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CLOSE THIS BOOKThe Use of Organic Residues in Rural Communities (UNU, 1983, 177 p.)
Discussion I
VIEW THE DOCUMENT(introduction...)
The utilization of agricultural by-products and wastes in Indonesia
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTThe utilization of some agricultural by-products
VIEW THE DOCUMENTThe value of some agricultural by-products
VIEW THE DOCUMENTFuture research objectives
Bioconversion of rice straw into improved fodder for cattle
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTPreliminary treatments
VIEW THE DOCUMENTThe present investigation
The use of fibrous residues in South Asia
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTChemical composition
VIEW THE DOCUMENTMethods of treating cereal straw
VIEW THE DOCUMENTFeeding value of alkali-treated straw
VIEW THE DOCUMENTThe economic feasibility of feeding alkali-treated straw
VIEW THE DOCUMENTPresent use of fibrous residues in India and Sri Lanka
Protein enrichment of starchy substrates by solid-state fermentation
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTTechnical aspects

The Use of Organic Residues in Rural Communities (UNU, 1983, 177 p.)

Discussion I

The importance of agricultural residues as potentially useful feed materials is not in question. There are, however, other factors to be considered in assessing the extent to which this potential could be realized. One is the distribution of the residues. Could small quantities in scattered locations be transported easily or economically enough to justify their processing? It is evident that any method of treating them will have to be within the technical competence of the rural communities, but, to be accepted, it would also need to be in harmony with the social structure.

Certain residues are already being used in Indonesia, as discussed in papers that follow. Processing of residues, particularly microbial processing, can introduce problems of nutritional and toxicological acceptability. No hard and fast rules could be laid down as to how these should be dealt with. Various options are open, and the choice will depend on prevailing circumstances.

The utilization of agricultural by-products and wastes in Indonesia

M. Rangkuti and A. Djajanegara

Animal Husbandry Research Institute, Agency for Agricultural Research and Development, Ministry of Agriculture, Ciawi, Bogor, Indonesia

The utilization of some agricultural by-products
The value of some agricultural by-products
Future research objectives


Crop residues occur fairly generally in the rural areas of Indonesia, but their potential for animal feeding is often not fully exploited. This has important consequences because they form a significant part of the animals' feed. Livestock on the small farm is usually kept for draught purposes or as an investment. In either case, its value is diminished if it is not adequately fed. It is possible to increase the nutritive value of certain of these residues, thus improving livestock productivity.

Research to date has concentrated on determining biological value of residues as they occur rather than on methods of increasing this value. Attempts to improve the nutritional quality of fibrous residues have been confined mainly to physical treatments such as grinding. There is a need to explore and, where possible, apply other methods of treatment if their potential value as animal feed is to be realized more fully.

The utilization of some agricultural by-products

On the basis of a survey carried out in Indonesia on the availability of agricultural by-products to meet the feed requirement of ruminants in particular, measurements were made in some of the islands of the amounts actually used for this purpose. Sampling was carried out at the farmer's level and the supply of any material that was included in the ration was measured. Production was measured during harvest-time at two different periods in a year and then averaged over the year.

The dry matter (DM) production of agricultural by-products that are generally fed to animals is shown in table 1. This is the average DM production of the total available by-products of the plants harvested and left in the field. The main product is not included. Replanting material is also subtracted, hence it could be regarded as the net available DM from one hectare of each agricultural by-product. Their proximate analysis was also carried out on samples taken at harvest and sent to the laboratory. Applying these figures, the total digestible nutrients were calculated and are shown in table 1.

Of the agricultural by-products, corn straw gave the higher yield of total digestible nutrients (TDN) per hectare. The average levels at which the various residues were used in feeds were determined. From these figures the total amounts used were calculated. These were compared with the total quantities produced in the different islands

Although Java is the most densely populated island and the one with the most livestock, not all of the residues produced there are used. One reason for this is that the areas of livestock production do not always coincide with those in which the residues occur. Consequently, while some areas may use all the residues produced and may need even more, other areas may not use their by-products at all.

In the islands outside Java, the distribution of animals within the agricultural system is more even, and agricultural production is also small relative to animal need. There are areas where these by-products are in excess but the animal population is small. The inefficient use of by-products in some areas could be altered to provide a potential supply to other areas where residues are already totally utilized.

TABLE 1. Production and Utilization of Agricultural By-products and Wastes in Indonesia


Production (tons/ha)

Percentage Useda








Other islands

Rice straw








Corn straw








Cassava leaves








Sweet potato leaves








Peanut straw








Soybean straw








a. Values indicate the percentage of the total supply on each island which is put to use.
b. DM = dry matter.
c (TDN) = total digestible nutrients.

The size of any centralized unit designed to increase the nutritive value of residues should be in line with the total availability and continuity of supply of agricultural by-products or wastes.

The value of some agricultural by-products

The nutritive value of agricultural by-products has been measured by various workers. Little or no work has been done to increase their nutritive value by chemical treatment. Chemical composition varied among laboratories and samples. Biological evaluation has been carried out by feeding these materials to animals, usually with the addition of a concentrate supplement. These materials are regarded as low nutritive value feedstuffs, hence the need for the supplementary ration so as to meet the animals' nutritional requirements.

Rice Straw

Rice straw is the main agricultural by-product because rice is the principal staple crop in Indonesia. Rice straw is always available and could be increased in quantity or used more efficiently. The DM and energy content of rice straw is shown in table 1. Its chemical composition varies among samples (table 2), but it is a low-protein, high-fibre material. Sudomo et al. (1) have shown the digestibility of the crude protein of rice straw to be around 30.7 per cent.

The amount of rice straw used in animal rations varies among regions, and Mas Datta et al. (2) have reported up to 58.5 per cent rice straw in daily rations for cattle in the village of Situraja (SumedangWest Java), whereas Sukanto et al. (3) reported the inclusion of the straw at a level of about 37.5 per cent in cattle rations in Playen (Yogjakarta). In Bali rice straw is not generally included in cattle rations. In the rainy season the amount used in feed was only about 2 per cent (4), and even in the dry season its use was not increased. Tahyan et al. have suggested that rice straw could replace up to 25 per cent of "native grass" in feed for sheep (5).

Our results show that buffaloes of 200 kg live weight would consume 15 kg rice straw per day if given ad libitum, but this is not a sufficient intake to meet requirements.

Corn Straw

Corn straw is the second agricultural by-product obtained in rural areas. The yield in DM and (TDN) and the percentage used are shown in table 1. The yields of various components of maize are: grains, 35 per cent; husk and skins, 30 per cent; cobs, 30 per cent; and skin trimmings, 5 per cent. About 6.2 tons of DM per hectare from corn straw are produced during harvest-time. The soft stalks are generally fed to animals, while the tougher parts are composted or burned. The ash is then ploughed into the land. The chemical constituents of corn straw are: cellulose, 40 per cent; pentosans, 25 per cent; and lignin, 35 per cent. It has been used for paper production or to make various types of board.

TABLE 2. Proximate Analysis of Some Agricultural BY-products (Percentage Dry Matter)



Dry Matter

Crude Protein

Crude Fibre

Ether Extract

Nitrogen-Free Extract




Rice straw LPP - 3.93 33.00 0.87 39.77 22.44 - -
Sv - 3.92 26.51 1.95 40.03 22.01 0.42 0.40
Toha - 2.51 46.50 0.55 34.20 18.20 - -
Corn straw Sv - 10.51 29.48 2.94 36.62 13.34 0.38 0.50
Lubis - 3.3 20.20 0.70 31.40 4.4 0.18 0.36
Cassava leaves 20.35 8.95 30.92 1.46 47.93 10.74 0.67 0.36 -
Peanut straw Sv - 13.10 - 2.62 - 20.54 - -
Sugar cane tops 27.92 5.65 35.83 1.44 49.32 7.77 - - -

Corn cobs have short fibres and might be a good feed for ruminants. When cobs are used for fattening cattle, the addition of a suitable concentrate mixture is necessary. With a concentrate mixture of approximately 16.6 per cent crude protein (consisting of fish meal and soybean meal as major protein sources), an average daily gain of 813 9 per head for Onggole cross-breeds and 648 9 per head for Madura cattle was obtained (6). Corn straw fed to cattle with a mixture of urea and molasses could only supply enough nutrients for maintenance.

Cassava Leaves

Few studies on cassava leaves have been made. The young leaves are collected and sold for human consumption, and some are also fed to animals. The stems are generally used as replanting material or, when in excess, as an energy source.

Rice Bran

Large quantities of rice bran are used for livestock feed in all locally produced concentrates at a level of up to 20-25 per cent. Up to 5 kg rice bran per day are also fed to dairy cows, and it is often used for pig and poultry feed. It is estimated that 80 per cent of the total rice bran production is used for animal feeding, leaving 20 per cent for human use.

Sugar Cane

In sugar cane plantation regions, cane tops represent a potential source of forage for ruminants. Such feed has 6 per cent crude protein, 37.4 per cent crude fibre, 41.9 per cent nitrogen-free extract, and 2.4 per cent ether extract with a dry matter content of 29.3 per cent.

Sugar cane tops have been fed to cattle in or near sugar cane regions in Central and East Java, although their biological value was not determined before use. Cane tops increased the feed intake and growth rate of weaned Bali cattle to a greater degree than when the animals were fed elephant grass (Pennisetum purpureum). Feed conversion efficiency was improved in the ration with sugar cane tops (table 3).

Poultry Litter

Until recently, poultry litter has been used in Indonesia as a fertilizer, not as a feed ingredient, though its use in feeds has now started. The litter is composed of poultry manure mixed with feathers, spilt feed, and bedding material that may be chaff, sawdust, chopped straw, or hay. It has the following average compostion: dry matter, 88.3 per cent; crude protein, 14.2 per cent; crude fibre, 20.2 per cent; ether extract, 0:8 per cent; calcium, 11.5 per cent; and phosphorus, 0.54 per cent.

At one time it was feared that the drugs used in poultry feed would inhibit the activity of rumen micro organisms if the litter were fed to cattle, but this does not seem to be so. It has been shown that up to 60 per cent of the concentrate ration of dairy heifers can be replaced by a mixture of poultry litter and rice bran without adverse effects on rate of growth or state of health.

For lactating dairy cows, rice bran could be replaced by poultry litter in an amount equal to 45 per cent of the total intake. This had no adverse effect on the average daily milk yield; however, there was a tendency for milk output to decrease when higher replacement levels were used.


By-products from agriculture are generally used in Indonesia in the state in which they occur, there being little or no attempt made to increase their nutritive value by applying the knowledge already available to do so.

There is a need for more research on the nutritive value of a number of agricultural residues and on methods of increasing the efficiency with which they are used by various types of livestock.

The problem remains in certain areas that the localities in which crops are produced do not coincide with those in which livestock are raised.

TABLE 3. Feed Intake, Feed Conversion Efficiency, and Live-Weight Gain of Weaned Bali Cattle Fed Rations Containing Elephant Grass or Sugar Cane Tops for Four Weeks


Elephant Grass

Sugar Cane Tops

Feed intake (kg/day)


dry matter (DM)



organic master (OM)



Feed conversion efficiency


DM required/leg gain



OM required/kg gain



Live-weight gain, 4-week total (kg)



Source: Lembaga Penelitian Peternakan, Bogor, Indonesia.

Future research objectives

  1. A more detailed knowledge of the composition of organic residues is needed.
  2. The most appropriate methods for increasing their nutritive value for different classes of livestock should be investigated. These may involve physical, chemical, or microbial treatments either singly or in combination.
  3. The methods adopted must be suitable for use by rural communities or individual farmers.
  4. Their effectiveness and limitations must be determined and demonstrated to those who will use them.
  5. If no appropriate method for producing a feed material emerges for a particular residue, consideration should be given to its potential as a substrate for biogas production.
  6. The technologies developed must be transferred to the villages and to the farmer, due regard being paid to the socio-economic problems that will be encountered in doing so.


1. Sudomo et al., "Nilai makanan limbah pertanian untuk ruminansia," Seminar penelitian den hasil penelitian penunjang pengembangan peternakan tradisional (1979).

2. Mas Datta et al., "Kualitas den juantitas ransum tradisional pada peternakan sapi potong," Seminar penelitian den hasil penelitian penunjang pengembangan peternakan tradisional (1979).

3. Sukanto et al., "Status gizi sapi-sapi induk di Playen den Cangkringan, Jogyakarta," Seminar penelitian den hasil penelitian penunjang pengembangan peternakan tradisional (1979).

4. Sudana et al., "Makanan sapi Bali waktu musim hujan," Seminar penelitian den hasil penelitian penunjang pengembangan peternakan tradisional (1979).

5. Tahyan, U., et al., "Pengaruh penggantian rumpus lapangan segar dengan jerami padi kering dalam ransum terhadap pertumbuhan domba," Seminar penelitian den hasil penelitian penunjang pengembangan peternakan tradisional (1979).

6. Rangkuti et al., Bulletin Lembaga Penelitian Peternakan (1973).

7. Toha Sutardi, "Intensitas pencernaan pada kerbau," Proceedings Seminar Ruminansia, Bogor, Indonesia (1978).

Bioconversion of rice straw into improved fodder for cattle

Preliminary treatments
The present investigation

Usha George and T.K. Ghose

Biochemical Engineering Research Centre, Indian Institute of Technology, Hauz Khas, New Delhi, India

The 38.6 million hectares of Indian agricultural land under rice cultivation in 1977 yielded 42.8 million tons of grain (1) and, as by-products, about 81 million tons of agricultural residues - namely, 66 million tons of rice straw and 15 million tons of husks. The cellulosic and hemicellulosic components of these residues (cf. table 1) are potentially available for saccharification or bioconversion to microbial biomass as an improved feed supplement. Research into the use of these residues is being conducted in our laboratory.

In developed countries these residues are disposed of mostly by burning, but now, there being increased interest in recycling these materials that are available in such large amounts, attention is turning toward making better use of them. The traditional uses of rice husks in India have exploited their calorific and abrasive qualities, and they are now being considered for the prediction of good-quality construction materials, while rice straw finds use as fuel, thatch, packing material, and as cattle feed (3; 4).

TABLE 1. Average Composition of Rice Straw and Rice Husk


Composition (%)



Rice strawa

Rice huskb










Crude protein (N x 6.25)




16-17 (silica 83%)

17 (silica 94%)

a. Linko (2).
b. NCST (3).

TABLE 2. Energy and Protein Requirements of Cattle and Availability in Rice Husk and Straw




(Amdult main tenance)


Pregnant cow

Lactating cow

Per/kg rice husk

Per/krrice straw

Digestible energy (x 103 kcal/day) 7.5-12.4 7.5-22.9 10.5-20.6 16.5-49.9 1.2B 1.97
Digestible crude protein (g/day) 110-150 250-410 30-260 240 - 1,660 239 -

a. Adapted from Cuthbertson (6)
b. Ranjhan (5).

Forty-two per cent of the adult cattle in India, employed primarily for draught power, are fed and maintained almost entirely on rice straw; it is also fed to cattle of other age groups with supplements. Quite a number of studies are being carried out in India on the use of other vegetable wastes as feed supolements (5). It is therefore of interest to compare the energy and protein requirements of cattle with the energy and protein available in rice straw (table 2). It is evident that both straw and husk, if untreated or unsupplemented, are not of adequate quality even as maintenance rations. The poor nutritive value results from the resistance of these materials to enzymatic attack by rumen microorganisms. This resistance can be correlated to ( i ) the degree of lignification (7; 8), (ii) the crystallinity of the cellulosic component (9; 10), and (iii) the high silica content (11). In addition, the abrasive quality of rice husks makes ingestion of untreated materials dangerous. Treatment of these materials before feeding to animals is essential.

Preliminary treatments

Non-biological treatments have been used to render straws and other lignocellulosic materials more digestible for cattle (12; 13), or more susceptible to microbial or enzymatic attack (12). Briefly, physical treatments include: (i) size reduction, which increases the surface area of cellulosic and lignocellulosic residues, decreases the crystallinity (14; 15), and therefore increases the susceptibility to chemical action (16) or enzymatic attack (fig.1) (10; 14); ( ii ) moist heat treatment, resulting in thermal hydrolysis and caramelization of sugars (17); (iii) ultraviolet, gamma, or electron irradiation, which lowers the degree of polymerization of cellulose and lignin and partially disrupts the lignocellulosic complex (8). Generally, however, these methods are energyintensive and uneconomical on a large scale.

FIG. 1. Relationship between Lignin Content and In Vitro Digestibility for NaOH-Treated Hardwoods

Chemical treatments, particularly NaOH treatment, have been used successfully (8; 16; 18). These include the use of (i) alkali and (ii) oxidizing agents such as SO2, NaClO2 (or ClO2 ), H2O2, O3, etc. The alkali causes swelling and separation of the cellulose, partial removal of lignin, lowering of the crystallinity of the cellulosic fraction, and partial hydrolysis of the hemicellulose (8; 18). Hot alkali removes a larger portion of the lignin as well as the hemicellulose (Biochemical Engineering Research Centre [BERC], Indian Institute of Technology, Delhi, unpublished data), but such a treatment appears to increase the crystallinity of the cellulose (19). Oxidizing agents act by disruption of bonds in the lignocellulosic complex and within the cellusosic fraction (8).

The present investigation

TABLE 3. Yields of Microbial Protein Derived from Lignocellulosic Materials




Maximum Protein

Yield (%)

Rice straw


Cellulomonas sp. and Alcaligenes faecalis


Paper mill waste fibre


S. pulverulentum


Barley straw


T. reesei




Ch. cellulolyticum




Ch. cellulolyticum


Bleached kraft pulp


Ch. cellulolyticum


Wheat straw


Cochliobolus specifier and other fungi


Rice straw and potato peelings


S. pulverulentum


a. Han (20)
b. Eriksson and Larsson (21).
c. Peitersen (22).
d. Moo-Young et al. (23).
e. Pamment et al, (24).
f. Chalal et al. (25).
g. Ghose, George, and Selvam, unpublished data (BERC, 1979)

Chemical treatment has also been used to render lignocelluiosic materials susceptible to microbial attack (table 3). Work is being done in our laboratory to develop a low-technology process for the conversion of rice straw to improved fodder. It is particularly useful and highly desirable to use such a fodder in Indian villages. A lignocellulosic fungus strain of Sporotrichum pulverulentum, with a well-defined enzymatic capacity (26; 27) and having a favourable amino acid composition of its potential biomass (26; 28), was chosen for this preliminary work.

The effect of mild chemical treatments on protein production of S. pulverulentum grown on rice straw was studied. The treatment and growth conditions are shown in table 4 and the results in table 5. Very poor growth (mostly in the form of spores) and production of protein were observed. Another series of experiments was conducted, therefore, to study the effect of a supplementary carbon source (cane molasses) and slightly different preliminary treatments on protein production by S. pulverulentum. The treatments were similar to those shown in table 4 with some modifications. Instead of the "dry" caustic treatment, as reported by Wilson and Pigden (18), a partially de-lignified straw was prepared by autoclaving 10 9 of straw with 3 9 NaOH in 100 ml of water for one hour. Following the treatments, the caustic or acid was removed by washing until the wash water was neutral. The medium used contained 0.1 g cane molasses, 0.1 9 (NH4)2SO4 per 10 ml distilled water, 2 9 straw, and 10 ml medium in a 250 ml Erlenmeyer flask inoculated for five days at 37 C. Three flasks and one control were used for each treatment. In addition, protein production by an Aspergillus sp. isolated from rice straw was also studied in the same manner. The results are shown in table 6.

TABLE 4. Treatment of Rice Straw and Growth Conditions for Protein Production ( Kjeldahl ) by Sporotrichum pulverulentum









g chemical /100 g straw




Ratio of water to straw





30 C, 24 h

100C, 15 min

100 C, 30 min

pH adjustment



5 % NH3

Final pH

pH 7

pH 7

pH 4.5-5.0



(g/40 ml water/20 g straw)















mycelial fragments of S. pulverulentum


37C, 7 days

a. Wilson and Pigder (18).
b. Han and Callihan (29).

TABLE 5. Effect of Various Treatments of Rice Straw on Protein Production by S. pulverulentum


Mg Protein (N x 6.25)/g Straw










NaOH (spray),0.06 g/g strew



NaOH (100 C), 0.06 g/g straw



H2SO4 (100C), 0.016 g/g straw




TABLE 6. Effect of Treatment of Rice Straw on Protein Production by Aspergillus sp. and S. pulverulentum with Molasses as Supplementary Carbon Source


Mg Protein (N x 6.25)/9

Aspergillus sp.

S. pulverulentum

Uninoculated control

Inoculated straw

Uninoculated control

Inoculated straw

Untreated 35 47 33 58
NaOH (100 C), 0.06 9/9 straw 45 49 36 67
NaOH (120 C), 0.3 9/9 straw 25 39 32 66
H2 SO4 (100 C), 0.016 9/9 straw 36 44 32 64

Aspergillus sp. produced little protein and further studies with this organism were suspended. S. pulverulentum did show a little increase in protein, even in untreated straw. There was little difference in protein production in the straw following different types of preliminary treatments, and not enough increase over untreasted straw was observed to justify the higher cost

Further studies were conducted with untreated straw. The effect of starch and potato peelings or an infusion from potato peelings (10 g peelings, 50 ml distilled water, boiled for 30 minutes) was explored. These experiments were performed in a manner similar to those using molasses, but with the substitution of 0.1 g starch or potato peelings for molasses. In the case of the infusion, 0.1 g (NH4)2SO4 was added to 10 ml infusion and no other carbon source was used. The results are shown in table 7. The results obtained with potato peelings are probably due to the increased nitrogen content and perhaps to the presence of some growth factors.

TABLE 7. Effect of Starch, Potato Peelings, and Potato Peeling Infusion on Protein Production by S. pulverulentum in Rice Straw

Mg Protein/g Straw (Dry)


Uninoculated control


Starch, 0.1 g/g straw



Potato peelings, 0.1 g/g strew



Infusion,a 5ml/g straw



BERC, unpublished data.
a. Prepared by boiling 10 g peelings with 50 ml distilled water for 30 minutes.

The protein yields obtained by certain investigators on lignocellulosic material are shown in table 3. Clearly, our protein yields are lower than those reported by others, but the fact that we have been using simple or no preliminary treatment and much simpler media (25) and yet obtaining enrichment of rice straw appears most encouraging. We have plans to screen several organisms with a view to ascertaining their ability to grow on untreated rice straw either singly or in mixed culture. We are hoping (on the basis of more recent data not reported here) to be able to develop a simple, inexpensive process for the bioconversion of rice straw into improved cattle fodder.


1. India, Ministry of Information and Broadcasting, India: A Reference Manual, 1977-1978 (New Delhi).

2. M. Linko, in Adv. Biochem. Eng., 5: 2511977).

3. NCST, Utilization and Recycling of Agricultural Wastes/By-products: A Country Report (New Delhi, 1974).

4. D.H. Grist, Rice, 5th ed. (Longmans, London, 1975), pp. 432-448.

5. S.K. Ranjhan, Animal Nutrition and Feeding Practices in India (Vikas Publishing House, New Delhi, 1977).

6. D. Cuthhertson, "Nutrient Requirements for Farm Livestock: 2. Ruminants," in D. Cuthbertson, ea., Nutrition of Animals of Agricultural Importance, part 2 (Pergamon Press, Oxford, UK, 1969), Pp. 883920.

7. W.C. Feist, A.J. Baker, and H. Tarkow, in J. Animal Sci., 30: 832 (1970).

8. M.A. Millet, A.J. Baker, and L.D, Slatter, in Biotech. Bioeng., 20: 107 (1978).

9. E.B, Cowling, in Biotech. Bioeng. Symp., 5:163 (1975).

10. T. Sasaki, T. Tanaka, N. Nanbu, Y. Sato, and K. Kainuma, in Biotech. Bioeng., 21: 1031 (1979).

11. P.J. van Soest and L,H.P. Jones, in J. Dairy Sci., 51: 1664 (1968).

12. Y.W. Han, in Adv. Appl. Microbial., 23: 119 (1978).

13. M.G. Jackson, Treating Rice Straw for Animal Feed ( FAO, Rome, 19781.

14. T.K. Ghose and J.A. Kostick, in Adv. Chem. Ser., 95: 415 (1969).

15. J. Nystrom, in Biotech. Bioeng. Symp., 5: 221 (1975).

16. Y.W. Han, W.P. Chen, and T.R. Miles, in Biotech. Bioeng., 20: 567 ( 1978).

17. N. Nesse, J. Wallick, and J,M, Harper, in Biotech, Bioeng., 19: 323 (1977).

18. R.K. Wilson and W.J. Pigden, in Canad. J. Animal Sci., 44: 122 (1966).

19. M. Tanaka, M. Taniguchi, T. Morita, R. Matsuno, and T. Kamibuko, in J Ferment, Technol., 57: 186 (1979).

20. Y.W. Han, in Appl. Microbiol., 29: 510 (1974).

21. K.-E. Eriksson and K. Larsson, in Biotech. Bioeng., 17: 327 (1975).

22. N. Peitersen, in Biotech. Bioeng., 17: 129 (1975).

23. M. Moo-Young et al., in Biotech. Bioeng., 20: 107 (1978).

24. N. Pamment et ah, in Biotech. Bioeng., 20: 1735 (1978).

25. I.D.S, Chalal, M. Moo-Young, and G.S. Dhillon, in Canad. J. Microbiol., 25: 793 (19791.

26. B. von Hofsten, "Cultivation of a Thermotolerant Basidiomycete," in G.G. Birch, K.J. Parker, and J.T. Worgan, eds, Food from Waste (Applied Science Publishers, London, 1976).

27. K-E. Eriksson, in Biotech. Bioeng., 20: 317 (1978).

28. B. von Hofsten and A.L. Ryden, in Biotech. Bioeng., 17: 1183 (1975),

29. Y.W. Han and C.D. Callihan, in Appl. Microbiol., 27: 159 (1974).

The use of fibrous residues in South Asia

M.C.N. Jayasuriya

Department of Animal Husbandry, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka

Chemical composition
Methods of treating cereal straw
Feeding value of alkali-treated straw
The economic feasibility of feeding alkali-treated straw
Present use of fibrous residues in India and Sri Lanka


Crop residues and other agricultural by-products once categorized as wastes have become major components of livestock feed in many Asian countries. The rapid increase in their use has been due to several factors, such as increasing demand for food, greater pressure for agricultural land use, rising cost of better-quality feed, pollution problems due to waste disposal, and the realization of the wasting of enormous quantitites of potential sources of carbohydrates.

With the possibility that world food production may not keep pace with the rapidly expanding population, ruminants in the future will have to use more and more of these fibrous wastes, particularly straws, stovers, and grain mill offals that are available in large quantities.

Of the world annual production of between 2,000 and 3,000 million tons of straws and stovers, Asia produces over 800 million tons, of which about 60 per cent is rice straw, the rest coming from other cereals. Asia produces over 300 million tons of rice straw alone - 90 per cent of the total world production.

India, one of the South Asian countries that uses straw as a major source of roughage for livestock because cultivated green fodder is not available, produces nearly 200 million tons of rice and wheat straw annually. Sri Lanka produces about 2 million tons of rice straw.

Agricultural by-products have many uses in Asia. In Sri Lanka a large proportion of the harvested rice straw is used in the paper industry. In 1978 its two major paper factories used around 47,000 tons of rice straw. Apart from the small quantity of straw used for the feeding and bedding of cattle and buffaloes, most of the straw produced in Sri Lanka is either ploughed in or burned directly on the field. Burning adds a considerable amount of ash to the soil and improves its fertility. Cereal straws are often used for thatching houses in Asian countries. Straw is also a good packing material. Many farmers use straw and stubble as a mulch.

TABLE 1. Chemical Composition of Some Fibrous Residues as Determined by Fibre Analysis Methoda


Cell Content

Well (% of dry) matter)

Hemi- celluloses




Rice straw 21 79 26 33 7 13
Barley straw 19 81 27 44 7b 3c
Wheat straw 20 80 36 39 10 6
Oat straw 27 73 16 41 11b 3c
Sorghum stover 26 74 30 31 11 3
Sugar cane bagasse 18 82 29 40 13 2

a. Method of H,K. Goering and P.J. van Soest, in Forage Fiber Analysis, Agriculture Handbook (US Dept. of Agriculture, Washington, D.C., 1970), cited in Jackson (1).
b. Acid detergent lignin; the other figures in this column are permanganate lignin values.
c. Estimated by subtraction.

Chemical composition

Agricultural by-products are in general poor in nutritive value because of poor and resultant low intake, digestibility although they are used as energy feeds. Cell wall accounts for 70 to 80 per dry matter; cellulose content varies cent of their from 30 to 45 per cent (table 1). The digestible energy intake of such diets is usually not more than 100 kcal/kg livestock on wt0.75 per day, which often is sufficient only for maintenance (1)

Rice straw, the major agricultural by-product of South Asia, is high in lignin and silica. Both these components play an important role in reducing the digestibility of straw. The crude protein content of rice straw is generally between 3 and 5 per cent of the dry matter. Any crop residue with less than 8 per cent crude protein is considered inadequate as a livestock feed because it is unlikely that such residues, without supplementation, could sustain nitrogen balance in an animal. A further deficiency in most fibrous material, especially in rice straw, is the low content of calcium and phosphorus, and probably of trace elements (table 2).

The composition of residues varies with variety, location, and the cultural practices employed in growing the crop from which they are obtained. If the full potential of agricultural residues available in vast quantities throughout Asia is to be realized, it is apparent that some type of treatment before feeding them to livestock should be considered.

TABLE 2. Average Chemical Composition of Rice Straw Compared with That of Alfalfa Hay

  Rice Straw Alfalfa Hay
Digestible energy (kcal/kg) 1.9 2.5
Crude protein (%) 4.5 17.0
Crude fibre (%) 35 0 27.0
Ether extract (%) 1.5 2.0
Lignin (%) 4,5 6.5
Cellulose (%) 34.0 24.0
Nitrogen-free extract (%) 42.0 40.0
Total digestible nutrients (%) 43.0 57.0
Ash (%) 16.5 10.0
Silica (%) 14.0 1.5
Calcium (%) 0.19 1.3
Phosphorus (%) 0.10 0.23
Potassium (%) 1.2 1.50
Magnesium (%) 0.11 0.33
Sulphur (%) 0.10 0.30
Cobalt (mg/kg) 0.05 0.09
Copper (mg/kg) 5.0 14.0
Manganese (mg/kg) 400 30

Source: Clawson et al. (2).

A number of physical, biological, and chemical methods of treatment have been described. Their aim has been to increase digestibility and voluntary consumption, thereby increasing the intake of digestible energy (DE). The treated material is often enriched with nitrogen and mineral supplements in order to make it more complete nutritionally. Some of these methods will be described, the emphasis being placed on chemical methods of treatment. Cereal straws will be considered because they form the major agricultural by-product of South Asia.

Methods of treating cereal straw

Physical Methods

There are two main physical methods of treatment: grinding and pressure-cooking.

Grinding increases the voluntary intake of straw with or without an increase in digestibility, but it often leads to an increase in DE intake. Jackson ( 1 ) quoted an increase of up to 30 per cent in DE by grinding.

Pressure-cooking can increase digestibility, but is generally costly. It may merit further study as an industrial process. Both these physical methods are less effective than alkali treatment.

Soaking of straw in water before feeding is being practiced in many parts of India. It helps to remove soluble oxalate. Though the digestibility of the fibre is depressed, one to two hours of soaking increases voluntary consumption (3).

Biological Methods

Attempts have been made to decompose lignin by microbial and enzymatic means to increase digestibility of lignocellulosic material. Organisms that degrade cellulose and hemicelluloses are of no use, since they deplete the straw of valuable nutrients that the animal itself can digest. Large increases in in vitro digestibility have been recorded by employing white rot fungi, but farm-scale treatment methods have yet to be designed, and feeding trials with animals must be conducted to evaluate the usefulness and practicality of this method of treatment.

Chemical Methods

Attempts to increase the feeding value of poor-quality roughages date back to the early 1900s, when Kellner and Kher in Germany observed that, after sodium sulphite treatment in the paper-making industry, straw pulp was highly digestible (88 per cent) for cattle. Further developments led to the Beckmann method of treatment that had application in Germany for some years beginning in 1921. It is recorded that since the Second World War more than 2 million tons of straw have been treated by this method in Norway alone. Since the early 1960s there has been a revival of interest in straw treatment and several methods of this have been developed. They vary in cost of treatment, effectiveness, and suitability under different conditions.

Many chemicals have been tested, but sodium hydroxide has been found to be the most effective. The effect of sodium hydroxide is to dissolve lignin, silica, and hemicelluloses. Cellulose is not dissolved. The degree of solubilization of cell wall material increases with higher concentrations of the alkali (table 3). Either "wet" or "dry" methods of alkali treatment can be applied to straw.

Wet Methods

TABLE 3. Effect of Varying Levels of Sodium Hydroxide on Cell Wall Material of Wheat Straw (Grams per 100 Grams of Original Untreated Straw Dry Matter)

Treatment (9 NaOH/100 9 straw dry matter)

Cell Wall

Cellulose celluloses




0 74.7 36.3 24.4 7.9 5.2
1 71.7 37.8 21.1 6.7 4.6
2 70.8 36.8 21.6 6.4 4.4
3 69.9 38.0 20.6 5.9 4.2
4 68.1 36.8 18.8 5.7 4.2
6 68.8 38.6 19.2 5.5 4.2
10 66.6 38.9 17.9 5.2 3.7
15 61.9 39.5 12.9 4.8 3.3
25 59.8 38.9 10.8 4.6 3.3

Source: Sharma (4).

Beckmann method. Straw is soaked in 10 or more litres of a 1.5 per cent NaOH solution per kilogram of straw (12-15 kg NaOH/100 kg straw in a volume of 800 1,000 litres of water) and washed in a closed system with extra water after an appropriate period of soaking (18-20 hours). In this way a wet straw is produced with a sodium content of 2 per cent. The method increases the organic matter digestibility by about 20 percentage units for the expenditure of 4-6 kg NaOH/100 kg straw. Straw treated by this method has been fed to livestock on farms in Norway for the past 40 years. One-third to one-half of the total roughage requirement (15-20 kg/day) is given as treated straw. This method, however, has the following disadvantages:

Torgrimsby method (modified Beckmann method). In view of the pollution problem created by the Beckmann method, Torgrimsby in 1971 suggested a closed system in which the amount of water added to the system is equal to the amount of water removed in the treated straw. The method was further developed by Wethje in 1975, and the straw treated by this method is now being evaluated by the Agricultural University of Norway. The easiest way to visualize the Torgrimsby method is to follow the daily sequence on a small-scale farm. Three tanks are needed, each with an attached drain board. Tank A contains 1,000 litres of a 1.5 per cent NaOH solution in which 100 kg of straw, in bundles or bales, are soaked. The first washing tank, B. is twice as long as A and contains 2,000 litres of water. The second washing tank, C, the same size as A, contains 1,000 litres of water.

Step Time Operation
1 07.00 Remove treated straw from A and place on board to drain. This straw was placed in A the day before at 12:00 noon.
2 08.00 Remove drained treated straw from board and place in B. Place fresh (dry) straw (100 kg) in B as well.
3 12.00 Make up NaOH concentration of A by adding 4 kg NaOH. Remove fresh straw from B and place in A. Remove treated straw from B and place on board to drain.
4 13.00 Remove treated straw from board and place in C.
5 16.00 Remove treated straw from C and place on board to drain.
6 17.00 Transfer 300 litres of water from C to B to make up the volume of the latter (100 kg fresh straw removed 300 litres of water earlier).
7 18.00 Wash treated straw on drain board of C with 300 litres of fresh water by pouring over the straw. This runs into C, making up its volume. The treated straw is now ready

Straw treated by the Torgrimsby method has a dry matter content of about 20 per cent and a sodium content of about 2 per cent. In vitro dry matter digestibility is about 70 per cent, an increase of 32 per cent over the untreated digestibility of 38 per cent (5). The method has the following advantages:

It appears to be ideal for small-scale farms in Asia unless field trials prove otherwise.

Dry Methods

Spray treatment. With a view to eliminating the disadvantages of the Beckmann method, Wilson and Pigden (6) evolved a dry process of treatment in which straw is treated with a small volume of concentrated solution of NaOH. The straw is sprayed or sprinkled with the NaOH while being mixed. Research has shown that 4 to 6 kg of NaOH dissolved in 200 litres of water is adequate to wet 100 kg of straw. The quantity of solution required is less (100-120 litres) if a pressure sprayer is used. In a small-scale operation for feeding a few animals, one worker could apply the NaOH solution using a sprinkling can while another turns the straw with a fork. The efficiency of treatment would be less when using a sprinkling can because of poor wetting of straw.

For treating large batches of straw, a screw auger with spray nozzles inside it could be used quite effectively. Another possibility is a horizontal mixer with an overhead spraying device. Both these simple pieces of machinery could be worked either manually or with farm power.

Straw treated in this way is moist and has a pleasant yellow colour and a pleasing odour. Treated straw has a pH of 10 to 11. Animals eat this straw readily, often 20 to 30 per cent more than untreated straw. Digestibility is often increased by 10 to 15 percentage units. Sodium content increases by approximately 0.6 percentage units for every kilogram of NaOH per 100 kg of straw added. When treated with 4 kg NaOH/100 kg straw, the titratable alkalinity is equivalent to 0.5 kg NaOH.

Bulk treatment and stacking. One way to increase the effectiveness of the alkali is to heat the treated straw to a temperature of 80 to 90 C. A practical way of doing this would be to spray the straw with the minimum amount of sodium hydroxide solution and stack the damp, treated straw (10-20 litres per 100 kg straw). If the stack is big enough (3-4 tons), the treated straw will heat up to a temperature of 80 to 90 C. The heating is caused by the chemical reactions between the NaOH and straw. The temperature reaches a peak during the first 3 days and then declines for another 15 days or so to ambient temperature. As a result of heating, moisture evaporates, leaving the straw sufficiently dry for storage. The stack must be made at a well-ventilated site and must not be covered. The initial moisture content of straw should not exceed 17 per cent before treatment.

Though this method looks attractive, it may not be suitable for small-scale farm situations, because a specially designed straw treater is required for the proper penetration of NaOH in a small volume of water (10-20 litres per 100 kg straw). (Such a machine has been produced in Denmark and has shown good results.) The digestibility of straw treated by this method is increased by 10 to 15 percentage units.

Bulk treatment and ensiling. Alkali spray-treated straw can be ensiled satisfactorily for up to one year. There is no microbial fermentation, and the straw remains stable because of its high pH. The optimum requirement of moisture in the final product for satisfactory ensiling may vary according to climatic conditions. Trials in Sri Lanka (Jayasuriya and Somasunderam, 1979, unpublished data) have shown that a moisture content of 55 per cent after treatment is ideal for ensiling treated straw under tropical conditions.

After six months, the treated material (4 per cent w/w) had an in vitro organic matter digestibility of 65 per cent (untreated digestibility 43 per cent). Only about 6 per cent of the straw developed moulds. The pH of the treated straw remained between 9 and 10, and the ensiled straw had a pleasant odour. Trials in the United Kingdom (Owen, personal communication) have shown that 40 per cent moisture in the final product is more suitable for ensiling straw in temperate climates.

Ensiling of straw can also be done with calcium hydroxide. If straw is spray-treated with calcium hydroxide and fed to animals on the same day or the day after, it has little or no effect on digestibility. In fact, we recorded a slight depression in in vitro digestibility with calcium hydroxide, possibly because of its low solubility. Trials have shown that calcium hydroxide can be as effective as NaOH if the treated straw is ensiled for five to six months. This, in fact, could be an answer to achieving a more economical method of straw treatment.

The optimum level of alkali for treating straw has varied from experiment to experiment. It appears that the level of alkali required is different for different roughages, diets, and animals. In general, however, digestibility and voluntary intake increase proportionately up to 3-6 kg NaOH/100 kg straw. In Sri Lanka (7), we found that for paddy straws the optimum level of treatment was around 4 kg/100 kg straw, although there were slight differences among varieties. Evidence also suggests that the optimum level of NaOH may vary with the amount of concentrate supplement given to animals. With high amounts of concentrates in the diet, the digestibility of treated and untreated straw often becomes the same. Under such circumstances, high levels of alkali - e.g., 8 kg/100 kg straw - appear to be beneficial, as the high alkalinity of the straw can counteract the fall of rumen pH and ensure favourable conditions for the activity of cellulolytic micro-organisms.

Ammonia Treatment

Treatment of straw and other roughages with ammonia (gas or solution) has great appeal because (i) it does not leave residual alkali as NaOH, and (ii) it increases the nitrogen content of the material by 0.8 to 1.0 percentage unit.

The standard method of ammonia treatment is not practical under most farm conditions in South Asia. Ammonia should be easily available at low cost with suitable facilities for transport and storage. Furthermore, ammonia application should be carried out by trained personnel.

Methods based on ammonia released from urea have been suggested as suitable for our conditions. One such method is now being evaluated by M.G. Jackson at the College of Agriculture, G.B. Pant University of Agriculture and Technology, in India. Chopped wheat straw is sprayed with a urea solution using a sprinkling can so that the final product has a moisture content of 30 per cent. The treated straw is ensiled immediately. Laboratory trials have shown that after three weeks of ensiling with 4 per cent (w/w) urea, straw digestibility increased by 10 to 12 percentage units (from 53 per cent to 63-65 per cent). An in vivo trial with growing calves is now under way.

Urea treatment seems to increase the dry matter intake by 40 to 50 per cent. The treated material has a pleasing yellow colour and is highly palatable for the animals. The ensiled material has to be exposed to air for one to two hours before feeding to rid it of excess ammonia.

Feeding value of alkali-treated straw

Alkali-treated straw can replace hay and silage in the diet of ruminants if the difference in the protein content between the treated straw and the hay or silage can be made good with an appropriate supplement. In Asia, where straws are widely used as a livestock feed, alkali treatment with supplemental nitrogen and minerals could boost productivity more economically than the feeding of cereal-based concentrate supplements. Results of many experiments have shown the possibilities in this direction.

As early as 1968, Donefer showed the digestible energy intake of sheep could be increased from 84 to 188 kcal/kg wt0.75 by alkali treatment (8 per cent w/w) of oat straw supplemented with 2.5 per cent urea. Many feeding trials in South Asia have clearly indicated that weight gain in growing cattle and buffaloes can be increased by 0.2 to 0.3 kg/day by feeding treated straw supplemented with nitrogen. Trials by Pitchchiah in India have shown that treated straw can effectively extend the limited quantities of high-quality fodder. Our trials (8) have also indicated that, by treatment with 4 per cent (w/w) NaOH, the feed value of rice straw can be made equivalent to that of a medium- to high-quality fodder. The few trials that have been done with milch animals suggest that alkali-treated straw can be successfully incorporated even into the diets of high-yielding cows without altering the milk yield or milk composition. There is much evidence to indicate that, in general, alkali treatment increases the feed value of low-quality roughages.

Urea is an accepted source of non-protein nitrogen (NPN) for ruminants. Feeding trials in Sri Lanka (9) and elsewhere have clearly shown that urea is a suitable source of NPN for supplementing alkalitreated straw. Urea levels up to 2-2.5 per cent of the dietary dry matter have resulted in increased digestibility and greater voluntary consumption of dry matter. Non-traditional industrial by-products high in protein could also play a major role in making alkali-treated straw more complete nutritionally. Spent tea leaf (STL), a by-product of the instant tea industry in Sri Lanka, contains 30 per cent crude protein in the dry matter. Trials have shown that STL (about 7 per cent of the total dry matter intake) can be satisfactorily used as a nitrogen supplement for NaOH-treated rice straw (Jayasuriya, 1979, unpublished data). It appears to be just as good as urea as a source of nitrogen.

High levels of concentrate - levels greater than 30 per cent - should not accompany alkali-treated straw diets. Such levels appear to lower the digestibility of the treated straw, and therefore no benefit can be derived from treating straw used such diets.

The pH of treated straw is generally around 10, and every 1 per cent of the alkali used in the treatment increases the sodium content of the straw by about 0.6 percentage unit on a dry-matter basis. While the animal's body does have mechanisms to deal with high-sodium and high-pH feeds, an intake of high levels of alkali-treated material could lead to a certain degree of physiological stress. At lower levels of treatment (4 per cent and below) the stress is more or less avoided.

Extra sodium ingested is almost entirely excreted in the urine, and blood serum sodium levels are not increased. Milk composition is not affected. Animals often drink more water and excrete larger volumes of urine, but no apparent ill effects have been recorded.

The economic feasibility of feeding alkali-treated straw

Cost analyses have been done on data from many feeding trials conducted in various countries to assess the feasibility of feeding alkali-treated straws to ruminants. It is claimed that in Europe substitution of treated straw for hay or silage may be profitable, especially if the straw has no value other than the cost of collecting it from the field and treating it on the farm.

Trials in India have shown that feeding alkali-treated straw can result in substantial gain in terms of feed cost per kilogram gain in live weight and early maturity of animals (table 4).

TABLE 4. The Effect of Dry Treatment of Wheat Straw on the Performance of Dairy Heifers Fed a Wheat Straw-Berseem Diet


Untreated Straw

Treated Strawa

Dry matter intake (g/kg wt0.75 )



Organic matter digestibility (%)



Live weight gain (kg)



Daily feed cost (Rs/animal)



Feed cost/gain (Rs)



Days to gain 100 kg



Source: Naik and Singh, 1977, cited in Jackson (5).
a. Spray-treated with 9 kg NaOH/100 kg straw.

In Sri Lanka, because of the high cost of NaOH, feeding treated straw under normal conditions may not be profitable. However, during periods of scarcity of good-quality fodder, treated straw could be of considerable value, especially in saving animals from starvation and death.

It is now felt that the rising cost of NaOH may curtail the use of NaOH-treated straw in ruminant diets in many farm situations. Time is now being devoted to a search for cheaper methods of treatment. Ensiling straw with calcium hydroxide and the use of ammonia released by urea have given promising results under experimental conditions. More information is required before these methods can be applied in the field.

Another hindrance in the use of treated straw, as with any new product, is the lack of sufficient information, in physical and economic terms, on the benefit of alkali treatment under real farming conditions at the village level. Animal husbandry in South Asia is more of a family affair in the village; very few large-scale farms are found in these countries. Therefore, the use of treated straw has to be demonstrated with the farmer's animals. Although the economics are favourable, alkali treatment of straw has not been adopted by many farmers in India because it has not been sufficiently demonstrated on farms to convince farmers of its usefulness.

Present use of fibrous residues in India and Sri Lanka

India. The livestock industry in India is mainly geared to produce milk and farm power. Because of the present export policy and high population density, only about 7 per cent of the total cultivated land is devoted to forage crops. Extraction and milling offals are limited in relation to the number of bovine animals. Of the 20 million tons of offal produced annually, about 2 million tons are exported. Thus, the availability of concentrate feed per animal is in the order of 0.2 kg/day. Statistics show that, excluding grazing, dry roughage - mainly wheat and rice straws - constitutes over 50 per cent of the total forage fed to cattle and buffaloes in India (10). This trend will have to continue as higher inputs of high-quality feeds such as forage and concentrate will not be available for future improvement in livestock production. Suitable treatment of straws and other fibrous residues supplemented with nitrogen and minerals will no doubt play an important role in the future of the animal industry in India.

Sri Lanka. Approximately 2 million tons of rice straw are produced annually in Sri Lanka as a by-product of the grain industry. Very little is currently used in the feeding of livestock. Much of the straw is not harvested but is ploughed in or burned directly on the field. Most of the harvested straw (but only 2 to 3 per cent of the total) produced in the northern, central, and southern parts of the island is used in the paper industry. At present it appears to be more profitable to supply the paper industry than to feed livestock, especially when green fodder is available in abundance during rainy seasons. However, with the completion of the diversion scheme of the largest river in the country within the next few years, many uncultivated areas of the country will come under the plough for rice production. This will increase straw production many-fold. Thus, there is a tremendous potential for upgraded straw as a livestock feed in Sri Lanka in the future.


1. M.G. Jackson, "The Alkali Treatment of Straws" (review article), Animal Feed Sci. Technol., 2: 105 (1977).

2. W.J. Clawson, W.N. Garrett, and S. Richards, Microbial Utilization of Straw: A Review (California Agric. Ext. Serv. Publ. MA-1, 1970).

3, M.L. Chaturvedi, U.B. Singh, and S.K. Ranjhan, "Effect of Feeding Water-Soaked and Dry Wheat Straw on Feed Intake, Digestibility of Nutrients, VFA Production in Growing Zebu and Buffalo Calves,"J. Agric. Sci., 80: 393 (1973).

4. S.D. Sharma, "A Study of Roughage Silica Solubility" lM.Sc. thesis, G.B, Pant University, Pantnagar, India, 1974).

5, M.G. Jackson, Treating Straw for Animal Feeding, Animal Production and Health Paper No. 10 (FAO, Rome, 1978).

6. R,K. Wilson and W.J. Pigden, "Effect of NaOH Treatment on the Utilization of Wheat Straw and Poplar Wood by Rumen Microorganisma," Canad. J. Animal Sci., 44: 122(1964).

7. M.C.N. Jayasuriya, "Sodium Hydroxide Treatment of Rice Straw to Improve Its Nutritive Value for Ruminants," Trop. Agric. (Trinidad), 56: 75 (1979).

8. M.C.N. Jayasuriya, "Alkali Treatment of Paddy Straw: Effect of Energy and NPN Supplementation on Digestibility and Intake by Sheep," J. Nat Sci. Council, Sri Lanka, 1 980.

9. M.C.N. Jayasuriya, "Urea as a Source of NPN for Ruminants: 11. Effect of Urea as a Source of NPN on Digestibility and Voluntary Intake of Sheep Fed Alkali-Treated Rice Straw," J. Nat. Sci. Council, Sri Lanka, 1980.

10. V.N. Amble, V.V.R. Murthy, K.V, Sathe, and B.B.P.S. Goel, "Milk Production in Bovines in India and Their Feed Availability," Indian J. Vet Sci. Animal Husb., 35: 221 (1965).

Protein enrichment of starchy substrates by solid-state fermentation

J.C. Senez
Laboratoire de Chimie Bactrienne - CNRS, Marseilles, France

M. Raimbault and F. Deschamps
Centre de Recherche IRCHA, Vert-le-Petit, France

Technical aspects


In spite of current economic constraints, large-scale industrial production of single-cell proteins (SCP) will undoubtedly soon develop in the industrialized countries of Western Europe, Japan, and the USSR, for whom new protein sources are becoming an absolute and urgent necessity. A priori, one would expect the SCP industry to provide a decisive contribution to the problem of hunger in the Third World. In this regard, however, there are several major obstacles.

To be economically viable, an SCP production unit should have a minimal capacity of at least 100,000 tons per year, corresponding to a capital cost of US$50 to 70 million. On the other hand, a plant producing 100,000 tons of SCP from paraffins would require an equal supply of substrate and should thus be associated with an oil refinery having a minimal capacity of about 3 to 5 million tons of crude oil per year. Similar considerations apply to the production of SCP from natural gas or methanol. Such facilities are obviously absent in most non-oil-producing developing countries of Asia, Africa, and Latin America. Moreover, these countries may not have a potential market or an appropriate transportation and distribution network for the commercialization of 100,000 tons of SCP per year.

Clearly, those countries that cannot now import food or feeds because of currency shortage will also not be able to import industrial SCP from abroad. Consequently, it is of utmost importance for them to develop their own protein resources. In addition to hydrocarbons and methanol, a wide variety of raw materials potentially usable for SCP production might be considered. However, most of them are too high in cost to be economically competitive or are available in quantities too low for protein production on a really significant scale. Among the substrates suitable with respect to cost and supply, special emphasis is usually given to cellulosic materials, but, at the moment, the many attempts made in this direction have not been notably successful, the main difficulty being the lack of cellulolytic organisms with an adequate growth rate.

In contrast, starchy materials - more specifically cassava in the tropical regions, or potatoes in more temperate climates - are of obvious interest, both because of their high productivity per hectare, and their excellent rate of conversion to biomass by a great number of fast-growing micro-organisms.

In order to be economically competitive, the production of protein from starch should not be undertaken by classical fermentation in liquid medium, under aseptic conditions, followed by biomass separation and drying. As in the case of SCP production from paraffins and methanol, optimal use of such sophisticated technology would require a minimal production well over the potential market of most developing countries, and would result in high investment and operation costs. Moreover, in the developing countries, the collection, transportation, and storage of large quantities of raw materials would lead to major difficulties.

Given these considerations, a quite different approach is suggested, consisting of protein enrichment of starchy material by a simplified technology that can be applied at the farm or village level, and that will thus simultaneously combine the cultivation of raw material, its conversion into protein, and its direct use for animal feeds. Economically, the decisive advantage of such an integrated approach is that it prevents intermediary profit-taking and speculation that would inevitably develop if either the raw material or the product were commercialized.

To be workable at the rural level, a protein enrichment process should not require aseptic conditions and should be performed in a single operation. Additionally, the final product must be sufficiently rich in protein to be utilizable as such, without a secondary concentration step. This last requisite entails a biotechnological difficulty that has been responsible for the failure of many previous attempts to achieve direct protein enrichment of starchy materials. In a mash of raw material dense enough to be used directly for animal feeding, the major problem is to maintain aerobic conditions and oxygen transfer efficiency so as to prevent anaerobic contamination of the culture.

Tempeh and many other food preparations obtained by solid-state fermentation of soybeans or other materials with filamentous fungi (1-3) are traditionally used in various parts of Asia and Africa, but they do not increase the protein content of the initial materials. On the other hand, procedures for direct protein enrichment of cassava by liquid (4; 5) or solid-state (6) fermentation have been described. However, protein enrichment by the solid technique did not exceed 3 to 4 per cent, and therefore was insufficient for use as a complete feedstuff. The liquid process with fungi presented technical or sanitary problems.

A new procedure for solid-state fermentation (7) fulfilling the above specifications was developed in France. A preliminary report of this technique was presented at the Fifth International Conference on the Global Impacts of Applied Microbiology (81.

Technical aspects

Laboratory Investigations

The principle of this new procedure is based on the homogeneous distribution of spores and mineral salts in the mass of starchy substrate. The preparation of a porous, granulated material with adequate pH, temperature, and moisture content is essential to ensure good aeration and rapid growth of mycelium within the mass.

TABLE 1. Protein Enrichment of Cassava by Solid-State Fermentation

Initial substrate  

Cassava floura









100-120 ml

Optimal growth conditions




Initial pH


Inoculum, spores/g flour

2 x 107

Incubation time

30 hr

Composition of the product



18-20 %

Residual sugarsc

25-30 %


68 %

a. Carbohydrates, 90 per cent; protein, 2 per cent; water 8-9 per cent.
b. Percentage of the dried product, determined by the Lowry method.
c. Percentage of the dried product, determined by enzymatic hydrolysis (lamyloglucosidase) and Somogyi-Nelson titration.
d. Percentage of the wet product.

TABLE 2. Protein Enrichment of Various Raw Materials


Initial Composition

Final Product


Carbo hydrate



Cassava 2.5 90 10 30
Banana 6.4 80 20 25
Banana waste 6.5 72 17 33
Potato 5.0 90 20 35
Potato waste 5.0 65 1 8 28

All results in percentage of the dried material.

Thus, the coarsely ground raw material, with 30 to 35 per cent moisture, is maintained at 70 to 80 for 10 to 15 minutes by gently steaming to gelatinize the starch granules. After cooling to 40 C, the preparation is mixed with water containing the inoculum (spores), the nitrogen sources (ammonium sulphate and urea), and potassium phosphate, to a 55 per cent moisture content. By means of mechanical stirring, the inoculated substrate spontaneously takes the form of well-separated and uniform granules of about 2 to 3 mm in diameter.

General conditions for protein enrichment of cassava or other starchy materials are summarized in table 1. This method has already been worked out with a variety of starchy materials, namely cassava, whole potatoes, potato wastes from industrial fecula works, and banana refuse. The results are reported in table 2, showing that, after 30 hours of incubation, one obtains a product containing an average of 20 per cent true protein, measured by the Lowry methods, and 25 per cent residual reducing sugars. The rate of conversion of carbohydrates to protein is 20 to 25 per cent.

Up to now, experiments have been performed with a selected strain of Aspergillus niger having high amylolytic activity and suitable amino acid composition. However, it should be pointed out that many other filamentous fungi, particularly among strains traditionally used in Asia for producing fermented foods for human consumption, were successfully tested by this technique. This method does not require aseptic conditions, because selective growth of the mould results from acidic pH, low moisture content, and heavy spore inoculation. Microscopic examination of the products indicates that all spores germinate after six to eight hours, and during the growing phase all the mycelia develop. At the end of the fermentation no spores could be observed. Bacteriological controls of fermented products indicate neither pathogens nor significant development of anaerobic bacteria. The aerobic microflora remain at the same level during the first 20 hours, at which time the number of aerobic bacteria quickly decreases.

Experimental Pilot-Scale Studies

The laboratory results led to the design of new equipment for this solid-state fermentation process (9). All the operations were conducted in a commercial bread making blender modified for that purpose.

Steaming or aeration was done by passing steam or air through the perforated bottom of the tank. A control system using conventional probes was designed to keep suitable pH, moisture, and temperature by stirring the product and spraying it with water or mineral solutions. This control system was monitored by a temperature sensor; as soon as the temperature reached the desired point, pH, temperature, and regulation time could be monitored by a simple check of growth rate and harvest-time.

With the organism now used, the optimal temperature is 40 C, but the same growth takes place at temperatures from 30 to 45 C without a significant change in the final protein yield. The initial moisture content is critical, the optimum being 55 per cent. During the course of fermentation, the water content is progressively increased to a final value of 70 to 75 per cent. The kinetics of a fermentation using potato waste are reported in figure 1, showing the production of protein, reducing sugars, and water content as well as the pH of the preparation. The curve marked by crosses is of special interest, since it shows that during a total incubation time of 30 hours the monitored devices for mechanical stirring and spraying had to operate for only five hours, thus demonstrating the excellent efficiency of the cooling device. Additionally, it corresponds to a remarkably low expenditure of power, a fact of obvious importance with regard to the production cost of solid-state fermentation, thus making it economically feasible at the village level in tropical regions.

Currently, the studies on this solid fermentation process are being actively developed in France by the Office de la Recherche Scientifique et Technique Outre-Mer and the Institut National de Recherche Chimique Applique in close collaboration with industry for utilization of potato wastes. The scaling-up of the process to a fermentor unit of 1,200-litre capacity (see photograph) is in progress. This equipment, which is expected to be operative in the coming months, will be used for large-scale nutritional and toxicological testing on target animals (pigs and poultry), for further improvements in substrate preparation and growth conditions, and, finally, for the determination of actual investment and operation costs. It is intended that the experiment will be extended to the setting up of trial production units in tropical Asia and Africa, in order to adapt the procedure to local climatic and agroeconomic conditions.

Agro-economic Perspectives

FIG. 1. Solid-State Fermentation of Potato Waste

As already pointed out, the two main sources of starch potentially available for protein enrichment are cassava in tropical countries and potatoes in temperate climates. Protein enrichment of cassava is of special interest in those semi-arid regions of Latin America and Africa where climatic conditions are not suitable for the cultivation of soybeans or other proteinrich feeds.

The productivity of cassava per hectare varies widely from one region to another, depending on climatic and agro-technological conditions. From about 16 tons (harvested weight) per hectare in north-eastern Brazil, the yield can be easily increased by the use of fertilizers and improved cultivation practices to 40 and even 60 tons per hectare. Other advantages of cassava are low production costs, easy storage in the ground for several months, and high calorie content for animal feeding.

TABLE 3. Agro-economic Prospects of Cassava Compared with Soybeans

Productivity of raw material and protein





Raw material (tons/ha)




Moisture content (%)




Protein (tons/ha)




Conversion into animal product (pigs)d


Alimentary conversion rate




Protein consumption


birth to weaninge


11.3 kg


weaning to slaughterf


25.5 kg




36.8 kg


Overall agro-economic prospects


Ratio of protein productivity per ha of


protein-enriched cassava to soybeans


ca. 3:1


Number of pigs that can be fed with protein


from 1 ha cassava, with solid-state




ca. 50


a. 34 per cent protein.
b. Data from US Department of Agriculture.
c. Based on 20 per cent protein enrichment, with 25 per cent loss of dry matter during fermentation.
d. From ref. 10.
e. 70 days; + 25 kg diet with 15 per cent protein.
f. 130 days; + 85 kg; diet with 10 per cent protein.
g. 200 days; 110 kg.

On the basis of a productivity of 40 tons per hectare and 20 per cent protein enrichment via solid-state fermentation, cassava or potatoes may provide 1.8 tons of protein per hectare, i.e., the supply required for feeding 50 pigs (table 3). This is about three times the quantity of protein per hectare provided by soybean cultivation in the United States. The crop-yield and protein productivity per hectare of other protein sources conventionally used for animal feeding are shown in table 4.

From October 1978 prices and from data on average yields of agricultural products, one can compare the gross product per hectare of corn, wheat, soybeans, and protein-enriched cassava. Actually, in the case of cassava, the value of the residual sugars (35 per cent, dry weight) should increase the gross product figure. On the other hand, for a rural community combining the production of raw material with protein enrichment and direct use for animal feeding, the real gross product should be estimated, not from the commercial value of protein, but from the value of the feedstock produced. Moreover, as already pointed out, one of the major agro-economic advantages of protein-enriched cassava is that it allows feedstock production in regions where no other suitable source of conventional feed protein is available.

TABLE 4. Optimal Productivity of Protein-Rich Feeds


Protein Content


Total Yield (tons/ha)















Horse beans








Protein-enriched cassava




a. 40 tons per hectare of cassava, with 70 per cent moisture content, 25 per cent lost during fermentation, dry weight

Obviously, to be economically competitive, the process of protein enrichment by solid-state fermentation depends ultimately on the investment and production cost of the process. It would be premature to give a truly accurate estimate in this regard until information is obtained from pilot operations at the farm level. However, in the present state of technological development it can be assumed that the process will prove to be valuable.


Protein enrichment of starchy materials destined for direct animal feeding was achieved by a simple, cheap, and non-aseptic process of solid-state fermentation applicable at the farm or village level. The process provides feedstuffs containing up to 20 per cent protein and 35 per cent residual sugars derived from cassava, banana refuse, potatoes, and other substrates potentially available in tropical or temperate climates. On the basis of 40 tons productivity (harvest weight) per hectare, cassava and potatoes could thus provide three times more protein than soybeans and compete favourably with the cultivation of corn, wheat, and soybeans.


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