Improving utilization of crop residues. Evaluation of two chemicals used to improve digestibility of crop residues

Two chemical treatments involving chelating metal caustic swelling (CMCS) and sodium hydroxide (NaOH) were evaluated for their ability to affect in vitro dry matter and in vitro cellulose disappearance (IVDMD and IVCD, respectively), dry matter disappearance in sacco and the chemical composition of two low-quality crop residues, cornstalks (CS) and soya bean residue (SBR). At $\text{chemical}\text{substrate}$ ratios ranging from 0.25:1 to 5:1, linear increases in IVCD of both roughages were noted. Improvements in IVCD of CS and SBR were noted at 1:1, 3:1 and 5:1$\text{chemical}\text{substrate}$ ratios, regardless of whether the treated roughages were used immediately after treatment (fresh basis) or preserved by drying or freezing. Decreased concentrations of neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL) and crude protein (CP) resulted from chemical treatment. No effects of the water component of the solvent solutions were observed. Dry matter disappearance in sacco of CMCS- and NaOH-treated roughages was increased at all $\text{chemical}\text{substrate}$ ratios tested. Treatment of either roughage with CMCS resulted in greater digestibility in sacco than did treatment with NaOH. Treatment of CS with CMCS resulted in higher rates of digestion than did treatment with NaOH. No differences in rates of digestion of SBR were noted between chemicals. Both chemicals were more effective in improving digestibility of CS than of SBR.     

Effect of ozone and sodium hydroxide treatments on the degradability of cotton straw monosaccharides by rumen microorganisms

Summary Cotton straw (CS) was treated with ozone and sodium hydroxide and the effect of the treatments on the in vitro digestibility of monosaccharides in the whole material and in cell walls was studied. The digestibility of the major components — glucose and xylose in the untreated whole material was low, 26.3 and 14.3%, respectively, whereas that of the minor components was high, in the range of 60–70%. Ozonation resulted in an increase in digestibility of most of the sugars, with a particular effect on glucose and xylose, the digestibility of which was raised to 72 and 67%, respectively. Sodium hydroxide exerted a modest effect, increasing the in vitro digestibility values for glucose to 35.7% and for xylose to 32.3%.The digestibility of glucose, xylose and uronic acids in the cell wall of the untreated material was 19.7, 8.73 and 21.9%, respectively, whereas the values for the minor components ranged between 50 and 60%. The ozone treatment increased the in vitro degradability of the residual glucose, xylose and uronic acids to 63.7, 26.3 and 53.5%, respectively.There was a lag time of between 12 and 24 h before the rumen bacteria started to hydrolyse the cell wall glucose, xylose and uronic acids. The lag time for those cell wall sugars in the ozonated CS was the longest (24 h) but their rate of in vitro digestion during the last 24 h was higher in the ozonated than in the untreated or sodium hydroxide-treated cotton straw. The practical implications of the above-mentioned findings are discussed.     

Animal digestive strategies versus anaerobic digestion bioprocesses for biogas production from lignocellulosic biomass

Herbivorous mammals and wood-eating insects are fairly effective in the digestion of plant polymers, such as lignocellulosics. In order to improve methane production from the lignocellulosic biomass, several kinds of anaerobic digestion processes derived from animal models have been devised. However, the rates of biodegradation occurring in the anaerobic bioreactors still remain lower than in animal guts. The effectiveness of the digestive systems of those animals results from the concerted action of the various enzymes (e.g. cellulases, xylanases, esterases, ligninases) produced in their guts as well as their integration with mechanical and chemical actions. Powerful pretreatment (prefermentation) operations are integrated to and support efficiently the microbial fermentation system, e.g. the rumination (i.e. mechanical) in ruminants and the secretion of endogenous cellulases (i.e. enzymatic) or the alkaline treatment (chemical) at mid-way in xylophagous insects. The oxygen gradients along the gastrointestinal tract may also stimulate the hydrolytic activities of some microbial populations. In addition, the solid retention time, the digesta flow and the removal of the end-products are well ordered to enable animals to thrive on a complex polymer such as lignocellulose. At the same time, technologies were developed to degrade lignocellulosic biomass, such as the rumen derived anaerobic digestion (RUDAD) process and the rumen simulating technique (RUSITEC), more elaborated and using rumen microbial consortia. Overall, they showed that the fermentation taking place in the rumen fermentation and even in the hindgut are biological processes that go beyond the limited environmental conditions generally found in anaerobic digesters. Hence, knowledge on herbivores' digestion mechanisms might be better exploited in the design and operation of anaerobic digesters. This literature review is a cross-analysis of the relevant information about the digestive strategies of herbivorous and wood-eating animals and the bioengineering techniques in lignocelluloses degradation. The aim is to highlight strategies of animals' digestion simulation for more effective anaerobic digestion of lignocellulosic compounds and other solid residues.     

Effect of feeding dehydrated and ensiled tanniferous sainfoin (Onobrychis viciifolia) on nitrogen and mineral digestion and metabolism of lambs

The effects of tanniferous sainfoin on digestion and metabolism have been investigated in 12 lambs in an incomplete cross-over design (n = 6). Effects of condensed tannins (CT) were evaluated by comparing dehydrated and ensiled sainfoin treated with and without polyethylene glycol (PEG). Dehydrated and ensiled grass-clover mixtures served as controls. The lambs were fed the treatment diets, including a mineral supplement, for 21 d. During the last 7 d excreta, rumen fluid and blood were sampled. The CT of sainfoin decreased rumen fluid ammonia concentration (p < 0.001) and increased the plasma concentration mainly of essential amino acids (p < 0.001). Body retention of phosphorus, calcium and magnesium was lower with sainfoin compared to PEG-treated sainfoin (p < 0.05). Sainfoin without PEG resulted in lower digestibilities of organic matter and neutral detergent fibre than sainfoin with PEG and the grass-clover mixture (p < 0.001). Ensiling of sainfoin led to the lowest N-retention. In conclusion, the reduction in ruminal ammonia and urine-N losses by sainfoin CT did not improve N-retention.     

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

The degradation of plant cell walls by ruminants is of major economic importance in the developed as well as developing world. Rumen fermentation is unique in that efficient plant cell wall degradation relies on the cooperation between microorganisms that produce fibrolytic enzymes and the host animal that provides an anaerobic fermentation chamber. Increasing the efficiency with which the rumen microbiota degrades fiber has been the subject of extensive research for at least the last 100 years. Fiber digestion in the rumen is not optimal, as is supported by the fact that fiber recovered from feces is fermentable. This view is confirmed by the knowledge that mechanical and chemical pretreatments improve fiber degradation, as well as more recent research, which has demonstrated increased fiber digestion by rumen microorganisms when plant lignin composition is modified by genetic manipulation. Rumen microbiologists have sought to improve fiber digestion by genetic and ecological manipulation of rumen fermentation. This has been difficult and a number of constraints have limited progress, including: (a) a lack of reliable transformation systems for major fibrolytic rumen bacteria, (b) a poor understanding of ecological factors that govern persistence of fibrolytic bacteria and fungi in the rumen, (c) a poor understanding of which glycolyl hydrolases need to be manipulated, and (d) a lack of knowledge of the functional genomic framework within which fiber degradation operates. In this review the major fibrolytic organisms are briefly discussed. A more extensive discussion of the enzymes involved in fiber degradation is included. We also discuss the use of plant genetic manipulation, application of free-living lignolytic fungi and the use of exogenous enzymes. Lastly, we will discuss how newer technologies such as genomic and metagenomic approaches can be used to improve our knowledge of the functional genomic framework of plant cell wall degradation in the rumen.     

Simple Method to Remove Completely Ciliate Protozoa of Adult Ruminants

Dioctyl sodium sulfosuccinate (Aerosol OT) has been used in a remarkably short period to obtain rumen ciliate-free cows. Two 30-g doses of Aerosol OT given on consecutive days appeared to effectively eliminate all types of rumen ciliate protozoa without harming the health of the host animal. Measurement of the rumen metabolic parameters of gas production, carbon dioxide to methane ratio, pH value, volatile fatty acids, ammonia, and in vitro cellulose digestion, along with total amylolytic streptococci counts of the rumen contents, showed that conditions in rumens of defaunated animals are normal 4 days after such treatment. It appears that such animals may be used in ruminal studies that require defaunated animals.     

Influence of storage time and temperature on in vitro digestion of neutral detergent fibre at 48 h, and comparison to 48 h in sacco neutral detergent fibre digestion

The effect of within-day delays of 0.5, 2.5, 4.5 and 6.5 h between collection of rumen fluid from a cow and initiation of in vitro fermentation, as well as storage of rumen fluid for 48 h at either −24°C or 6, 22 and 39°C, on in vitro digestion of neutral detergent fibre (NDF) at 48 h was determined. In addition, the 48 h in vitro digestion of NDF, determined with a minimum time delay (i.e., 0.5 h) between collection from the cow and initiation of incubation, was compared to NDF digestion determined in sacco at 48 h. Rumen inoculum from a single cow was utilized in a thrice replicated incubation with whole crop alfalfa, corn, cereal and sudangrass forages of a lower and higher quality. The same cow was used as the host for the in sacco bags. The in vitro procedure used a bulk procedure with 5.0 cm × 5.5 cm multi-weave polyethylene polyester polymer bags that retained particles of 25 mm and larger. The in sacco procedure used the same bags retained in a large mesh bag. A within-day time delay of up to 6.5 h between collection of rumen fluid from the cow and initiation of in vitro fermentation had no impact on measured 48 h in vitro digestion of NDF. In contrast, no temperature dependent storage procedure maintained 48 h in vitro digestion of NDF at levels determined with no 48 h storage, although high quality alfalfa was least affected by any storage procedure. The 48 h in vitro digestion of NDF, determined using the minimum time delay between collection from the cow and initiation of the incubation, was higher than values obtained in sacco. Results show that this bulk in vitro procedure resulted in higher 48 h digestion of NDF than those determined with a similar in sacco procedure, thereby suggesting that laboratories located some distance from the donor animal can utilize in vitro procedures to accurately estimate 48 h digestion of NDF. However, storage of rumen fluid for 48 h, by any temperature dependent procedure examined, in order to facilitate fewer trips to the donor animal, or trips of substantially longer duration, will underestimate 48 h digestion of NDF to an extent that depends upon the forage incubated.     

Evaluation by electron microscopy and anaerobic culture of types of rumen bacteria associated with digestion of forage cell walls.

Different morphological types of rumen bacteria which degraded cell walls of forage grasses with various in vitro digestibilities were evaluated with electron microscopy. The majority of these bacteria (i.e., about 70% or more) consisted of two distinct types: (i) encapsulated cocci and (ii) irregularly shaped bacteria, resembling major fiber digesters found in the rumen. Each type was capable of degrading structurally intact cell walls. Differences (P less than or equal to 0.02) in the percent ratio of encapsulated cocci to irregularly shaped bacteria were observed between Bermuda grass and fescue; the ratio of encapsulated cocci to irregularly shaped bacteria between Bermuda grass and orchard grass was similar and variations were high. The proportion of irregularly shaped bacteria usually increased with increased time of digestion. Differences (P greater than 0.1) were not found in the percentage ratio of encapsulated cocci to irregularly shaped bacteria attached to specific tissue types in either Bermuda grass or fescue. However, encapsulated cocci tended to be more prevalent on sclerenchyma than other tissues in Bermuda grass, but less prevalent on sclerenchyma than other tissues in fescue. Transmission electron microscopy of tissue digestion of rapidly degraded orchard grass blades revealed that mesophyll, parenchyma bundle sheath, and parts of the epidermal cell wall apparently were degraded without direct attachment of bacteria although bacteria were near the cell walls undergoing digestion. Anaerobic growth studies showed that the total culturable bacteria developing on medium 10 and media containing carbohydrates similar to those in forage cell walls (i.e., pectin, xylan, and cellobiose) were 80% higher from rumen bacterial populations adapted in vitro to cell walls of orchard grass compared to those from Bermuda grass; the number of colonies from the orchard grass-adapted population was significantly (P less than or equal to 0.05) greater on the medium containing xylan. Filter paper tests showed that the cellulolytic activity of populations adapted to fescue was greater than that of orchard grass or Bermuda grass.     

Antibiosis between ruminal bacteria and ruminal fungi

Cellulose digestion, bacterial numbers, and fungal numbers were monitored over time in vitro by using a purified cellulose medium with and without antibiotics (penicillin and streptomycin). All fermentations were inoculated with a 1:10 dilution of whole rumen contents (WRC). Without antibiotics, cellulose digestion was higher (P < 0.01) at 24, 30, 48, and 72 h; fungi had almost disappeared by 24 h, while bacterial concentrations increased over 100-fold in 24 h and then decreased gradually up to 72 h. In those fermentations with added antibiotics, fungal concentrations increased 4-fold by 30 h and up to 42-fold at 72 h; bacterial concentrations were markedly reduced by 24 h and remained low through 72 h. Similar results were obtained with ground alfalfa as a substrate. In further studies, the in vitro fermentation of purified cellulose without antibiotics was stopped after 18 to 20 h, and the microbial population was killed by autoclaving. Antibiotics were added to half of the tubes, and all tubes were reinoculated with WRC. After 72 h, extensive cellulose digestion had occurred in those tubes without antibiotics, as compared to very low cellulose digestion with added antibiotics. The extent of this inhibition was found to increase in proportion to the length of the initial fermentation period, suggesting the production of a heat-stable inhibitory factor or factors. The inhibitory activity was present in rumen fluid, could be extracted from lyophilized rumen fluid (LRF) with water, and was stable in response to proteolytic enzymes. In addition, the water-extracted residue of LRF was found to contain growth factor activity for rumen fungi in vitro.     

Degradation of cell-wall monosaccharides of chemically treated grape branches by rumen microorganisms

Summary Freshly pruned grape branches were treated with ozone and sodium hydroxide and the effect of treatments on cell wall chemistry and degradability, was studied. Ozonation was expressed in a dissolution of cell wall (CW) components; lignin and matrix carbohydrates were mainly affected and reduced by 44 and 26% respectively. Notwithstanding, the NaOH treatment in creased the proprotion of total cell wall sugars. The distribution of total sugars in untreated grape branches was: 81.5% in CW and 18.5% in cell solubles. The in vitro digestibility by rumen microorganisms of grape branches organic matter, was low (28%) and was increased by, 111% with ozone, whereas NaOH proved ineffective. Ozone increased the in vitro digestibility of CW-glucose by 174%. The possibility of using grape branches as a raw material for conversion to a ruminant feed is discussed.     

Resistance of soil-bound prions to rumen digestion

Before prion uptake and infection can occur in the lower gastrointestinal system, ingested prions are subjected to anaerobic digestion in the rumen of cervids and bovids. The susceptibility of soil-bound prions to rumen digestion has not been evaluated previously. In this study, prions from infectious brain homogenates as well as prions bound to a range of soils and soil minerals were subjected to in vitro rumen digestion, and changes in PrP levels were measured via western blot. Binding to clay appeared to protect noninfectious hamster PrP(c) from complete digestion, while both unbound and soil-bound infectious PrP(Sc) proved highly resistant to rumen digestion. In addition, no change in intracerebral incubation period was observed following active rumen digestion of unbound hamster HY TME prions and HY TME prions bound to a silty clay loam soil. These results demonstrate that both unbound and soil-bound prions readily survive rumen digestion without a reduction in infectivity, further supporting the potential for soil-mediated transmission of chronic wasting disease (CWD) and scrapie in the environment.     

Effect of saponification on the anaerobic digestion of solid fatty residues

In France, fatty residues considered as "non-ultimate" waste will not be accepted in landfill from 2002, in accordance with French legislation. Anaerobic digestion appears as an alternative process to mobilize and profitably use such fermentable waste. In this work, the effect of an alkaline pretreatment on the degradation of hexane extractible matter (HEM) and the production of volatile fatty acids (VFAs) was compared in reactors working at pH 6.5 and 8.5. The results obtained showed that 40% (+/- 0.1) of HEM were degraded at pH 8.5 versus 10% (+/- 0.3) at pH 6.5, regardless of the alkali agent used to saponify the greasy wastes. The highest performances of VFA production (8.45% +/- 0.3) were obtained at pH 8.5 with greases saponified by potassium hydroxide, compared to results (4.25% +/- 0.1) with greasy waste saponified by sodium hydroxide. This difference in VFA production might be attributable to biotoxic molecules generated during the saponification of greases by soda, limiting consequently the VFA production process.     

Antibiosis between Ruminal Bacteria and Ruminal Fungi

Cellulose digestion, bacterial numbers, and fungal numbers were monitored over time in vitro by using a purified cellulose medium with and without antibiotics (penicillin and streptomycin). All fermentations were inoculated with a 1:10 dilution of whole rumen contents (WRC). Without antibiotics, cellulose digestion was higher (P < 0.01) at 24, 30, 48, and 72 h; fungi had almost disappeared by 24 h, while bacterial concentrations increased over 100-fold in 24 h and then decreased gradually up to 72 h. In those fermentations with added antibiotics, fungal concentrations increased 4-fold by 30 h and up to 42-fold at 72 h; bacterial concentrations were markedly reduced by 24 h and remained low through 72 h. Similar results were obtained with ground alfalfa as a substrate. In further studies, the in vitro fermentation of purified cellulose without antibiotics was stopped after 18 to 20 h, and the microbial population was killed by autoclaving. Antibiotics were added to half of the tubes, and all tubes were reinoculated with WRC. After 72 h, extensive cellulose digestion had occurred in those tubes without antibiotics, as compared to very low cellulose digestion with added antibiotics. The extent of this inhibition was found to increase in proportion to the length of the initial fermentation period, suggesting the production of a heat-stable inhibitory factor or factors. The inhibitory activity was present in rumen fluid, could be extracted from lyophilized rumen fluid (LRF) with water, and was stable in response to proteolytic enzymes. In addition, the water-extracted residue of LRF was found to contain growth factor activity for rumen fungi in vitro.     

Effects of isobutyrate on rumen fermentation, urinary excretion of purine derivatives and digestibility in steers

The objective of this study was to evaluate the effects of isobutyrate supplementations on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in steers. Eight ruminally cannulated Simmental steers were used in a replicated 4 x 4 Latin square experiment. On DM basis, diet consisted of 60% corn stover and 40% concentrate. Dry matter intake (averaged 9 kg/d) was restricted to 90% of ad libitum intake. The four treatment groups received a daily dose of 0 (control), 8.4, 16.8 or 25.2 g isobutyrate per steer. With increasing isobutyrate supplementation total VFA concentration (range 64.2-74.0 mM) was significantly enhanced. The ratio of acetate to propionate (range 2.72-4.25) was also significantly increased due to the increase in actate production and decrease in propionate production. With increasing isobutyrate supplementation the ruminal degradation of NDF from corn stover was improved but the CP degradability of soybean meal was decreased. Furthermore, the isobutyrate supplementation caused a significantly increased urinary excretion of purine derivatives. Similarly, digestibilities of OM, NDF and CP in the total tract were significantly increased. The present results indicate that dietary supplementation with isobutyrate improved rumen fermentation and feed digestion in beef cattle in a dose-dependent manner. According to the conditions of this experiment, the optimum daily dose of isobutyrate was about 16.8 g/animal.     

Raw and steam-pelleted cassava,sweet potato and yam cayenensis as starch sources for ruminant and chicken diets

Three tropical tubers, raw or processed by steam-pelleting, were studied in the rumen in vitro or in the chicken in vivo in order to determine the effects of the nature and of the treatment of the tubers on urea utilization by rumen microflora, starch breakdown in the crop and the performance of growing chickens.Starch of cassava (Manihot utilissima) and of sweet potato (Ipomea batata) is characterised by an X-ray diffraction pattern of the A-type and is therefore similar to starch of cereals. In vitro these starches were well broken down in the presence of α-amylase from B. subtilis, and were good sources of energy for rumen microbial growth; in vivo they were completely digested by growing chickens. Compared to cassava, the fermentation of sweet potato in rumen and crop led to increased acidity. The cassava diet gave a better nitrogen retention and growth performance associated with higher food intake.In contrast, starch of yam (Dioscorea cayenensis) which is characterized by an X-ray diffraction pattern of the B-type, and by large granules like potato starch, was less susceptible to α-amylase and promoted lower microbial proteosynthesis in vitro. Starch from a yam diet was more slowly degraded in the crop and its overall digestibility was only 83%. Yam reduced feed intake and gave lower nitrogen retention and lower food conversion ratio and consequently poor growth.The steam-pelleting treatment increased starch availability and permitted better urea utilization by rumen microflora. It improved N retention and feed efficiency of chicken diets, although not significantly. The greatest effect of the treatment was observed with yam.In conclusion, the digestibility of a given starch seems to be related to its structure, characterized by the type of X-ray diffraction pattern, which could be a help in tuber selection for animal nutrition. Simple processing such as steam-pelleting may improve the nutritive value of a tuber, especially when its starch has a B-type crystallinity.     

Use of in vitro gas production models in ruminal kinetics.

Physiological systems models for ruminant animals are used to predict the extent of ruminal carbohydrate digestion, based on rates of intake, digestion, and passage to the lower tract. Digestion of feed carbohydrates is described in these models by a first-order rate constant. Recently, an in vitro gas production technique has been developed to determine the digestion kinetics in batch fermentation, and nonlinear mathematical models have been fitted to the cumulative gas production data from these experiments. In this paper, we present an analysis that converts these gas production models to an effective first-order rate constant that can be used directly in rumen systems models. The analysis considers the digestion of an incremental mass of substrate entering the rumen. The occurrence of passage is represented probabilistically, and integration through time gives the total mass of substrate and total rate of digestion in the rumen. To demonstrate the analysis, several gas production models are fitted to a sample data set for corn silage, and the effective first-order rate constants are calculated. The rate constants for digestion depend on ruminal passage rate, an interaction that arises from the nonlinearity of the gas production models.     

Processing cotton gin trash to enhance in vitro dry matter digestibility in reduced time

Cotton gin trash (CGT) in the raw form is poorly digested by ruminants due to lignocellulosic complexes. These structures must be broken down before adequate digestion can occur. This may be performed by physical and/or chemical means. Two methods for improving digestibility are particle size reduction and/or treatment with sodium hydroxide (NaOH). To evaluate the effectiveness of each method, three experiments were performed in which different CGT types were tested. Each type represented trash from a particular cleaning stage in the cotton ginning process. First, each type was ground with a knife-type grinding mill using screen sizes 0.5, 1.0, and 2.0 mm. For the second experiment, particle size was held constant at 2 mm, and all CGT types were treated with 4% and 6% NaOH (w/w) at room temperature. An agitation cycle of 5 min on and 10 min off was used, with the total mixing time being 4 h. Lastly, particle size and NaOH concentration were held constant, and treatments were performed at room temperature, 40 degrees C, and 50 degrees C. The total mixing times were 2 and 3 h for 50 and 40 degrees C, respectively. For all experiments two subsamples of each treatment were tested for in vitro dry matter digestibility (IVDMD). From grinding alone, digestibility increased as particle size decreased. Grinding to 0.5 mm resulted in an average IVDMD of 47.8% while grinding to 2.0 mm resulted in an average IVDMD of only 33.8%. Digestibility also improved with a greater NaOH concentration. An average in vitro digestibility of 70.5% was achieved with 6% NaOH (w/w) treatment, essentially doubling that of the raw CGT. Increasing the reaction temperature did not result in increased digestibility because the mixture dried out, with a consequent reduction in chemical distribution and uniformity in heat transfer. There are still chemical residues in the CGT, and elimination/reduction of these is an issue that needs to be addressed in further research.     

Rice straw, the role of silica and treatments to improve quality

Rice straw is unique relative to other cereal straws in being low in lignin and high in silica. Unlike other cereal straws taller varieties of rice straws tend to be leafy while the leaves are less digested than stems. This may contribute to higher straw value with rice yield. There is genetic variation in straw quality but has not been exploited and tends to be smaller than environmental variation. Effort in plant breeding has been to develop short varieties with higher grain yield. This development has reduced straw quantity but not nutritive value. The relationship between plant genetics and silica metabolism is virtually uninvestigated, although reviews from plant physiology indicate it is a major factor.

Silica and lignin in that order are the primary limiting factors in rice straw quality. Silicon is a nutrient element which has been overlooked largely because of its assumed inertness, but also because of its geochemical abundance that so greatly exceeds its metabolic use by plants and animals. Silicon is involved in several major roles in rice: carbohydrate synthesis, grain yield, phenolic synthesis and plant cell wall protection. These vectors interact with each other to eliminate statistical association of silica and lignin with straw digestibility when varieties are compared. Yield of grain is highly related to silica content of straw, which reflects soil availability. There are no detailed studies on rice straw lignin. Most papers reporting lignin contents in rice straw have used acid-detergent lignin by either the sulfuric acid or permanganate versions. There are undoubtedly soluble phenolics in rice straw that need investigation. The effects of ammonia and urea on silica is to crack the silicified cuticular layer. Silica is not dissolved by these reagents in contrast to the action of sodium hydroxide.

Treatments on rice straw follow those applied to other lignified materials. In order of frequency of reports, urea followed by ammonia with comparatively fewer papers on sodium hydroxide, steam and pressure treatments or exploded by pressure release, and only one or two papers on acid treatments and white rot fungi. There are reports on animal supplementation and a few growth studies with young animals. Field surveys in India and the southeast Asian countries only report the use of urea, although it appears less efficient than ammonia. Farmer acceptance is related to their perceptions on costs, labor, equipment, health, safety, i.e. the exposure to ammonia vapor, economic and other social factors. The various papers reporting treatments have used animal digestion trials; a variety of in sacco, in vitro digestions with rumen organisms or cellulase, some in combination with pepsin digestion or neutral-detergent extraction. Gas production from in vitro rumen fermentation has also been used. Results are expressed mainly on dry matter basis and fewer reports on organic matter. Results are difficult to compare and standardization of procedures is badly needed. However, most treatments with ammonia and urea show some increase in digestibility and intake where measured in in vivo trials. In vitro and in sacco evaluations tend to overestimate improvement in digestibility.     

Effect of chemical treatments on the degradability of cotton straw by rumen microorganisms and by fungal cellulase

Three different chemical treatments—sulfur dioxide, ozone, and sodium hydroxide—were applied on cotton straw, and the effect on cell-wall degradability was assessed by using rumen microorganism and Trichoderma reesei cellulase. Sulfur dioxide (applied at 70°C for 72 h) did not change the lignin content of cotton straw but reduced the concentration of hemicellulose by 48%. Ozone exerted a dual effect, both on lignin (a 40% reduction) and hemicellulose (a 54% decrease). The treatment with NaOH did not solublize cell-wall components. The in vitro organic matter digestibility with rumen fluid of cotton straw was increased significantly by ozone and SO₂ treatments, by 120% and 50%, respectively, but not by NaOH. T. reesei cellulase was applied on the chemically pretreated cotton straw at a low level (6 filter paper U/g straw, organic matter), and the release of reducing sugars was determined. The highest level of reducing sugars (30.6 g/100 g organic matter) was obtained with the O₃-cellulase combination, which solubilized 64% of the cellulose and 88% of the hemicellulose. the SO₂- and the NaOH-pretreated cotton straw were hydrolyzed by T. reesei cellulase to the same extent (21 g reducing sugars/100 g organic matter). The rumen fluid digestibility of the enzymatic ally hydrolyzed straw was not increased further over the effect already obtained with the chemical pretreatments. However, the fermentability of the combined treatments was increased markedly. In the O₃-cellulase-treated cotton straw, 83% of the rumen fluid digestible material consisted of highly fermentable components. Although ozone proved to be the most potent pretreatment for enzymic saccharification in this study, the absolute result was modest. The limited effect of the combined O₃-cellulase treatment was probably associated with the pretreatment limitations, but not with the enzyme level. Based on the differential response of the chemically treated cotton straw to attack by rumen microorganisms on the one hand, and by T. reesei cellulase on the other hand, a hypothesis has been suggested as to the location of lignin and hemicellulose in the cellwall unit of cotton straw.     

Milk production is unaffected by replacing barley or sodium hydroxide wheat with maize cob silage in rations for dairy cows

Starch is an important energy-providing nutrient for dairy cows that is most commonly provided from cereal grains. However, ruminal fermentation of large amounts of easily degradable starch leads to excessive production and accumulation of volatile fatty acids (VFA). VFA not only play a vital role in the energy metabolism of dairy cows but are also the main cause of ruminal acidosis and depressed feed intake. The aim of the present study was to compare maize cob silage (MCS) as an energy supplement in rations for dairy cows with highly rumen-digestible rolled barley and with sodium hydroxide wheat (SHW), which has a higher proportion of by-pass starch than barley. Two studies were carried out: (1) a production study on 45 Danish Holstein cows and (2) an intensive study to determine digestibilities, rumen fermentation patterns and methane emission using three rumen-cannulated Danish Holstein cows. Both studies were organised as a 3×3 Latin square with three experimental periods and three different mixed rations. The rations consisted of grass-clover silage and maize silage (~60% of dry matter (DM)), rapeseed cake, soybean meal, sugar beet pulp and one of three different cereals as a major energy supplement: MCS, SHW or rolled barley (~25% of DM). When MCS replaced barley or SHW as an energy supplement in the mixed rations, it resulted in a lower dry matter intake; however, the apparent total tract digestibilities of DM, organic matter, NDF, starch and protein were not different between treatments. The energy-corrected milk yield was unaffected by treatment. The fat content of the milk on the MCS ration was not different from the SHW ration, whereas it was higher on the barley ration. The protein content of the milk decreased when MCS was used in the ration compared with barley and SHW. From ruminal VFA patterns and pH measures, it appeared that MCS possessed roughage qualities with respect to rumen environment, while at the same time being sufficiently energy rich to replace barley and SHW as a major energy supplement for milk production. The environmental impact, expressed as methane emissions, was not different when comparing MCS, SHW and barley.