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Rice straw is a fibrous by-product from rice production industry that has not been fully recognized and utilized as ruminant feed in Malaysia. Rice straw is still abundant and considered as an important feed resource, but has yet to find significant uses for the production of ruminant. Instead, post-harvest open burning of straw becomes a common and wasteful farming practice during the harvest season and creates environmental concerns.
Like other typical fibrous cereal straws, rice straw is largely characterized by poor nutritive values associated with high contents of indigestible cellular components such as detergent fiber and lignin while being relatively low in crude protein (Jackson, 1978). These inherent properties of cereal straw result in its low digestibility, poor intake and the animal's growth response.
Enhancing the digestibility of straws is an important step for an efficient utilization of straw by the ruminants. Improved digestibility in the rumen is achieved by providing the rumen with the nutrients poorly supplied by the ingested straw or by improving the digestibility of the straw itself.
For the purpose of improving the digestibility of the straw, many strategies have been developed. The straw could be treated with chemical, physical, microbiological, or combinations of means. Chemical treatment appears the most common and effective way particularly by using sodium hydroxide and urea-ammonia (Carmona & Greenhalgh, 1972; Wilson & Pigden, 1964; Jackson, 1977). Chemical methods could be economically not feasible at small farm level, but is a suitable approach in industrial scale of farming. However, chemicals could be hazardous to the animals and farm hands.
Straw mushroom (Volvariella volvacea) naturally grows well on decaying rice straw. Straw mushroom ecologically is saprotrophic which feeds on decaying organic matter. The roots of the straw mushroom, called mycelium, will penetrate the lignified cell wall of the rice straw. The process of breakage of the cell wall will increase the digestibility of the straw. In addition, the straw mushroom is also high in protein which later might increase the protein content of the treated rice straw.
Growing of the mushroom using straw as media is a form of treatment of the straw. It is an economical method as compared with other methods while benefitting from the production of edible mushroom. The spent straw (media) could then be effectively utilized by the ruminants as studies have shown the beneficial effect of mushroom on the digestibility of the straw (Streeter et al., 1982; Das, 1983). The strategy of using this spent straw would enhance the utilization of rice straw for feeding ruminants.
Treated rice straw with Volvariella volvacea can be an alternative feed of forages for ruminants and might contribute to crude protein content in the ruminants feed ration thus may reduce the total feed cost. Malaysian ruminant industry in particular will be given another feed resource in her strategy to improve productivity and profitability of farming ruminant as a business.
The objectives of this study were:
To evaluate the nutritive contents (DM, ADF, NDF, ADL and CP) of the rice straws treated with Volvariella volvacea and the untreated rice straws.
To evaluate the fiber digestibility of the treated and untreated rice straws with Volvariella volvacea.
The rice straw based media from the production of straw mushroom has higher nutritive values (nutrient contents and digestibility) than the rice straw media that has not been utilized for the cultivation of the mushroom, Volvariella volvacea.
2.1. Rice straws
2.1.1 Nutritive values of rice straw
Rice produces the largest amount of crop residues despite it is the world's second largest cereal crop after wheat (Encyclopedia Britannica). Rice straw is known for its low in digestibility and protein. The relative compositions and digestibility of rice straw compared with barley, oats and wheat straw are shown in Table 1. From the table, rice straw contains low in lignin and high in silica as compared to other straws.
Composition and digestibility of rice and barley and wheat straws a
a Compiled from Doyle and Panday (1990), Jones and Handreck (1967), National Research Council (1982), Van Soest, 1970 and Van Soest, 1994.
Lignin is likely the second most limiting factor to rice straw quality after silica. There is 2 ways to evaluate lignin content in rice straws; acid-detergent sulphuric acid lignin and acid-detergent permanganate lignin. There were no direct comparisons between acid-detergent sulphuric acid lignin and acid-detergent permanganate lignin. The two acid-detergent lignin procedures probably do not give the same values on rice straws, the sulphuric acid method tending to be somewhat higher than that of the permanganate. The reason is the interference of the silica. Silicic acid does not lose all of its water up to about 800 Â°C (Van Soest and Robertson, 1985). The difference in weight loss between 100 and 500 Â°C is significant, so that the ADL method credits the loss of water from the silica to the lignin estimate. This error is small in forages that do not have much silica. However, in the case of rice straw it becomes a concern.
2.1.3 Treatments to improve quality
There is various of chemical and biological treatments to improve straw have been employed, involving sodium hydroxide (NaOH), ammonia, urea, pressure and heat in combinations with steam, pressure and ammonia, urine, enzymes, acids and fungi. The Beckman method, which is the oldest treatment, is to soak straw in solutions of NaOH, drain and wash. The result dramatically increased digestibility. However, there is considerable loss in dry matter including valuable soluble organic matter. Attempts to increase the recovery of nutrients resorted to spraying NaOH solutions onto the straw and allowing to dry. This forces the animal to consume the added alkali inducing heavy urination, and faster rumen washout.
The large increase in digestibility seen in in vitro measurements may not be realized in animal digestion trials for several possible reasons. NaOH cleaves the lignin bond and increases the disintegration of the fibre reducing particle size and increasing passage of undigested fibre (Klopfenstein, 1978). Also intake of soluble sodium salts increases osmotic pressure and rumen washout (Jackson, 1977). For rice straw, the presence of soluble silica in the rumen is also a potential source of inhibition of cellulolytic digestion (Shimojo and Goto, 1989 and Smith and Urquhart, 1975).
2.2. Volvariealla volvacea
Volvariealla volvacea commonly known as the straw mushroom, paddy straw mushroom or the Chinese mushroom (Chang, 1972). It is an edible mushroom of the tropics and subtropics, and it began to be cultivated in China as early as 1822 (Chang, 1972a). Around 1932 to 1935, V. volvacea has been introduced into the Philippines, Malaysia and other Southeast Asian countries by overseas Chinese (Chang, 1974). An outline of the classification of V. volvacea is as follows (Singer, 1975):
V. volvacea is referred to as a "warm mushroom" because it can grow at relatively high temperature (32 - 40 â°C) and high relative humidity (80 - 90 %). It is a fast-growing mushroom; the time required from spawning to harvesting is only about 8 to 10 days. However, the ability of its mycelium to become colonized with its substrate is rather weak.
V. volvacea can use cellulose materials more effectively than other cultivated mushroom. It can grow quickly and easily in uncomposted substrates such as paddy straw. All mushrooms use lignocelluloses as a substrate. Lignocellulose is often divided into 2 macromolecular groups, lignin and cellulose. In addition, there is hemicelluloses which is more variable in structure, but also more easily metabolized. Not all lignocellulose is equally useful to every mushroom species. V. volvacea prefers high cellulose, low lignin-containing substrates.
MATERIALS AND METHODS
3.1. Experiment I: Rice straw treatment with Volvariella volvacea
The experiment was conducted at the Mushroom House, Taman Pertanian Universiti and Nutrition Laboratory of the Department of Animal Science, Faculty of Agriculture, University Putra of Malaysia.
3.1.2 Volvariella volvacea spawn
The V. volvacea spawns were supplied from Modern Farmer Agroresources Sendirian Berhad. The spawn was prepared on wet, chopped rice straws under aseptic conditions. 2-month-old straw spawns were used for all culturing experiments.
Plate 1: 2-month-old V. volvacea spawn
3.1.3 Rice straw
The rice straws were taken from paddy fields in Tanjung Karang, Selangor, Malaysia and were field dried in small round bale form.
3.1.4 Method of cultivation
The harvested rice straws were divided into 3 groups; untreated rice straw (URS), control (C) and treated straw (TS). The V. volvacea was cultivated indoor in the Mushroom House, Taman Pertanian Universiti, University Putra of Malaysia. Samples of URS were taken to evaluate the initial nutrient content which was then compared to the nutrient content of C and TS. The remaining rice straws were soaked for 2 hours in a plastic water tank filled with tap water. The mushroom beds were made in perforated plastic baskets (11cm x 14cm x 9cm) where the straws were rolled into cylindrical shape parallel with the length of the basket. The rice straws were arranged tightly and compacted to ensure maximum contact for mycelium growth. The excess water was drained before spawning. Any protruding and dangling rice straws were cut.
The V. volvacea spawns were distributed on the surface of the rice straws bedding. 9 pieces of the thumb-size spawn were equally distributed and were buried 5 cm deep in the rice straws bed. The surface was massaged to close the open spaces as a result of spawn insertion.
Both C and TS groups had 15 replicates. The treatments and replicates were randomly assigned to each of the baskets and labeled. The spawned rice straw bedding in the plastic baskets were placed on 2 wooden racks inside the mushroom house. The 3 tiers wooden racks are covered entirely with plastic sheet. The purpose of wrapping the racks with plastic sheet was to elevate the temperature and maintaining the high moisture that was required for the V. volvacea to grow. The temperatures inside the wrapped racks were maintained at 31Â±5 Â°C and relative humidity of 75-85%. The temperature and relative humidity were monitored by using a digital hygrometer (Pro'sKitÂ® MT-4014). The method of elevating the temperature and moisture was using a heater coil in a pail of water. Spraying with a superfine mist was also used to help maintaining the desired relative humidity when the rice straws bedding appears to be getting dry.
Plate 2: Tightly rolled cylindrical shaped rice straws in the perforated plastic basket
Plate 3: Perforated plastic basket containing 3 rolls of cylindrical shaped rice straws
Plate 4: The wooden racks used
Plate 5: The wooden racks wrapped with plastic sheet sealed with cellophane tape
3.1.5 Experimental design and rice straw treatment
The studies were conducted using a Complete Randomised Design (CRD). 15 samples (replicates) were taken from the rice straw bales to evaluate the initial nutrient contents of the rice straws (T1). Both T2 and T3 which had 15 replicates each were placed inside the wrapped wooden racks for 15 days. The treatments of the rice straws were shown in Table 2.
Rice straw treatments for experiment I
Untreated rice straw samples taken from the bale
Rice straws without
Rice straws treated with V. volvacea
3.1.6 Harvesting and spent rice straw sample collection
The fruiting body of V. volvacea was not left to grow to their maximum size and they were picked before the volva breaks (egg-like shape) or just after rupture. The first crop of mushrooms harvested 10 to 15 days after spawning. The samples of spent rice straws left after harvesting were taken on the 15th day.
The spent rice straw samples were taken at the site where the fruiting body of the V. volvacea grew. The fruiting bodies were removed from the spent rice straws and only the spent rice straws were taken as sample. All of the sample were placed into plastic zipper bags and brought to the nutrition lab for oven drying at 60Â°C until constant weight. The spent rice straw samples were then grounded to 2 mm size and were kept in vials, capped and labeled for use in the analysis.
Plate 6: The egg-like shape of the fruiting bodies of V. volvacea on the rice straw bed
Plate 7: Different stages of development of the straw mushroom, V. volvacea (from left: "button", "egg", "ruptured", "elongation" and "mature")
3.1.7 Analytical methods
Chemical analysis were conducted on the samples to determine the content of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) in the rice straw samples. The procedure and technique used for DM and CP were according to Association of Official Analytical Chemists (A.O.A.C, 1990) while NDF, ADF and ADL were determined by the method according to Van Soest et a.l (1991).
3.1.8 Statistical analysis
The data for the different parameters were analysed by using SAS (2002) statistical program by one-way analysis of variance (ANOVA) method. Treatments of all means were compared. Significance between individual means was identified using Duncan's multiple range test. Mean differences was considered significant at P< 0.005.
3.2 Experiment II: In vivo digestibility of the rice straws
3.2.1 Animal and management
Three males of Saanen goats with average body weight of 30 Â± 5 kg and at 4 years of age were used in this experiment. The goats were fitted with permanent rumen cannula to evaluate the digestibility of DM, NDF, ADF and ADL at 24 hours. All goats were de-wormed and placed in individual pens.
3.2.2 Experimental design
The experiment was conducted in randomized complete block design with 3 treatments (URS, C and TS) and goat as the blocks (goat 1, goat 2, and goat 3). Each treatment had 5 replicates. The apparent digestibility study was conducted for 24 hours. A total of five nylon bags were incubated in the rumen of each goat.
Approximately 5 g of rice straws was weighed into nylon bag of size 10-20cm with 40 micron pore size. The nylon bags were tied with raffia strings. 15 nylon bags containing samples from URS, C and TS respectively were randomly assigned to each goat.
The nylon bags were incubated in the rumen by suspending the bags through the attached cannula of the goat. All 5 bags from each goat were withdrawn at 24 hours post-incubation. The bags were then well-washed with running tap water. The nylon bags were dried in the oven at 60oC for 24 hours and the weight was recorded.
3.2.3 Analytical methods
Samples of the rice straws were analysed for DM, NDF, ADF and ADL. DM content was determined by drying the samples at 105â°C overnight (A.O.A.C, 1990). NDF, ADF and ADL contents were determined by the method according to Van Soest et a.l (1991).
3.2.4 Statistical analysis
The data for the different parameters were analysed by using SAS (2002) statistical program by one-way analysis of variance (ANOVA) method. Treatments of all means were compared. Significance between individual means was identified using Duncan's multiple range test. Mean differences were considered significant at P< 0.05.
RESULTS AND DISCUSSION
4.1 Experiment I: Rice straws treatment with Volvariella volvacea
The chemical compositions of the untreated rice straws (URS), Control (C) and treated rice straws (TRS) are shown in Table 3. Both C and TRS have significantly (P<0.05) lower DM than the URS. The differences are due to the V. volvacea which has utilized about 3% DM of the rice straws for the formation of the mycelium and the fruiting bodies during the experiment.
The NDF in TRS is significantly (P<0.05) lower than the URS. The NDF value represents the total cell wall that comprises of the ADF fraction plus hemicelluloses. The V. volvacea has been shown to utilise hemicelluloses better than celluloses and lignin (Chang-Ho and Yee, 1977). However, the ADF in TRS has increase significantly (P<0.05). The increase in ADF in TRS is possibly caused by the addition of cell wall content from the V. volvacea mycelium. Like the other fungi, the cell wall of the V. volvacea is mainly constituted with chitin which is a polymer of N-acetylglucosamine (Chang, 1964). These units form covalent Î²-1,4 linkages similar to the linkages between glucose units forming cellulose (Heppe Medical Chitosan, 2009). Chitin may therefore be described as cellulose with one hydroxyl group on each monomer substituted with an acetyl amine group (Great Vista Chemicals, 2008). The increase in cellulose content in the TRS is the reason of the significant increase in the ADF.
The significant (P<0.05) decrease in ADL in TRS further convince us that the increase in ADF is resulted by the addition of cellulose content by the mycelium cell wall. The ADL in C and URS are about the same. The significant (P<0.05) decrease of ADL in TRS indicates the lignolytic behaviour of the V. volvacea.
Due to the growth of V. volvacea, the CP content in TRS has decreases significantly (P<0.05). This may be due to the uptake of nitrogen in the TRS by the V. volvacea for the formation of the chitin for the cell wall of the mycelium and the fruiting body of V. volvacea. As stated earlier, chitin is a modified polysaccharide containing nitrogen which it is synthesized from the units of N-acetylglucosamine (MeSH, 2009).
Figure 1: Structure of cellulose
(Source: www.scientificpsychic.com/fitness/carbohydrates2.html, 2005)
Figure 2: Structure of chitin
(Source: www.scientificpsychic.com/fitness/carbohydrates2.html, 2005)
Untreated rice straws, control and treated rice straws after cultivation of
a,b Different letters in columns indicate significant differences (P<0.05).
1 URS = Untreated rice straws.
2 C = Control.
3 TRS = Treated rice straws.
4 Mean values.
5 Standard deviation.
4.2 Experiment II: In vivo digestibility of the rice straws
The apparent digestibilities of the materials in goats are presented in the Table 4 and Table 5, based on the different components of the rice straws. The digestibility of CP is not included. The apparent digestibility of DM, ADF and NDF in TRS increase by 17, 7 and 3 %, respectively as compared with the URS. The increase in the digestibility of the DM, ADF and NDF in TRS can be considered a consequence of the increase availability of these materials to bacterial enzyme reactions in the rumen due to fungal attack on the cell walls of the rice straws during the growing of V. volvacea. However, there is no improvement in the digestibility of ADL in both C and TRS as compared with the URS. The increase in apparent digestibility in DM and ADF of C as compared with the URS may be due to the soaking of the straws in tap water for 2 hours which is the pre-treatment before the rice straw bedding is made. Since the C is also kept in the high moisture and temperature environment along with the TRS for 15 days, some bleaching may occur; weakening of the cell walls integrity (Chang-Ho and Yee, 1977).
In vivo digestibility coefficient in goats (%)
Dry matter (DM)
Neutral detergent fibre (NDF)
Acid detergent fibre (ADF)
Acid detergent lignin (ADL)
a,b,c Different letters in rows indicate significant differences (P<0.05).
In vivo digestibility coefficient in goats (g/kg)
a,b,c Different letters in columns indicate significant differences (P<0.05).
1 URS = Untreated rice straws.
2 C = Control.
3 TRS = Treated rice straws.
4 Mean values.
5 Standard deviation.
This study was conducted to evaluate the nutritive value and digestibility of spent rice straws after been treated with Volvariella volvacea. The nutritive value of TRS was compared to the URS, which contained the initial nutritive values of the rice straw. From the nutritive value experiment, it was found that the V. volvacea treatment had significantly (P<0.05) lowered the NDF and ADL contents of TRS. However, there was a significant (P<0.05) increase in ADF content of TRS due to the addition of the V. volvacea mycelium cell walls. The CP content of TRS was significantly (P<0.05) decreased. As in the second experiment (digestibility of the rice straws), the V. volvacea treatment had significantly (P<0.05) increased the apparent digestibility of DM, ADF and NDF of TRS by 17, 7 and 3 % respectively. However the difference in the apparent digestibility of ADL in TRS was not statistically significant.
The spent rice straws from the production of V. volvacea had the potential to be utilised as an alternative feed for ruminants. This could reduce the feed cost as the rice straws were abundant and readily available during the harvesting season in Malaysia. Considering the reduced protein content of the spent rice straws, protein supplement should be included in the ration when feeding the spent rice straws to the ruminants.