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Oryza sativaRice straw, paddy strawRice (paddy) straw is produced in large quantities in many countries and serves as a basic roughage for ruminant feeding. It is unique in several ways. The stems are more digestible than the leaves which is the opposite of what is found in other straws. Paddy straw is therefore best for livestock feeding if it is cut as close as possible to the ground. Rice straw contains much more silica (12-16%) and less lignin (6-7%) than other straws (3-5% silica, 10-12% lignin). It also contains high levels of oxalate. 30% of rice straw silica is absorbed and excreted in the urine, yet urinary calculi are not, in general, a serious problem (577). FACTORS AFFECTING NUTRITIVE VALUE As with other straws, nutritive value is variable and influenced by the following factors:
A recent study by Bainton et al. (578) was designed to examine the differences between 5 modern, semi-dwarf varieties and 5 tall, traditional varieties, with 2 levels of N fertilizer (0 v. 90 kg N per ha) and cut in wet and dry seasons. The results are summarized in Table 1. Table 1.
The differences between varieties in feed value were not consistent but the taller varieties produced more nutrients per hectare from their straw. FEED INTAKE OF RICE STRAW Roxas et al. (579) studied the effects of feeding straw from IR36 and IR58 rice cultivars and stubble from IR36 was studied in 2 feeding trials using growing beef cattle (Brahman X native). In trial 1, groups of 4 cattle were fed ad libitum on IR36 straw, IR58 straw or IR36 stubble, for 25 days. Concentrate intake was about 1% of live weight (LW). Daily roughage DM intakes (DMI) were 1.91, 1.62 and 1.98% of LW, differences were not significant. Expressed in relation to metabolic body size (g/kg^0.75), daily roughage DMI were 68.0, 57.8 and 69.8, respectively, differences between straw and stubble from IR36 and straw from IR58 were significant (P < 0.01). In trial 2, groups of 5 cattle were fed ad libitum on straw from IR36 or IR58, for 36 days. DMI was higher (P < 0.05) in IR36 than in IR58 (96.6 vs. 85.6 g/kg^0.75). (These figures represent actual DM intakes of 3.2-4.8 kg per day at 200 kg LW and 4.3-6.5 kg per day at 300 kg live weight.) LUXURY FEEDING Chemical composition of rice straw, as analyzed in the laboratory, may be misleading when applied to field conditions. When straw is available in abundance, the most effective way to utilize straws is to offer approximately twice as much as the animals are expected to consume. This allows the animals to select the more palatable and nutritious parts of the straw, rejecting the remainder which falls to the floor and adds to the bedding. The chemical analysis of the material consumed is likely to be significantly better than that of a random sample of the whole material (E. Owen, personal communication). FEEDING UNTREATED STRAW Untreated straw is commonly fed to draught animals (cattle and buffalo) and mature cows. It is less suitable for young cattle and small ruminants unless it is treated to improve the nutritional value and/or supplemented with suitable energy and protein supplements. Draught animals appear to work and survive on fibrous feeds and are able to tolerate the low digestibility and nitrogen content. NUTRITIONAL LIMITATIONS OF STRAW When straws are fed to ruminants, the primary limitations to production are: - the low overall digestibility - the slow rate of passage due to the rate at which straw particles break down to a size that can leave the rumen - the low propionate fermentation pattern in the rumen - the negligible contents of both fermentable N and bypass protein Reference: 576 TREATMENT OF STRAW The productivity of animals fed straw can be increased by treatment of the straw to increase digestibility and feed intake. Methods include chopping, grinding and chemical treatment with caustic soda, ammonia or urea. Chopping and grinding, while these may increase intake, have little effect on performance and do not change the nutritive value of the straw. Caustic soda, a method used in wartime Europe, is the most effective of the chemical treatments at increasing digestibility but it is not economic and does not contribute to the nitrogen supply. It is also hazardous to humans and animals, results in pollution and is impracticable in most developing countries. There are several ways in which ammonia can be used to increase the digestibility of fibrous feeds, including ammonia gas, ammonia in solution or ammonia generated from urea. Ammoniation of straw appears to be potentially applicable in a wide range of situations. The choice of method depends on cost and availability of ammonia gas relative to urea. Ammonia gas lends itself to large operations where there is the necessary infrastructure for distribution of ammonia in cylinders or tanks. For small farmers, it is more convenient to generate ammonia from urea by the "wet-ensiling process". Urea is a common fertilizer which is often subsidized and which farmers are accustomed to handling. It is no hazard to human health but there is some concern about toxicity of urea to animals. Ammonia is generated rapidly from urea at high temperatures when it is mixed with moist straw, which makes it the system most appropriate for tropical but not temperate countries. A source of urease may also be needed with more inert materials (see SUGAR CANE BAGASSE). The ground seed of Jack Bean (Canavalia ensiformis) is being used for this purpose in Colombia. Urea ensiling appears to be less effective than using ammonia gas because of the formation of ammonium carbonate which decreases the pH of the straw. PRACTICAL METHOD FOR TREATMENT OF STRAW WITH UREA by Frands Dolberg, Novembervej 17, 8210 Aarhus V., Denmark. Of the chemical treatments available, urea treatment has the most relevance to small farmers. Urea is added to the straw at the rate of 5% w/w (air dry basis). The urea is dissolved in water and sprinkled on layers of straw. The quantity of water may range from 0.3-1 litre of water per kg air-dry straw with a minimum being applied in areas with water scarcity. If the straw gets wet with rain or with freshly harvested straw containing much green material, urea can be applied without prior dissolution. Straw can be kept in various ways during treatment. Airtight conditions produce the best results. The conventional method is to use a plastic sheet. A concrete silo, above ground and lined with plastic, will invariably produce good results but concrete and bricks can be difficult and costly to obtain in some circumstances. A construction of earth bricks (clay mixed with straw), as used for making houses of storing grain in parts of Africa, is also suitable. Oil-drums or plastic bags can be used for very small- scale (single animal) quantities. Alternatives can be worked out locally: in dry areas, they can be below-ground pits lined with straw, banana or bamboo leaves or mats; in wetter areas, they can be stacks against a wall or fine meshed wire (chicken wire) containers. When straw is stacked against firm structures (walls, pits, meshed wire), trampling can be done to compact the material and wet straw will not allow air to enter. Even if 100% airtight conditions are not achieved, good results can still be obtained and the outer (untreated) parts can be fed to animals with lower requirements such as draught bullocks or dry cows, while the inner part is fed to growing and lactating animals. Treatment time may vary from 1-4 weeks. In the intensive work undertaken in Bangladesh and Sri Lanka in the early 1980s, 7-10 days was normal, with no benefits in animal performance obtained by longer treatment. However, temperature and treatment time are inversely correlated and more time is required in winter or in colder climates. In well compacted straw, the temperature rises, over 10 degrees C after one week. Simple tests of successful treatment are: brown coloration of the straw, a strong smell of ammonia on opening and the absence of rotten and mouldy straw. ANIMAL PERFORMANCE ON TREATED AND UNTREATED RICE STRAW Chemical treatment of straw increases digestibility and hence boosts animal output. Urea treatment also enables animals to consume more and this is usually considered as an important factor contributing to the increases in output. However, even with intake restricted to the same level as on untreated straw, animal performance in experiments has still been better. There are many experiments reported in the literature. Some examples are shown in tables 2 and 3. Table 2. Effect of urea treatment of rice straw on intake, milk yield and live weight change in Gir cows and Surti buffalo and their calves (Perdok et al., 580) -------------------------------------------------------------------
Table 3. Feed intake, live weight gain and feed conversion with untreated and urea treated rice straw fed ad lib. or restricted. (Khan and Davis, 581) -------------------------------------------------------------------
Supplementation can take the form of green forage, energy and nitrogen sources to encourage optimal rumen conditions and by-pass nutrients (glucogenic and protein feeds). The effect of green forage, such as Gliricidia leaves at 15% of the dry matter intake, has resulted has increased milk yield of buffaloes by 27% (Perdok et al., 580). In Bangladesh, there was a linear increase in milk yield of zebu cows when fish meal was given as a supplement to a basal diet of ammoniated rice straw. Milk yield was increased by 23%, fat percentage by 8% and live weight gain by 110% when 1 kg of coconut cake was fed daily to lactating buffaloes on a basal diet of ammoniated rice straw and minerals in Sri Lanka. Wanapat et al. (584), in an experiment with young (150 kg) Brahman bulls fed ammoniated rice straw supplemented with 0.9, 1.7 and 2.6 kg of a supplement (66% rice bran, 22% broken rice, 11% soya bean meal, plus minerals and salt), obtained live weight gains of 0.43, 0.84 and 0.93 kg/day respectively. MOLASSES-UREA BLOCKS The use of multi-nutrient blocks has allowed for a substantial reduction in concentrate in the diet of buffalo cows fed on rice straw. The fat corrected milk yield was not diminished by replacing part of the concentrate with block. But the amount of straw in the diet and thus the profit per animal per day were greatly increased. Compared to urea supplied by spraying on straw, urea from blocks give superior results. It is assumed that part of the response may be due to the small amount of supplementary energy supplied by the molasses but also by a stimulatory effect of other ingredients in the blocks on the rumen ecosystem (Ref: 576). For further details see MOLASSES-UREA BLOCKS. MINERAL SUPPLEMENTATION The mineral content of straws is generally low and imbalanced but deficiencies are unlikely to be manifested in animals at maintenance or working. For production of meat and milk, requirements for minerals are increased many fold and supplements should be supplied. However, responses to mineral supplements will only occur after major nutrient imbalances (protein and glucogenic energy) have been corrected. Calcium and phosphorus contents of straw are usually below recommended levels and cobalt, copper, sulphur and sodium may also be deficient. The high content of oxalates and silicates in rice straw also suggest that considerable amounts of calcium and magnesium salts can be lost as silicates and oxalates in urine and faeces. (Ref. 276) LIMITATIONS ON CHEMICAL ANALYSIS ON STRAWS (Uden, 582) The ability of ruminants to digest various plant fractions differs. Using the detergent system of analysis, plant material can be divided into a highly digestible, an indigestible and a fraction of varying digestibility. The proximate analysis system fails in this respect. Lignin is the most important plant component which restricts fibre digestibility. Silica, cutin and tannins also restrict fibre digestibility in certain plants. Cellulose crystallinity and minor constituents such as acetyl groups and phenolic acids are less well understood. Chemical analysis of specific plant fractions is generally less reliable for predicting digestibility but can give important information as to what limits digestion. Near infrared reflectance spectrophotometry is useful for large scale analyses but requires calibrations with sets of reference samples of known digestibilities, some knowledge of botanical composition and large capital investments. Biological methods (in vitro, nylon bag and cellulase methods) are generally the most reliable methods. Chemical analysis of treated straw is even more difficult and may bear little relation to the change in animal performance. Analysis of ADF nitrogen is probably the most appropriate method of measuring unavailable N in ammoniated straws. The remaining nitrogen is available for use by the rumen microorganisms. Generally, chemical analysis data is a poor indication of the value of both untreated and treated straw - animal intake and performance give much better guides. This is particularly true of the luxury feeding situation (see above) in which the animals are allowed to select the better parts of the material. PROXIMATE ANALYSIS
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