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Citation of this paper
Rice straw is the most abundant agricultural-byproduct in Asian countries, but its utilization as animal feed is poor. The main constraint to increasing its utilization as animal feed is the poor intake and digestibility as caused by the low crude protein contents and high lignification and silicification of cell wall. One cheap and practical way to overcome the problems is through fermentation with urea. To generate information about chemical composition and nutritive value of of urea treated rice straw as animal feed, literatures in Google Scholar, CAB Abstracts, Web of Science, PubMed and Scopus were searched. From those databases, nutritional composition and nutritive value of untreated and urea treated rice straw are elaborated and reviewed. Means of improving animal production of animals fed urea treated rice straw are highlighted and discussed.
Key words: animal performance, nutritive value, rice straw, supplementation, urea
The major constraint to increasing livestock production in most tropical developing countries like Indonesia is the low availability of forage, both quantity and quality, especially during the dry season. During the season, due to limited availability of forages, many grasslands are undergoing overgrazing that causes many animals are forced to graze on marginal lands like forest margin, steep slopes, river bank etc. that sometimes lead to environmental problems. To alleviate the problems, many farmers feed their livestock with agricultural byproducts like rice straw, maize stover, banana wastes, etc. either as basal feed or supplement, although, their availabilities are mostly seasonal.
Rice straw is produced worldwide, mainly in the tropics. Globally, there are about 800 to 1000 million tons/year of rice straw are produced, which about 600 – 800 tons per year produced in Asia countries (Anonymous 2020). As the largest rice producer in Southeast Asian countries, Indonesia produces large amounts of rice straw. With assumption that rice grain: straw ratio was 1 : 1 (Matias et al 2019). it is estimated that in 2018 rice straw production in Indonesia attained 83.04 million tons (Badan Pusat Statistik 2020). This value is lower compared with rice straw produced in all Southeast Asian countries that attained about 200 million tons per year (Aquino et al 2019).
Although it is produced in large quantities, utilization of rice straw as animal feed is low. Only about 20% of rice straw are used for industrial (e.g. paper, ethanol) and domestic (e.g. fodder) purposes and. most of the remaining rice straws are left in the paddy field that serving as mulch, ploughed into the paddy soil or burned (Oladosu et al 2016). Much rice straw is burned because most farmers consider that field burning is the fastest and the cheapest way to remove large volume of rice straw biomasses although this practice pollutes the air and emits greenhouse gases like methane and nitrous oxide (Gaihre et al 2014).
The low utilization of rice straw as feed for ruminants is mainly attributed to the high NDF and ADF, lignification and silicification levels and the low levels of crude protein that lead to low intake, digestibility and palatability (Ravi et al 2019; Sarnklong et al 2010). Crude protein contents of unfertilized rice straw was 3 – 5% (Nori et al 2006) or 4.0 – 4.7% (Aquino, et al 2019) which lower than maintenance requirement of cattle (6.1 – 7.4%) as reported by Leibholdz and Kellaway (1982). NDF and ADF levels of rice straw are high (71.97 to 72.53%) and (39 83 to 43.52%), respectively (Sarnklong et al 2010), that make rice straw is classified as low quality feed (Anonymous 2020).
High NDF and ADF levels reduce dry matter intake and digestibility. The maximum dry matter intake of rice straw by ruminants is only about 1.0 to 1.2 % of live weight (Devendra, 1997; Drake et al 2002). In vitro dry matter and organic matter digestibility of rice straw were 33.6 – 53.3% and 35.3 – 56.3%, respectively (Peripolli et al 2016), These values are lower than the critical level of 65% required for feeds could be considered acceptable digestibility (Moore and Mott 1973).
High lignification and silicification of cell wall have negative impact on digestibility. The high contents of lignin (4.63 – 13.0%) and silica (4.25 – 13.0%) of rice straw (Sheikh et al. 2018) disrupts digestion of cellulose and hemicellulose (Thiago and Kellaway 1982). High silica and lignin reduce digestibility and degradability of rice straw by preventing colonization of rumen microbes (Agbagla-Dohnani 2003). Due to the low nutritional value, feeding untreated rice straw to animals does not provide enough nutrients even for maintenance needs of ruminants (Sheikh et al 2018) and animals fed untreated dry rice straw will lose their weight (Nguyen and Dang 2020). Therefore, to increase performance of animal fed rice straw, treatments to improve its nutritive value are needed.
Many studies have been conducted worldwide to improve chemical composition and nutritive value of rice straw. Physical, chemical and biological methods have been used to disrupt or break-down ligno-cellulosic linkage of cell wall. Ammoniation of rice straw by urea treatment may be suitable way for smallholder-farmers who keep animals in limited quantities because urea treatment can improve intake, crude protein and digestibility with low cost, relatively safe and easy to apply compared with ammoniation by liquid or anhydrous ammonia. Moreover, urea has higher effect on reducing NDF and ADF content and increasing in vitro dry matter and organic matter digestibility compared with liquid ammonia (Yalchi et al 2009). Furthermore, rate and extent of degradation of urea fermented rice straw are higher than urea supplemented rice straw (Mgheni et al 1993).
The objective of this paper was to review the relevant literatures concerning chemical composition and nutritional value of untreated and urea-fermented rice straw with urea and importance of supplementation with fermentable carbohydrate and protein bypass sources on urea treated rice straw and animal performance.
Urea fermented rice straw can enhance nutritive value of rice straw by increasing crude protein content and disrupting fiber structure.of cell wall. Increased crude protein level as influenced by urea treatment had been widely reported. The increased crude protein content from 2.5 to 5.4%, was reported by Gunun et al (2013), from 3.3 to 8.1% by Hossain et al 2010) and from 6.2 to 17.3 % by Pradhan et al 1996). Conversely, NDF and ADF contents of rice straw decreased by fermentation with urea. Sharma et al (2004) reported decreased NDF level from 88.4% to 84.1% and ADF level from 75.5% to 70% by urea treatment. Wanapat et al (2013) also reported a decreased ADF levels from 50 .3% to 47.7% and NDF levels from 63.7 to 54.1% as affected by ammoniation by urea treatment.
Nutrient digestibility of rice straw also increased by fermentation with urea. Dry matter and crude protein digestibility increased from 49 to 60% and from 50 to 60%, respectively by urea treatment (Wanapat et al 2013) Gunun et al. (2013) reported increased NDF digestibility from 55.9% to 65.2% and ADF digestibility from 53.45 to 60.1%. by fermentation with urea. Increased dry matter intake and digestibility of nutrients (dry matter, crude protein, organic matter, NDF and ADF) of rice straw treated with 2 + 2% urea-calcium hydroxide treated or 3% urea have also been reported by Wanapat et al (2013).
As effect of decreased NDF and NDF levels, feed intake and digestibility increased. Wanapat et al (2013) noted an increased intake of rice straw from 1.43 to 1.95% of body weight and dry matter digestibility from 49% to 60% as influenced by urea treatment. Dry matter rumen degradability of rice straw also improved by urea treatment. At 24 and 72 hrs of incubation, rumen dry matter degradability of untreated rice straw was 33.6 and 50.93% respectively while in urea-treated rice straw, at 24 and 72 hrs rumen incubation, dry matter degradability was 41.35% and 63.34% respectively (Ngele et al 2009) Due to improvement of nutrient contents, digestibility and degradability of urea treated rice straw, growth performance of animals fed urea-treated rice straw also higher. Cattle with 100-150 kg body weight lose 50-100 g/day when they were fed untreated straw, but they gained 50-100 g/day when fed urea-treated rice straw (Walli et al 1995). Wanapat et al (1996) also reported that compared with untreated rice straw, there were improvement of daily gain (200 g/d) of growing cattle and milk production (.0 to 2.5 kg/d) by animals fed urea-treated rice straw.
Although positive effects can be obtained by feeding urea-treated rice straw to animals, supplementation with deficient nutrients is needed to achieve full potential of animals. Unsupplemented urea-treated rice straw only lead to low levels animal production and this might be one reason for the low interest of the farmers to apply this technology.
The use of non-protein nitrogen (NPN) sources like urea has been reported to increase crude protein content and digestibility through better rumen fermentation. but for better results, urea-treated rice straw must be supplemented with fermentable energy that lacking in urea-treated rice straw. Readily available energy can improve rumen. Function and increasing microbial protein synthesis (Alam et al 2016). Fermentable carbohydrate source like molasses has been reported to supply energy that can improve cellulose and hemicellulose digestion. With increasing molasses levels in the diet from 5 to 25%, dry matter, rumen digestibility and organic matter rumen digestibility increased from 26.8 to 43.5% and 32.5 to 50.9%, respectively (Cakra et al (2018)
Besides increasing digestibility, supplementation urea-treated rice straw with molasses reduced NDF contents from 81.8 to 68.5%, ADF from 52.7 to 44.7% and increased DM intake from 580 to 759 g/d (Dulphy et al 1992). Increased daily gain of sheep fed urea- treated rice straw supplemented with molasses over urea-untreated and molasses-unsupplemented rice straw has been reported by Sheikh et al (2017). However. excessive use of readily fermentable carbohydrates may lower rumen function as affected by lowering rumen pH.
Like molasses, cassava tubers/roots have been used as source of readily fermentable energy in animal fed urea treated rice straw. Increased cassava tuber level from 0 to 15% linearly increased dry matter, organic matter and crude protein digestibility of urea treated rice straw (Noviandi et al 2017). Kang et al. (2012) reported that swamp buffaloes fed urea-calcium hydroxide treated rice straw supplemented with cassava at 1 and 2 g/kg BW and Leucaena leucocephala leaf meal at 300 g/d increased animals intake, dry matter digestibility and crude protein digestibility by 0.7 kg/d, 0.9% and 0.9%, respectively. Khampa et al (2009) reported that cattle fed urea-treated rice straw ad libitum supplemented with concentrate and yeast fermented cassava chip increased daily gain and digestibility compared with urea-treated rice straw supplemented with concentrate feed only. Cassava chip can be used up to 80% in concentrate and supplementation of concentrate at 2% body weight in cattle fed urea-treated rice straw as basal diets could improve efficiency of rumen fermentation (Wanapat and Khampa 2007).
Rice bran as energy source has positive effect when it is used as supplement by sheep fed urea treated rice straw. Increasing levels of rice bran increased total milk yield but butterfat content decreased (Hock et al 1988). Inclusion up to 20% rice bran significantly improved total dry matter intake, but at 20 to 30% level, ,organic matter digestibility also increased (Upreti and Orden, 2008).
Leaves of Sesbania sesban that has low cell wall constituents and high ruminal degradability (Kamatali et al 1992) could be considered as energy and fermentable N sources. Supplementation of Sesbania sesban leaves to sheep fed urea-treated rice straw as basal diet improved intake and digestibility of dry matter, organic matter and crude protein of diets. Daily gain and feed conversion efficiency were also higher in supplemented group than control. (Tekiye et al 2018).
The product of treating rice straw with urea in the rumen is ammonia which is easily fermented and degradable in the rumen, If animals are fed with urea-treated rice straw, most ammonia will be used by rumen microbes to make protein microbes and the rest N mostly wasted via urine. Generally rumen contains low levels of undegradable protein that may bypass in the rumen and digested in the small intestine. In highly productive animals, feeding urea-treated rice straw supplemented with rumen undegradable protein should be given greater attention because it is bypassed in the rumen for digestion and absorption in small intestine and provides additional protein for animals The use of rumen undegradable protein sources like vegetable protein rich in tannin such as Leucaena leucocephala, Gliricidia sepiu, cassava leaves, oil rich seed like cotton seed cake and animal protein are very beneficial used as supplement to improve utilization of nutrients by animals fed urea treated rice straw (Chenost and Kayouli 1997)
Sheep fed ammoniated rice straw and supplemented with Leucaena leucocephala or Gliricidia sepium leaves increased their total dry matter intake, nutrient digestibility, utilization and performance. Daily gain of animals fed amoniated rice straw only or supplemented with Leucaena or Gliricidia was 19.3, 34.6 and 33.9 g, respectively (Orden et al 2000).
Cassava leaves are good source of protein bypass. In Vietnam, cattle fed cassava leaves at 0 to 1% body weight and received basal diet of urea treated rice straw increased their dry matter and protein intake with increasing cassava level while daily gain increased from 201 to 402 g/d and feed conversion rate from 25.1 to 15.0 (Keo et al 2008). Also in Vietnam, when cattle fed mixture of rice straw, urea, molasses and minerals supplemented with cassava leaf meal at levels of 0, 0.25, 0.75 and 1% body weight, dry matter intake increased up to 1% body weight level but daily gain only increased up to 0.5% body weight level. This indicates that when animals fed cassava leaf meal at <0.5% body weight level, microbial protein requirement synthesis may be insufficient to satisfy metabolisable protein requirement (Tham et al 2008). The decreased body weight at 0.75 and 1% level might attributed to high levels of cassava leaf meal and tannin lthat led to more N wasted via feces.
High cattle production can be achieved with straw diet provided it is supplemented with good bypass protein source like soybean meal. Cattle received basal diet of urea treated rice straw and supplemented with soybean meal at 4% and 6% level increased their dry matter intake and total weight gain from 4.0 to 4.4 kg and from 20.2 to 25.6 kg, respectively (Ahmed et al 2002).
In China, Chinese yellow cattle fed basal diets of ammoniated wheat straw ad libitum and supplemented with cottonseed cake at 1, 2, 3 and 4 kg/day gained weight from 250, 600, 704, 845 and to 883 g/d with feed conversion rate of 20, 10, 9, 8 and 7, respectively (Weixian et al 1994). Singh et al. (2001) also reported that heifers fed urea treated rice straw supplemented with cotton seed cake to provide 15,30, 45 and 60% of their crude protein needs gained weight of 391, 325, 368, 471 and 494 g/day, respectively.
Rumen degradability of protein bypass sources are different. Soybean leaf meal and Leucaena leaf meal had higher rumen degradability and could be used to improve rumen ecology while cassava leaf meal and cottonseed meal are less degradable in the rumen and, therefore it is suitable to be used as bypass protein sources (Promkot et al 2007).
The author would like to thank Rector of Hasanuddin University, Dean Faculty of Animal Science Hasanuddin University, Ministry of Education Republic of Indonesia and my colleagues from Laboratory of Forage and Grassland Management for their support so that this article can be published successfully. I hope that with publication of this paper, much more wasted rice straw can be converted into valuable animal products.
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