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Department of Animal Husbandry, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka
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||Cell Wall (% of dry matter)||Hemi- celluloses||Cellulose||Lignin||Silica|
|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.
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|
|Nitrogen-free extract (%)||42.0||40.0|
|Total digestible nutrients (%)||43.0||57.0|
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.