Figure 1. Rice straw nearly stacked. The buffalo will convert it into milk. The same stack of straw would produce more milk if the straw were alkali-treated and supplemented with urea and minerals.
The annual world production of cereal straws and stovers is approximately 2 000 million tons, however, the energy contained in this vast bulk of material is on the whole poorly utilized and its nitrogen incompletely returned to the soil. With the rising prices of both energy and nitrogen fertilizer, interest is developing in more efficient ways of utilizing straws, presently used mainly as livestock feed and as compost material (small amounts are used for the manufacture of paper and fibreboards). In the tropical and subtropical areas of the world almost all straw is fed to livestock, the resulting dung being widely used as fuel. With straw feeding, energy utilization is relatively efficient, except for the residual energy in the indigestible matter which is wasted, but the introduction of dung fermentation in place of dung burning increases the proportion of straw nitrogen which is returned to the soil, thus improving the overall efficiency.
M.G. Jackson is Professor of Animal Nutrition at the G.B. Pant University of Agriculture and Technology, Pantnagar, 263145, India.
In temperate countries the practice of ploughing down straw directly or after using it as bedding returns most of the nitrogen to the soil but wastes all the energy; the same applies to composting, which is done on a large scale in China. Straw burning is practised particularly where crop rotations do not allow sufficient time for ploughed-in straw to decompose, and where livestock enterprises that could use the straw have not been developed. Burning means, of course, a complete waste of organic matter, and this, in addition, pollutes the atmosphere.
Figure 2. Cows eating chaffed rice straw. This is the most efficient way at present recover the energy of straw. Straw nitrogen can also be effectively recovered the dung is subsequently fermented to produce gas.
Improving the efficiency of straw-fed livestock
The utilization of straw through feeding and through the production of gas from the resulting dung is the most efficient system currently available. However, the efficiency of the livestock component could be considerably enhanced by applying presently known techniques, so that more animal products could be obtained from given quantities of straw than at present. The purpose of this article is to describe how this can be done with particular reference to rice straw. Mention will also be made of how rice straw may be used to advantage in intensive systems of livestock production prevalent in those countries where cereals, molasses and oilcakes are available in abundance and rice straw is at present burned or otherwise wasted.
In south and east Asia the rice farmer cultivates at most only a few hectares of land. Tillage operations are done by cattle or buffaloes and the remaining operations by hand, the ripe paddy crop being cut at ground level with sickles and hand threshed. In this process all the straw is recovered, then stored in stacks, which are thatched if necessary, and fed to livestock. To consume the straw obtained from a onehectare crop of rice during the course of a year, one animal is needed; two are needed if two crops are grown. Thus cattle and buffalo populations are high in most of the rice-growing countries of Asia. Animal productivity is low because of the poor nutritive value of rice straw and the very limited amounts of supplementary feeds available. The average availability of cereal and pulse milling offals and oilcakes per head of cattle or buffalo in the rice-growing areas of India is only about 0.1 kg per day; green grass and forage are equally scarce. However, as mentioned above, livestock productivity can be increased, even in the face of limited supplies of supplementary feeds, by the use of urea and mineral supplements and by the alkali treatment of straw.
Nutrient deficiencies of rice straw
Straws are a poor livestock feed, and rice straw is no exception. It contains about 80 percent of substances which are potentially digestible and are therefore sources of energy, but actual digestibility by ruminants is only 45 to 50 percent. Furthermore, the amount an animal can eat is limited to less than 2 percent of body weight because of the slow rate at which it is fermented in the rumen. The net result is an energy intake which provides little or no surplus energy for growth, work or production. The most important consideration in obtaining more animal products from straw in the Asian setting is to improve digestibility and intake so that more energy is available for productive purposes. Protein supplements increase intake, while the alkali treatment of straws increases digestibility and usually voluntary intake as well. The chemistry of straw and its digestion and the chemical changes caused by alkali treatment are receiving increasing attention from animal nutritionists (Jackson, 1977).
Straws contain only 3 to 5 percent crude protein. Animals on an unsupplemented straw diet will usually not gain any weight and very often will actually lose weight. To obtain any production the straw must be supplemented, preferably with both nitrogen/ protein and energy. For good growth on straw diets, a level of 8 to 10 percent protein is needed for young stock; this also improves consumption and thus increases energy intake.
The level of phosphorus in rice straw (0.02 to 0.16 percent) is less than the level of about 0.3 percent that animals need for growth and normal fertility. A level of about 0.4 percent of calcium in the diet is usually considered adequate for livestock, and many samples of rice straw have this amount, the range being from 0.25 to 0.55 percent. Nevertheless, many balance experiments with cattle fed rice straw have shown negative balances of calcium even when the calcium content of the straw was apparently adequate (Nath et al., 1969). While the significance of these negative calcium balances has been questioned (Negi, 1971), the fact remains that in the same experiment higher positive calcium balances have been observed on wheat straw and sorghum stover diets than on rice straw diets, even though the calcium intake on the rice straw diets was higher (Joshi and Talapatra, 1968). It would therefore seem prudent to feed a calcium supplement with rice straw diets.
Sub-optimal cobalt contents in rice straws from Assam and Orissa have been reported (Dube, 1964), and areas of copper deficiency are widespread in India and occur in a number of rice-growing areas. Thus the routine provision of supplements containing at least these two trace minerals would seem to be warranted.
Rice straw differs from other straws in having a higher content of silica (12–16 vs. 3–5 percent) and a lower content of lignin (6–7 vs. 10–12 percent). Whereas in all other straws lignin is the chief cause of low digestibility, in rice straw it is silica. Rice straw stems are more digestible than leaves because their silica content is lower; therefore the paddy crop should be cut as close to the ground as possible if the straw is to be fed to livestock. Thirty percent of rice straw silica is dissolved in the digestive tract, absorbed as silicic acid and excreted in the urine. The concentration of silicic acid in urine far exceeds its solubility limit, and thus it polymerizes into large insoluble molecular aggregates. With some species of grass containing 4–5 percent silica, silicious Urinary calculi are commonly formed in sheep and cattle. Though rice straw contains nearly three times more silica than any of these grasses, urinary calculi are not, in general, a serious problem. When they occur in stock fed rice straw they are probably made up of carbonates and bicarbonates (Talapatra et al., 1948).
Figure 3. A pelleted, alkali spray-treated straw diet. Such diets, containing 50 to 90 percent treated straw, can be designed for a variety of livestock production situations. Pellets are easier and cheaper to transport and store than the straw from which they are made.
Rice straw also differs from other straws in having a high (1–2 percent) content of oxalates. These are broken down in the rumen to carbonates and bicarbonates, absorbed, and then excreted in the urine. The pH of water extracts of rice straw is about 8 and that of urine from stock fed rice straw as high as 9. The high oxalate content has been implicated in the greater need for calcium supplementation (Talapatra et al., 1948). Water washing removes 30–40 percent of the oxalates and substantially reduces urine pH and titratable alkalinity; calcium balance is also improved. Washing also removes adhering soil, which is considerable, but to be weighed against these benefits is the loss of soluble nutrients, equal to about 10 percent of the original weight of straw.
Figure 4. On mechanized farms rice is combine-harvested and the straw is left in the field to be burned.
Urea and mineral supplements
Though rice straw has many limitations as a feed, it is no worse, in general, than other straws. Digestibility determined both in vitro and in vivo is as good as for other straws and in experiments both wheat and rice straw diets, properly supplemented, have equal body weight gains in growing stock.
Cattle fed a diet of rice straw, supplemented in the usual way in the ricegrowing areas of India, grow very slowly (as little as 0.05 to 0.10 kg body weight gain per day) and mature late (4 to 5 years old at first calving). Subsequent fertility is also extremely low, rickets and anaemia are common, and animal production from a one-hectare rice crop is only the draught power needed to cultivate it plus 200 to 300 litres of milk per years. These figures are, of course, average. Farmers with larger land holdings feed more than the average amount of supplements, those with smaller farms less. During the dry season growth may stop or animals may even lose weight, while during the monsoon they gain fairly rapidly because of the green grass and weeds available. An improvement in the nutrition of the small farmers' animals, particularly during the dry season, should thus be the primary objective.
A diet of rice straw alone is not adequate even to maintain animals, which will lose weight if no supplementary protein is given (Table 1). This is true of all straws and roughages containing less than about 4 percent protein, since a level of approximately 6 percent in the diet is needed to prevent weight loss. Alternatively, a supplement of urea at a rate of 1 percent of the straw fed will raise its nitrogen content to a level about equal with the protein supplement. As has been shown in southern Africa with stock on mature veld grass during the dry season (Topps, 1972), this alone can considerably boost animal productivity in terms of time taken to reach maturity and subsequent fertility in females.1
Raleigh and Wallace (1963) obtained good growth responses in cattle when they supplemented mature meadow grass hay containing 5.5 percent protein with 1.6 percent urea.
The need for supplementary calcium and phosphorus has already been indicated; from the results of various experiments about 10 g of supplementary calcium and 5 g of phosphorus would appear to be needed. In areas where specific information on possible trace mineral deficiencies is not available, it would be prudent to give a complete trace mineral supplement; 30 to 50 g of common salt per head/day should also be fed. These mineral supplements will be of use only if a nitrogen/protein supplement is provided.
Figure 5. Farm-scale alkali spray treatment of chaffed rice straw. A 5 percent solution of NaOH is sprinkled on at the rate of 1 litre/kg straw.
1 From the results of these experiments it has been concluded that the feeding of small quantities of cereal or molasses supplements along with urea does not usually give any additional benefit.
Alkali spray treatment
The alkali spray treatment of straws has been shown to improve digestibility and intake (see review by Jackson, 1977). The straw is sprayed or sprinkled with a dilute solution of NaOH at the rate of 1 litre/kg, and the moist straw is immediately fed to animals. The optimum concentration of the NaOH solution appears to be about 5 percent where straw is to be fed with limited supplements, although where treated straw forms only about 50 percent of the diet, 7–8 percent appears to be better. All straws respond about equally to treatment, and an example of the benefits of alkali spraying of wheat straw is given in Table 2. If a smaller volume of a more concentrated alkali solution is applied with a pressure sprayer, the treated straw, along with supplements, may be pelleted. An example of animal performance on pelletted rice straw diets with or without treatment of the straw is given in Table 3.
The grinding and pelletting of poor quality roughages is known to increase intake. Whether the separate effects of alkali treatment and grinding and pelleting are additive has not been established. It seems likely that the high temperature and pressure combination to which treated straw is subjected in the pelleting process enhances the effectiveness of alkali.
The factory-scale processing of rice straw into pelleted complete diets containing 60 to 80 percent straw appears to have good prospects in Asia, where large numbers of milch animals are kept in or near cities and feed is transported from the surrounding country side. Factories for this purpose have already been designed (Rexen and Vestergaard Thomsen, 1976).
The need for a protein supplement with alkali-treated straw requires special comment. Donefer (1968) found that treated straw, when fed without urea, was worse than untreated straw, primarily because intake was severely depressed; on the other hand, a very marked additive effect of treatment and urea was noted. His data are from an intake and digestibility experiment with sheep, whereas only one limited observation on growing cattle is known to have been made so far; Naik (private communication) obtained 0-17 kg live weight gain per head per day with 50 kg calves fed threated rice straw and 1 percent urea. A more efficient use of urea supplement with the treated straw is probably achieved because of the faster rate at which the treated straw is fermented in the rumen.
Figure 6. Rice hand-harvested at ground level to be used as livestock feed.
Rice straw for intensively fed livestock
Even where livestock are kept to convert cereals, molasses, oilcakes and high-quality grass into animal products, straw has a role to play. In experiments in the U.S.A. finishing diets for beef cattle containing 20 percent rice straw and 80 percent concentrates were found to give better results than those containing 100 percent concentrates (White and Reynolds, 1969). The rice straw stimulated intake, and ground rice straw was better than either the long or pelleted forms; fitness of grinding was not important (White, Reynolds and Hembry, 1971). Veitia, Esquivel and Simon (1971) experimented in Brazil with the liquid molasses feeding system developed in Cuba (see Preston, 1972). They fed 2-year-old zebu bulls ad libitum on molasses containing 3 percent urea, rice straw at the rate of 1 percent of body weight, bone meal, salt, and 1 kg of a high-protein concentrate. The bulls gained 0.91 kg/ head/day and were slaughtered at 440 kg.
Terry, Spooner and Osbourn (1975) have shown how alkali spray-treated straw may be used to extend the supply of high-quality grass silage (Table 4). This should have an application in some rice-growing areas as well.
Table 1. - Growth rate of cattle fed urea-supplemented and unsupplemented rice straw
|Crude protein content|
|Drymatter intake (% of body weight)||Drymatter digestibility|
|Body weight gain (kg/day)|
Source: Rekib et al. (1970).
Note: Ten percent molasses was mixed with the straw along with the urea. All animals were given 1 kg of fresh berseem forage daily. Animals weighed 200 kg at the start of the experiment.
In addition to the above, rice straw can be used, with protein and mineral supplements, to carry breeding herds over the dry season. Factory-processed pelleted rice straw diets could be designed to rear beef and dairy calves economically. Treated straw (7–8 kg NaOH/100 kg) could be incorporated in such diets at levels of 50–70 percent.
Feeding livestock appears at present to be the best use to be made of straws. In the tropics the subsequent fermentation of the resulting dung would improve still further the recovery of energy and nitrogen from the straw.
In many of the intensive rice-growing areas of Asia all straw is even now fed to livestock, though it is not efficiently used by them owing to the scarcity of supplementary feeds. Urea, minerals and alkali spray treatment could boost efficiency greatly.
In other parts of Asia, in the Americas, and perhaps in some other areas as well, a large proportion of the rice straw produced is not fed to livestock. The possibilities of feeding it in any of the ways described in this article should be seriously considered, the most appropriate way in any particular situation depending on what other feeds are available and in what quantities.
Table 2. - Animal performance on alkali-spray treated and untreated wheat straw diets
|Untreated straw||Treated straw|
Source: Singh et al. (1975).
Note: The experiment was done on Sahiwal-Jersey crossbred calves weighing 70 kg. Straw was treated with 3.3 kg NaOH/100 kg straw. Groundnut cake was individually fed according to weight.
Table 3. - Animal performance on alkali spray-treated and untreated pelleted rice straw diets
|Untreated straw||Treated straw|
Source: Garret et al. (1976).
Note: The experiment was done on 290-kg steers. Straw contituted 72% of the total diet and was treated with 4 kg NaOH/100 kg straw.
Table 4. - Animal performance on grass silage and a mixture of silage and alkali spray-treated barley straw
|Silage only||Silage straw mixture|
|G DM/kg live weight|
Source: Terry et al. (1975).
Note: The experiment was done on silage with a dry-matter digestibility of 77%. It was mixed with straw in a ratio of 54 to 46 on a dry-matter basis. Straw was treated with 7 kg NaOH 100 kg.
Donefer, E. 1968 Effect of sodium hydroxide treatment on the digestibility and voluntary intake of straw. Proc. 2nd Wld Conf. Anim. Prod., Univ. of Maryland, p. 446.
Dube, J.N. 1964 Cobalt in paddy straw and a related nutritional disorder. J. Indian Soc. Soil Sci., 12: 381.
Garret, W.N., Walker, H.G., Kohler, G.O. & Hart, M.R. 1976 NaOH and NH3 treated rice straw for ruminants. J. Anim. Sci., 43: 322. (Abstract)
Jackson, M.G. 1977 Review article: The alkali treatment of straws. Anim. Feed. Sci. Technol., 2. (In press)
Joshi, D.C. & Talapatra, S.K. 1968 Studies on the utilization of minerals under acid- and alkali-producing cattle feeds. II. Utilization of dicalcium phosphate as influenced by an exclusive feeding of acid-and alkali-producing straws. Indian J. vet. Sci. Anim. Husb., 38: 652.
Nath, K., Sahai, K. & Kehar, N.D. 1969 Effect of water washing, lime treatment and lime and calcium carbonate supplementation on the nutritive value of paddy (oryza sativa) straw. J. Anim. Sci., 28: 383.
Negi, S.S. 1971 Calcium assimilation in relation to metabolism of soluble and insoluble oxalates in the ruminant system: a reappraisal. Indian J. Anim. Sci., 41: 913.
Preston, T.R. 1972 Fattening beef cattle on molasses in the tropics. Wld Anim. Rev. (FAO), (1): 24.
Raleigh, R.J. & Wallace, J.D. 1963 Effect of urea at different N levels on digestibility and on the performance of growing steers fed low quality food meadow hay. J. Anim. Sci., 12: 330.
Rekib, A., Mangate, S., Kochar, A.S. & Bhatia, I.S. 1970 Improvement of the feed value of low-grade roughages by incorporating urea and molasses into them. J. Res., Ludhiana, 7: 347.
Rexen, F. & Vestergaard Thomsen, K. 1976 The effect on digestibility of a new technique for the alkali treatment of straw. Anim. Feed Sci. Technol., 1: 73.
Singh, M. Verma, M.L. Jackson, M.G. & Pitchaiah, K.V. 1976 The effect of alkali spray-treatment of wheat straw on the growth rate of calves. In Improved utilization of agricultural waste materials and industrial by-products as livestock feed. Research Progress Report 1969–74, p. 92. Pantnagar, G.B. Pant University.
Talapatra, S.K. Ray, S.C. & Sen, K.C. 1948 Calcium assimilation of ruminants on oxalate-rich diets. J. agric. Sci., 38: 163.
Terry, R.A., Spooner, M.G. & OsboURN, D.F. 1975 The feeding value of mixtures of alkali-treated straw and grass silage. J. agric. Sci., 84: 373.
Topps, J.H. 1972 Urea or biuret supplements to low-protein grazing in Africa. Wld Anim. Rev. (FAO), (3): 14.
Veitia, J.L. Esquivel, C. & Simon, L. 1971 Elephant grass and rice straw as forage sources for cattle fattened on molasses-based diets. 1. Growth and feed conversion. Revista Cubana de Ciencia agricola, 5: 171. (Nutr. Abstr. Rev., 42: 4402).
White, T.W. & Reynolds, W.L. 1969 Various sources and levels of roughages in steer rations. J. Anim. Sci., 28: 705.
White, T.W., Reynolds, W.L. & Hembry, F.G. Level and form of rice straw in steer rations. J. Anim. Sci., 33: 1365.