Urea Treated Rice Straw as a Basal Diet for Growing Ruminants: Supplementation with Protein Rich Forages
 

Khuc Thi Hue

Goat and Rabbit Research Center Sontay, Hatay

National Institution of Animal Husbandry, Hanoi, Vietnam

Hienhue02@yahoo.com

Sheep production, population, distribution and management in Vietnam

The Phan Rang sheep belong to the short-thin tail type and are considered to have an ability to survive in harsh conditions (Mai et al., 2003). After years of natural selection and adaptation, the mature weight of the Phan Rang sheep has stabilized at 39 kg to 45 kg for rams and 34 kg to 38 kg for ewes. The age at puberty is 5.5 to 6 months. The ewes produce on average 1.55 lambs per year and the length of gestation is 148 to 151 days. The lambing interval is 208 to 262 days and daily live weight gain of lambs in the period from 0 to 12 months of age is 68 g to 73 g/day (Binh et al. 2003). According to the data of National Statistics Department of Vietnam 3.3% of the sheep population can be found in the North and 96.7% in the South of Vietnam. The annual growth rate of the number of sheep in 1990 to 2000 was 17.8% per year, 116.5% between 2000 and 2004, and as high as 268.0% only between 2004 and 2005 (Vietnam National Statistic Department, 2000, 2004 and Report of Bureau of Animal Husbandry, 2006). The sheep breeds and their distribution have also changed rapidly from 2004 until today (Table 1, 2).

According to Binh and Lin (2005), there are three systems of management of small ruminants in Vietnam (intensive, semi-intensive and extensive systems), whereas, the two main systems for management of sheep in Phan Rang are the extensive system and the semi-extensive system (Mai et al., 2003). The semi- extensive system can normally be found on large private or state farms, with herd sizes ranging from hundreds to thousands. In this system, the sheep are allowed to graze during the day time and are supplemented with feeds during the night time. In the extensive system, most sheep are privately owned and are mainly kept by rural smallholders, and the flock size is usually between 10 and 100 head. The sheep are grazed all day and brought back to the house at night time, and are not given any supplementary feed. Some exotic sheep breeds, such as Dorper and White Suffolk, were imported by the government from Australia recently for use in intensive systems in Vietnam. In these systems, the sheep are kept in individual pens (Devendra and McLeroy, 1982) and feeds (or nutrients) are supplied entirely from the outside.

Urea treated rice straw

 Rice straw production in Vietnam      

Rice straw is the most abundant feed resource for ruminants in Vietnam, and plays an important role, especially in the dry season, when roughage is normally in short supply (Chinh and Ly, 1996). According to Trach (1998) the annual rice production increased from 11.8 million tonnes in 1976 to 16 million tonnes in 1986, and reached 26.3 million tonnes in 1996.

This increased rice production is a very important factor behind the increasing total number of ruminants. It is estimated that each kg of rice harvested is equal to one kg of rice straw produced (Chowdhury et al., 1995; Devendra, 1997) but according to Trach (1998) only to 0.83 kg of rice straw. Based on this estimation, there are 25 to 30 million tonnes of rice straw produced every year in Vietnam, and there are many different rice straw varieties. It is considered though, that rice straw is not yet maximally utilised as a feed for ruminants. A large amount of rice straw is burnt in the field or used for other purposes such as cooking, mushroom production or litter. Moreover, when used as a feed for animals, it is normally in the untreated form, without any supplementation, even though methods for improving the utilisation of rice straw have been developed and recommended. According to Trach (1998) this is because of the fact that few local research and extension activities have been undertaken, leading to a poor understanding about ruminant nutrition and feeding and little information and training about the most appropriate techniques have been given to the farmers.     

Urea treated rice straw as a feed for ruminants

The major limiting factors when feeding rice straw are that the quality and microbial digestion in the rumen are low, as is the CP concentration (Preston and Leng, 1987) and the low content of vitamins and minerals (Trach, 1998). Also the high silica content in the wall of the epidermal cell layer and the vascular bundles (Chandra, 1994; Van Soest, 1994) results in low voluntary intake (Preston and Leng 1987). The amount of silica in the rice straw depends on the variety, fertilizer application, irrigation and harvesting time (Winslow, 1992; Deren et al., 1994). These factors are the main cause of the difference in rice straw degradation (Singh, 1994; Vadiveloo and Phang, 1996).

Urea treatment is an accepted technique for enhancing the nutritional quality of rice straw in terms of increasing the nitrogen content (Shen et al., 1998a; Khang and Dan, 2001) and improving the digestibility (Chowdhury and Huque, 1996; Man and Wiktorsson, 2001; Trach et al., 2001a,b). Urea treatment promotes saponification of phenolic ester linkages (Dias-da Silva and Guedes, 1990) and reduces the hemi-cellulose content (Dias-da Silva and Sundstol, 1986; Shen, 1993; Shen et al., 1998a). When evaluating the quality of urea treated rice straw from three cultivation seasons through in vitro and in sacco degradation measurements, Shen et al. (1998b) found that in rice straw treated with 5% of urea the degradation of cellulose and hemi-cellulose increased, and the dry matter (DM) and organic matter (OM) in sacco losses after 48 h of incubation increased by 24.0% and 30.7%, respectively, and the extraction of silica also increased. In addition, in a study on the effect of ammonia treatment on physical strength of straw, distribution of straw particles and particle-associated bacteria in sheep rumen, Selim et al. (2004) found that the strength was significantly lower for ammonia treated straw fragments, compared to untreated straw fragments in both the in situ and in vivo studies. Furthermore, the mass of bacteria tightly associated with straw particles was significantly higher in the ammonia treated straw diet at 2 h after feeding. Ammonia treatment of the straw also reduced the DM proportion of the large particles (5600 µm), and medium particles (1180 to 5600 µm) and increased the proportion of small particles (300-1180 µm).

Several feeding trials using urea treated rice straw for ruminants have been conducted. Chinh et al. (1992) reported that the feed intake and growth rate of crossbred growing Shindhi x Local Vietnamese cattle fed a diet of 2.5% urea treated rice straw + 0.5% lime and 0.5% salt were improved compared to feeding untreated rice straw supplemented with molasses urea block, but there was a cost advantage with feeding untreated rice straw and molasses urea block supplementation. Trach et al. (2001a) found that treatment of rice straw with 2% urea and 3% calcium hydroxide increased the OM intake (OMI) by 32% and 24% in growing calves and bulls, respectively. Feed utilization, growth rate and digestibility in beef cattle was increased when they were fed a diet of 4% urea and 3% limestone treated rice straw (Trach et al., 2001b). Feeding urea treated rice straw to sheep was studied by Hue et al. (2003). The results indicated that 2.5% urea treated rice straw could be used for sheep, but when 20% molasses was added to 2.5% urea treated rice straw DM intake (DMI) and live weight gain (LWG) were increased. A diet with rice straw sprayed with 20 g urea in one litre of water and Gliricidia forage supplementation (Pathirana and Orskov, 1995) or 4% urea treated straw with 0.5% limestone and 0.5% salt supplemented with protein forages such as Stylosanthes, Cassava and Jackfruit (Paper I) increased the DMI, LWG and DM digestibility in growing sheep. It seems that 4% of urea can be recommended as a suitable level for treating rice straw for sheep. When using this formula the CP concentration in the rice straw can be improved by over 209% compared to untreated rice straw (113g/kg DM in (Paper I) versus 54 g/kg DM (Khang and Dan, 2001)), 244% (Khang and Dan, 2001) and the DMI of UTR (4% of urea) is about 15 to 20 g/kg of BW and 30 to 50 g of CP from the UTR can be the expected intake in lambs (Paper I).

Potential of protein rich forages as feed for ruminants

Stylosanthes forage 

Stylosanthes guianesis (other Latin names include Stylosanthes erecta Beauv., Stylosanthes gracilis Kunth, Stylosanthes guineensis Schumacher or Trifolium guianense Aublet) is one of the species among the 45 species of the Stylosanthes genus of the subtribe Stylosanthinae and Leguminous family (Tarawali et al., 2005). It is considered to be indigenous to Brazil and naturally distributed in the tropical, subtropical and temperate regions of the Americas, Africa and Southeast Asia (‘t Mannetje, 1984), especially in Australia, Brazil, Colombia, Peru, China and Thailand (Peters, 1992). It is a perennial herb or sub-shrub, multi-branched and usually erect, reaching a height of 1.5 m. Its leaves are trifoliate with leaflets 0.5 to 4 cm long and 0.2 to 1.5 cm wide. The flowers are 1 to 4 cm long and yellow in colour. The stems are hairy and become woody at the base with age. The seeds are about 2.2 mm long and 1.5 mm wide, mostly pale brown, but varying from yellow to black (Smith and Albert, 1985). Stylosanthes guianensis grows on a wide range of soils, including lighter, poorer quality soils with pH from 4.0 to 8.3. It is suited to warm humid areas with high rainfall (Smith, 2002) and is not considered to be shade and salt tolerant. It also does not tolerate being cut close (lower than 10 cm) to the ground, since there are few buds on the lower stem for re-growth (Phengsavanh and Ledin, 2003) and subsequent cuts must be made higher than 25 cm to ensure good re-growth (Horne and Stür, 1999).

Stylosanthes guianensis has been used to intercrop with cereal plants such as maize to improve the quality of the soil, and intercropping did not adversely affect the grain yield (Undi et al., 2001). Intercropping Stylosanthes with millet did not significantly affect grain yields during the establishment year, but total biomass and CP yields were increased by 45% and 125%, respectively, when millet was planted into pre-established Stylosanthes during the second year, although the millet grain yield decreased by more than 30% (Kouame et al., 1996). Stylosanthes is also used as a short-term fallow crop for improving upland rice productivity (Saito et al., 2006). According to Tarawali and Ikwuegbu (1993) the soil chemical and physical properties under Stylosanthes fallow were improved (1.14 g N, 4.31 g organic carbon and 34*10⁷ microorganisms/g) compared to natural fallow (0.87 g N, 2.70 g organic carbon and 36.4*10⁷ microorganisms/g).

Stylosanthes forage is currently used for grazing cattle, buffaloes, sheep, goats and pigs or as a cut and carry feed in the form of fresh, hay or leaf meal. The CP concentration of Stylosanthes guianensis was 154 g/kg DM (Paper I) with 50 to 60 days of harvesting frequency. The DM digestibility of young plant material is around 600 g to 700 g/kg, but it may decrease to 400 g/kg DM with increasing age and lignification (Matizha et al., 1997).

Njwe and Kona (1996), in a comparative evaluation of Stylosanthes guianensis hay and concentrate as protein supplements to a basal diet of elephant grass for West African sheep, found that the DM digestibility was similar (693 g and 724 g/kg DM) for the diets supplemented with Stylosanthes guianensis hay and concentrate, and significantly higher than for the diet with only elephant grass (566 g/kg DM). The result in Paper I also indicate that Stylosanthes forage when offered to growing sheep, can be a protein source that can replace the concentrate. Supplementing Stylosanthes forage at up 30% to 40% of the total diet for goats increased the LWG (63.9 and 70.5 g/day) compared to a diet of Gamba grass only (Phengsavanh and Ledin, 2003). Stylosanthes was used as pasture for grazing cattle and goats in Nigeria (Mani et al., 1988), and Bunaji cattle given access to Stylosanthes pastures for 2 to 3 hours per day in the dry season produced more milk, lost less weight, had shorter calving intervals and had better calf survival rate. In a similar study on West African Dwarf goats by Tarawali and Ikuegbu (1993) in the wet season, non-pregnant adult goats grazing on Stylosanthes pastures had reduced weight loss compared to goats grazed on natural pastures.

Cassava foliage

Cassava (Manihot esculenta Crantz) is a perennial woody shrub of the family Euphorbiaceae. It originated in South America and is extensively cultivated as an annual crop in the tropic and sub-tropic regions for the dual purposes of tuberous roots as source of energy for humans and animals and foliage as a feed for animals. The plant may grow to a height of 3 to 4 meters (Silvester, 1989) or of 6 to 8 feet (Stephens, 2003). It has smooth erect stems and deep, well distributed roots (Dung et al., 2003). The dark green, reddish veined leaves are divided into seven leaflets, the stems contain soft white pith and have nodes from which new plants are obtained (Stephens, 2003). Cassava thrives in sandy loam soils with low organic matter (Van et al., 2001), and in areas receiving low rainfall and with high temperatures (Wanapat et al., 1997).

According to Mui et al. (1994) the leaf biomass is about 5 tonnes/ha when the root is harvested after 9 to 10 months. Khang (2004) indicated that the harvesting height and cutting interval affected the biomass yield of Cassava foliage, and 10 cm harvesting height and 45 day cutting intervals resulted in the highest foliage yield (25 tonnes in fresh form or 5.31 tonnes of DM per harvesting, which equals 1.0 to 1.5 tonnes of CP).

Cassava foliage is recognized as a locally available feed resource for both non- ruminants and ruminants (Preston, 2001; Wanapat, 2001) with 19.7 tonnes of DM/ha (Dung et al., 2003) and as a valuable source of protein, producing 2.24 tonnes and 2.84 tonnes/ha according to Preston (2001) and Dung et al. (2003), respectively, and minerals and vitamins.

The CP concentration of cassava foliage was highest (190 g to 210 g/kg DM) with 60 to 90 days cutting interval and 10 cm harvesting height, and the same CP concentration in the Cassava foliage was found in Paper I, 202 g/kg DM at 90 to 120 days of harvesting time.      An early study by Moore (1976) showed that the feed intake, growth rate and feed efficiency of steers were improved when supplemented with 25% of Cassava foliage to a basal diet of Napier grass. In another study by Ffoulkes (1978) the feed DM consumed by cattle fed chopped cassava foliage was only up to 2% of body weight (BW) with a fairly high DM digestibility of 665 g/kg. Supplementing crossbred Sindhi x Yellow cattle with Cassava foliage resulted in increased DMI, CP intake and LWG with an increased level of CP supplementation by Cassava foliage of 0 to 100 g/day (Khuong and Khang, 2005).

Cassava foliage is also used as a protein supplement for small ruminants. Research by Sokerya and Rodriguez (2001) indicated that the highest growth rate was when the goats were supplemented with Cassava leaves as compared to diets with 3 different foliages based on brewer’s grain. Do et al. (2002) also found that increasing the DM intake of Cassava leaves by goats over the range of 0 to 47% of the total DM of the diet resulted in increased DMI, OM digestibility and N retention. The result in Paper I also showed that Cassava foliage can be used as a replacement for concentrate in diets for growing lambs and give the same LWG (77 g vs 73 g/day). The LWG of lambs obtained in Paper I was similar to results recorded by Binh et al. (2003) for Phan Rang sheep raised in northern Vietnam (68 g to 73 g/day). 

Jackfruit foliage

Jackfruit (Artocarpus heterophyllus Lam) is indigenous to the rain forests of the Western Ghats of India and spread early to other parts of India, southeast Asia, central and eastern Africa, Brazil and Surinam (Morton, 1987). The tree is handsome and stately, and 9 to 21 m tall. The leaves are evergreen, 22.5 cm long, oval in the mature tree, and sometimes oblong or deeply lobed on young shoots (Morton, 1987). Jackfruit has adapted only to humid tropical and near-tropical climates. It is sensitive to frost in its early life and can not tolerate drought. In many regions of Vietnam, Jackfruit trees are planted for fruits in the home gardens of the farms, with 4-15 trees distributed per farm.

The fruit tree has no commercial importance, but as a fodder tree it can produce considerable amounts of edible biomass (Makkar, 1993; Mui et al., 2001). According to Tien et al. (1996) the optimum cultivating density of Jackfruit is 250 trees per hectare and the edible biomass yield ranges from 37 to 63 tonnes/ha. Jackfruit leaves have a high protein content of approximately 170 g/kg DM (Viet, 1997; Nhan and Preston, 1997) with 80 g digestible CP g/kg (Das and Ghosh, 2001) and is a good source of Ca and Na (Ibrahim et al. 1998) and a valuable feed resource for ruminants.

Jackfruit foliage can replace up to 100% of a concentrate based on protein content for goats (Mui et al. 2001) and for growing sheep (Paper I). The optimal replacement level of Jackfruit foliage based on CP content for a home-made concentrate of rice bran-soya bean is 50% for growing goats (Mui et al., 2001) and 40% for dairy goats (Mui et al. 2002), which gave a similar LWG, milk yield and milk quality as the control diet. Das and Ghosh, (2007) reported that replacing 50% of commercial concentrate by Jackfruit foliage resulted in reduced daily gain of Black Bengal goats and the recommendation was 25% of Jackfruit foliage in the diet of growing goats. 

The LWG was not affected by 100% replacement of concentrate by jackfruit foliage for growing sheep (Paper I). However, the digestibility of DM and CP of the diet including Jackfruit foliage was lower compared to the diet including concentrate, so the sheep needed a higher DMI to get the same amount of nutrients as the control. For the diets with replacement of concentrate with Stylosanthes forage or Cassava foliage, the sheep consumed less DM comparing to the diet with Jackfruit foliage, but this resulted in similar LWG because of a higher CP digestibility.

Effect of tannins on internal parasites

Tannins play a significant role in the nutrition of animals, causing either adverse or beneficial effects on nutrient utilization, health and production (Mui et al., 2005). The major beneficial effect of tannins is the protection of plant protein from digestion in the rumen and making the protein available for digestion and utilisation in the lower gut (Waghorn et al., 1990; Norton, 1999). However, tannins above 50 g/kg DM can become an anti-nutritional factor in plant material (Wang et al., 1996) and result in reduced voluntary feed intake and digestibility (Salunkhe et al. 1990; Barry and McNabb, 1999).

There are two chemically distinct types of tannins: hydrolysable tannins (gallotannins and ellagitannins) and condensed tannins (flavolans). According to Mui et al. (2005), forages containing condensed tannins have the potential to help to control anthelmintic-resistant gastrointestinal parasites by direct or indirect biological effects. The direct effect might be mediated through interaction between condensed tannins and nematodes affecting physiological function of gastrointestinal parasites (Nieze et al. 1998; Athanasiadou et al., 2000; Molan et al., 2002). The direct effect of condensed tannins is through interference with parasite hatching and development of infective stage larvae (Molan et al., 2002). According to Barry et al. (2001) and Nieze et al. (2002), the indirect effect of condensed tannins may enhance resistance of gastrointestinal parasite infection through increases in protein supply, which are prioritised for tissue repair and immune response. Condensed tannins and nutrients binding directly inhibit nutrient availability for larval growth or decrease gastrointestinal parasites through inhibition of oxidative phosphorylation (Scalbert, 1991).

The viability of the larval stages of several nematodes in goats and sheep was decreased by condensed tannins extracted from forages (Kahn and Diaz-Hernandez, 2000). Molan et al. (2000) found that the rate of larval development and number of eggs hatched was reduced 91% and 34%, respectively, through the effect of condensed tannins extracted from L. pedunculatus, L. corniculatus, H. coronarium and O. viciifolia forages.

Economical evaluation on practical production

Protein rich forages such as Stylosanthes, Cassava or Jackfruit can be used in practical production, since this is an alternative way of solving the problem of high costs and low availability of concentrate, and the most important limitation of the Vietnamese farmers is lack of cash for investments. Moreover, Jackfruit is a traditional tree for Vietnamese farmers and is cultivated in their homesteads with annually 10 to 15 trees/household and can produce from 150 kg to 250 kg of biomass/tree/year by pruning without affecting the fruit yield (Tien et al., 1996). Cassava is also a common food crop for Vietnamese farmers, especially in the hilly and mountainous areas where the land is not possible to use for growing rice. Stylosanthes is a new potential feed for animals in Vietnam and the response to growing Stylosanthes has been positive by the farmers, because of its ease of in cultivation, rapid harvesting time and high biomass yield. The use of shrub legumes can provide some of the protein at a considerably lower cost. A study by Mui et al. (2001) indicated that Jackfruit foliage used as a supplement at level of 40% can give a higher net income with a price of only 5000 VND/kg of milk. In a study with growing goats using Cassava hay as a protein source to replace concentrate, Dung et al. (2003) found that 25% replacement (or 9% in total DMI) of the diet for growing goat resulted in the highest net income. In Paper I, the profit of sheep production was improved when using protein rich forages such as Stylosanthes, Cassava and Jackfruit to replace concentrate, and the reduction of the feed cost was 90.5%, 56.2% and 35.7% of the control. According to ILRI (1998) a new technology can be recommended if net income increases and variables costs remain the same or decrease. 

Conclusions

Based on the results above, it can be concluded that:

• Stylosanthes forage, Cassava foliage and Jackfruit foliage are potentially valuable feeds for ruminants and can be used to replace up to 100% of the concentrate in the diet for growing lambs fed a basal diet of urea treated rice straw and molasses, with a similar LWG and lower feed costs.
• Feeding foliages containing tannins such as Cassava and Jackfruit can decrease the numbers of parasite eggs in the faeces.   

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