve) as described by Chaudhry (1998c). Each treatment was applied on kgÿ1
2.1.1. Control
Untreated straw served as a control.
2.1.2. CaO
The straw was mixed with 2 l of water in a mixer, dusted with 160 g CaO and the contents were then re-mixed for ca. 1 h. The treated straw was then placed into a plastic bag, tied up and stored at ca. 128C. The added amount of CaO was 160 g kgÿ1straw DM with a liquid : straw ratio of 2 : 1 and an initial pH of >13.
2.1.3. NaOH
The straw was mixed with 3 l of solution containing 80 g NaOH for ca. 1 h, placed into a plastic bag and stored as described above. The added amount of NaOH was 80 g kgÿ1
DM at a liquid : straw ratio of 3 : 1 with an initial pH of >12 during 1 h of mixing. The NaOH-treated straw also served as a control for AHP-treated straw.
2.1.4. AHP
Another batch of NaOH-treated straw was prepared as described in Section 2.1.3. After 27 h pre-soaking, 480 ml of H2O2solution containing 132 g H2O2were added, mixed for
5 h and stored as described earlier. During mixing, the pH of treated straw was monitored at 30-min intervals and was observed to remain around 11.50.2. The amounts of added NaOH and H2O2were 80 and 132 g kg
ÿ1
straw DM, respectively.
2.2. Preparation of straws for rumen incubation
After 14-days storage in an open shed (average temperature 128C), each kg DM of each treated and untreated straw was separately mixed with 100 g molasses (Molaferm-50; United Molasses) in line with that described by Chaudhry (1998c). No other reason for adding molasses into straws is offered. As hot water was added into molasses to facilitate mixing, the molasses DM was reduced from 65 to 55% and hence the added molasses in straw on DM basis was 55 g kgÿ1. The straws were dried and ground through a 4 mm sieve before in sacco rumen incubations.
2.3. Animals, housing and feeding
Two SuffolkMule wether sheep weighing between 60 and 64 kg were used in this experiment. The sheep were ®tted with rumen cannulae and housed individually on concrete ¯oors covered with sand. Each sheep was adapted to a ®xed daily intake of 1 kg dried grass cubes containing 160 g crude protein for 14 days before in sacco degradability was examined.
2.4. Experimental design and chemical analysis
A split-unit design involved two sheep (blocks), seven incubation times (main units) and four test straws (sub-units) to study in sacco degradability of untreated and treated
straws. Duplicate samples of ca. 2.5 g DM of each test straw were weighed into separate nylon bags which were then tied up by a plastic string to a 16 cm long ¯exible polypropylene tube and suspended in the rumen of each sheep for 6, 12, 24, 48, 72 and 96 h. Given the limited rumen capacity of sheep, the samples were incubated as groups so that only one group of four straws in duplicate was incubated in the rumen at any given time. Samples of 0 h representing water-soluble fraction (a) were prepared by washing bags, in duplicate, containing test straws for 30 min in a domestic washing machine. After removal from the rumen at each incubation time, the residues within bags were washed, freeze dried, ground through a 1 mm sieve and analysed together with unincubated samples for DM, organic matter (OM) and neutral detergent ®bre (NDF) (Van Soest et al., 1991). Disappearance of nutrients from each straw was calculated by difference between nutrient composition of the unwashed and unincubated dried sample of that straw and its residue after each incubation time in the rumen. Disappearance was assumed to be due to degradation in the rumen. Samples of unwashed and unincubated straws were also analysed for acid-detergent ®bre (ADF) and acid-detergent lignin (ADL) to estimate cellulose and hemicellulose contents for each straw by subtracting ADL from ADF and ADF from NDF, respectively.
2.5. Calculations and statistical analysis
The data from in sacco studies were ®tted into the exponential model {pab(1ÿeÿct)} of érskov and McDonald (1979) by using the Maximum
Likelihood Programme to obtain estimates ofa,b andc for each straw in each sheep. Here, a represented water-soluble (or quickly degradable) and b insoluble (or slowly-degradable) fractions whereascdegradation rate ofbandtthe hours of incubation. While apparent degradability was represented by ab (asymptote), predicted rumen degradability (P0.025) for each straw was also calculated from an equation,
Pa(bc/ck), where k was the rumen out¯ow rate at 0.025 per hour (h) for animals fed at a slightly above maintenance level (AFRC, 1993). The estimates ofa,b,c, asymptoteandP0.025were statistically analysed by using ANOVA in GENSTAT to test
the effect of chemical treatments on cell wall composition and the rate and extent of in sacco degradability of straw.
3. Results
3.1. Cell wall composition
3.2. Nutrient disappearance
Figs. 1±3 illustrate the patterns of DM, OM and NDF disappearance from each test straw during rumen incubation for various times together with SED for each incubation Table 1
Cell wall composition (g kgÿ1OM) of molassed untreated and treated straws
Composition Straw treatmentsa
Untreated CaO NaOH AHP SED
Neutral detergent ®bre 841 a 676 c 781 b 776 b 16
Cellulose 451 c 528 b 533 b 562 b 13
Hemicellulose 259 a 29 b 67 b 23 b 26
Lignin 104 c 92 d 129 a 115 b 4
aUntreated, CaO, NaOH and AHP were respectively, untreated, CaO-, NaOH- and alkaline hydrogen
peroxide (NaOHH2O2, AHP) treated wheat straw. After 14-days storage at 128C, molasses was added to each
straw at 55 g molasses DM kgÿ1 straw DM; neutral detergent ®bre represented total cell wall; means with
different superscripts in a same row were signi®cantly different.
Fig. 1. Pattern of disappearance of dry matter (DM) from molassed wheat straw, untreated (Untr) or treated respectively with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2(AHP) during rumen incubation for various
times in sheep. The lines represent data being ®tted for each test straw according to the exponential model. The standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 6, 29, 18, 14, 26, 19 and 5, respectively.
time. The disappearance of DM, OM and NDF was signi®cantly greater for treated straws than for untreated straw at almost all incubation times (p< 0.001). The incubation at 6 h was an exception where disappearance of NDF from CaO-treated straw was not signi®cantly greater than that of untreated straw. However, the loss of NDF from CaO-treated straw on washing with water was less than unCaO-treated straw (p< 0.001). In contrast, the losses of DM and OM from treated straws on washing with water (0 h) were greater than that from untreated straw. Signi®cant differences between treatments for the disappearance of DM, OM and NDF during each incubation time were also observed (p< 0.001). AHP treatment caused the greatest disappearance of DM, OM and NDF from straws followed by NaOH and CaO. Untreated straw showed increased disappearance of DM, OM and NDF with increasing incubation time to 96 h (p< 0.001). In contrast, the disappearance of nutrients from NaOH and AHP straws almost peaked at 48 h whereas the disappearance from CaO straw continued to increase to 72 h (p< 0.001).
Fig. 2. Pattern of disappearance of organic matter (OM) from molassed wheat straw, untreated (Untr) or treated respectively, with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2 (AHP) during rumen incubations for
3.3. Degradation characteristics
Table 2 presents estimates of a, b, ab, c and P0.025 for untreated and treated
straws.
3.3.1. Quickly (a) and slowly degradable (b) fractions
Quickly- and slowly-degradable fractions for DM, OM and NDF were signi®cantly affected by treatments (p< 0.001). Quickly degradable fractions of DM, OM and NDF were greatest for AHP treated straw compared with untreated or other treated straws (p< 0.001). In contrast, the slowly degradable fractions of DM and NDF and OM were greatest respectively for CaO- and NaOH-treated straws. However, the quickly degradable fraction of NDF in untreated straw was greater compared with NaOH- and CaO-treated straws (p< 0.01) but was less in all straws compared with AHP-treated straw (p< 0.01).
Fig. 3. Pattern of disappearance of neutral detergent ®bre (NDF) from molassed wheat straw, untreated (Untr) or treated, respectively with CaO (CaO), NaOH (NaOH) and NaOH plus H2O2(AHP) during rumen incubation for
various times in sheep. The lines represent data being ®tted for each test straw according to the exponential model. The standard errors of difference for 0, 6, 12, 24, 48, 72 and 96 h of incubation were 7, 35, 31, 15, 20, 26 and 7, respectively.
3.3.2. Degradation rate (c) and predicted degradability (P0.025)
The degradation rates of DM, OM and NDF were signi®cantly faster for treated compared with untreated straw (p< 0.001). However, AHP treatment increased degradation rates most compared with NaOH and CaO. Predicted degradability of DM, OM and NDF was signi®cantly greater for treated compared with untreated straw (p< 0.001). However, predicted degradability was greatest for AHP (p< 0.001) compared with NaOH and CaO.
4. Discussion
Following previous studies (Chaudhry, 1998b, c), this study examined the effects of already determined best levels of CaO, NaOH and AHP treatments on rumen degradation in sacco in sheep. While treatments modi®ed cell wall composition and increased in sacco rumen degradation of straw compared with untreated straw, the extent of increase depended on the type of chemical used. The reasons for those differences between treatments are discussed by comparing the results with published information.
The reduction in NDF by different treatments was mainly due to the decreased hemicellulose content of straw (Table 1). The chemical treatments may have removed some linkages within hemicelluloses and thus enhanced their solubility in detergent Table 2
Degradable fractions of nutrients (g kgÿ1) in molassed untreated, CaO-, NaOH- and AHP-treated wheat straws
after in sacco rumen incubations in sheep (Means with standard error of difference, SED)a
Parameters Untreated CaO NaOH AHP SED
Dry matter
a 108 279 278 383 4.6
b 433 644 599 559 15
c(per hour) 0.015 0.021 0.049 0.054 0.002
ab 541 923 877 942 18
Pat 0.025 274 573 675 765 8
Organic matter
a 113 199 189 290 9
b 444 643 674 644 20
c(per hour) 0.014 0.034 0.049 0.051 0.002
ab 557 842 863 934 20
P0.025 272 570 635 722 10
Neutral detergent ®bre
a 65 ÿ34 23 111 10
b 493 842 822 811 95
c(per hour) 0.012 0.036 0.048 0.054 0.005
ab 558 808 845 922 89
P0.025 225 463 563 665 26
aAHP, alkaline hydrogen peroxide (NaOHH
2O2);aandbrespectively, quickly and slowly degradable
fractions;c,degradation rate ofb; abandP0.025 represent apparent (asymptote) and predicted extent of
solutions (Wilkie, 1979; Chaudhry, 1998a, c). The modi®ed cell wall composition of straw in response to NaOH and AHP was comparable to that of Chaudhry (1997, 1998c) for the same levels of those chemicals. However, the absolute NDF in untreated and NaOH and AHP-treated straws of this study were greater than those of Chaudhry (1997). The variation in NDF was perhaps due to the use of different straw variety and method by Chaudhry (1997).
The ranking of untreated and treated straws based on an increased in sacco degradation was comparable to those of in vitro (Chaudhry, 1998b) and in vivo (Chaudhry, 1998c) digestibility of straw treated with the same chemicals. However, the absolute degradation for various straws differed with the change in chemicals and incubation times. The NDF disappearance from straws was relatively less than those of DM and OM during all incubation times. The difference between losses of different nutrients was larger during the initial 12 h of incubation. The NDF loss from untreated straw (368 g kgÿ1
) after rumen incubation of 96 h was less than that (500 g kgÿ1
) of Miller and Oddoye (1989) for the same incubation time. The degradation rate (c, 0.012) for NDF was also slower than that (0.042) of the same researchers. The difference may be attributed to the difference in straw variety (Huntingdon and Givens, 1995), particle size (Hovell et al., 1987), and rumen conditions and diet composition of the host animal (Ramanzin et al., 1997). In general, the degradation pattern for untreated and NaOH and AHP-treated straws of this experiment agreed with published studies (Bharghava et al., 1989; Adebowale et al., 1989). The nutrient disappearance from CaO-treated straw was reasonably close to that from NaOH-treated straw at 72 h of incubation and thereafter. However, the degradation pattern of CaO of this study cannot be compared with that in the literature because almost no published information on the degradation pattern of CaO-treated straws could be found.
Theabvalue (541 g kgÿ1
) for DM in untreated straw of this study was comparable to that (599 g kgÿ1
) reported by Adebowale et al. (1989). Theabvalue for DM in CaO was greater compared with NaOH. This represented the greater washing loss in water of residual CaO from straw simply because more CaO than NaOH was initially used to treat the straw. However, it is noted that this variation was not caused by the washing loss of added molasses since the same amounts of molasses were added across treatments. The ab values of OM and NDF for CaO and NaOH were closer to each other despite signi®cantly different degradation rates (c values, 0.034 vs. 0.049 for OM;and 0.036 vs. 0.048 for NDF). The non-signi®cant difference between CaO and NaOH for the apparent extent of degradation (aborasymptote) in this study, was comparable to that of in vitro digestibility (Chaudhry, 1998b) but was contrary to the in vivo digestibility (Chaudhry, 1998c) where NaOH was better than CaO. However, when degradation (c) and rumen out¯ow rates (k) were taken into consideration, the differences between the predicted degradability (P0.025) of different straws were comparable to those of in vivo digestibility
(Chaudhry, 1998c). The decreased losses of DM and OM from untreated and DM from CaO at 6 h were perhaps due to the particle-associated microbes that increased residual weights of straw during incubation.
AHP was the most effective treatment in improving degradation of wheat straw. The results agreed with the previous reports where AHP was better than its NaOH-control and CaO in improving in vitro and in vivo digestibility of wheat straw (Chaudhry, 1997,
1998b, c). Although CaO greatly reduced NDF and lignin of straw, it did not improve rumen degradation as much as NaOH and AHP did. It may be due to the greater effect of CaO on the lignin molecule (Table 1) to release phenolics to inhibit rumen microbes and consequently rumen degradation of straw (Marvin et al., 1996). In contrast, Silanikove (1994) reported a greater deligni®cation in cotton straw when NaOH instead of CaO was used as an alkali in AHP treatment. However, no difference was reported between the two chemicals for in vitro digestibility of cotton straw. Chaudhry (1998a, b, c), has discussed the potential and problems associated with chemical treatments in improving nutritive value of cereal straws. In summary, the study supported the hypothesis that the increased digestion of cereal straws by ruminants was a consequence of increased rate and extent of their rumen degradation.
In conclusion, CaO modi®ed cell wall composition and increased rumen degradation in sacco of wheat straw and therefore could be used as an alternative to NaOH to increase the digestible OM intake of sheep fed treated straw. Although CaO improved rumen degradation less than NaOH did, its use to increase straw digestion even moderately may be more desirable because it is readily available, cheap and less dangerous for the users and the environment. However, it is essential to reduce the level of chemicals but without reducing their effect to improve straw digestion in ruminants. It is also essential to perform a cost-bene®t analysis before applying treatment on-farm to improve low quality forages. The bene®ts of using chemical treatments would be determined by the availability and price of other animal feeds in different regions of the world at a particular time.
Acknowledgements
ASC thanks Dr. E.L. Miller for his invaluable advice and comments during studies at the University of Cambridge, UK and Mr. Allan Lisle from the University of Queensland at Gatton, Australia for his statistical advice.
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