Water spinach and mulberry leaves (Morus alba) as protein sources for growing pigs fed diets with different sources of energy
 

Chiv Phiny

Centre for Livestock and Agriculture Development, CelAgrid -Cambodia
phiny_kh@yahoo.com /chphiny@celagrid.org

1. Introduction

In Cambodia 85% of the population are farmers, earning their living through agricultural activities, including cultivation of crops and livestock production. Almost all farmers keep livestock, such as cattle, buffaloes, pigs and chickens. A survey conducted in a northeastern province of Cambodia showed that a family kept an average of 3.4 ± 0.149 head of cattle, 0.87 ± 0.106 pigs and 7.3 ± 0.719 adult chickens (CelAgrid, 2006a). Pigs are kept mainly for family income and so far few commercial pig farms are operated in Cambodia, mainly located close to the towns.Beside cash income livestock are an important source of protein for the rural families.

Monogastric animal production, especially pigs, has to be carefully considered, because they often compete with humans for food, and these feeds are generally the most expensive diet ingredients, particularly protein feeds. However, a potential solution is instead to use farm products and by-products that are locally available. Preston (2006) reported that the leaves from shrubs such as cassava and mulberry, sweet potato, and water plants such as duckweed (Lemna spp) and water spinach (Ipomoea aquatica), can be used successfully in diets for pigs to replace at least half the protein usually supplied as soya bean and fish meals. In animal production, the utilization of unconventional feeds for animal feeding will contribute to the reduction of food deficiency in the future.

Amongst potential tropical forages, mulberry leaves have not been given much attention as a protein source, particularly for feeding to pigs. Several studies on mulberry leaves for silk worm production have been carried out, which indicate that they could be a valuable source of protein for pigs (Chiv Phiny et al., 2003). Mulberry leaves have a crude protein (CP) content ranging from 18-25% in DM and have good biological value (Chiv Phiny et al., 2006). During the last decade a number of researchers have extensively studied the use of water spinach for pig feeding (Le Thin Men, 1999). However, few studies have looked at the interaction of mixed forages such as water spinach and mulberry in diets for pigs, and as both forages are accessible and easily cultivated by small scale pig producers in the rural areas, it is important to study them and document the results for wider distribution and dissemination.

When using forages in pig feeding it is also important to look at the energy sources and select those that are highly digestible and easily obtained in the rural areas. In this case, cassava root meal, rice bran, broken rice and sugar palm syrup are the potential sources of energy selected for study.

2. Hypotheses

Digestibility, N retention and efficiency of protein utilization would be higher, and growth rate and feed conversion would be improved: (i) when the energy component of the diet was low in fibre; and (ii) when the protein was derived from a mixture of mulberry leaves with water spinach rather than water spinach alone.
 

3. Objectives

The aim of the studies was to increase and improve the knowledge of the nutritional potential and utilization of water spinach and mulberry leaves as protein sources for growing pigs fed cassava root meal, rice bran, sugar palm syrup and broken rice. The specific objectives were to look at:

• The effect of water spinach or water spinach mixed with mulberry leaves on digestibility and N balance in pigs fed basal diets of cassava root meal plus rice bran or sugar palm syrup plus broken rice.

• The effect of water spinach or water spinach mixed with mulberry leaves on the performance traits of growing pigs fed basal diets of cassava root meal plus rice bran or sugar palm syrup plus broken rice.

4. General discussion

4.1. Limitations and advantages of non-conventional local feed resources for pigs

In Cambodia many different forage crops, water plants and agricultural products and by-products can be used for pig feeding. Duckweed, water spinach, mulberry and cassava leaves and sweet potato vines are rich in protein and can be grown by farmers, and these match with sources of energy available in the community, such as sugar cane juice, sugar palm juice and cassava root. The leaves of most water plants are more digestible than the leaves of trees and shrubs, but the high water content limits high levels of inclusion in pig diets, while forage crops often have low palatability and high fibre contents that negatively influence feed intake and therefore reduce the availability of nutrients to pigs (Cheeke et al., 1980; Rosales et al., 1993). For smallholder farmers a more appropriate approach is to grow trees, shrubs and water plants that produce much higher unit area yields of protein in the form of leaf biomass rather than cultivating traditional protein crops such as soybean, groundnut or sunflower as components of their farming systems (Udebibie, 1991; Pound et al., 1984). Strategies to efficiently utilize these unconventional feeds are more likely to succeed when the production system is matched with the available resources (Preston and Leng, 1987). However, the use of forages for pig feeding should consider the age of the plant, which is the most important factor influencing the composition and nutritive value of biomass products.

4.2 .Nutrient requirements of pigs

The nutritional requirements for pigs reared in tropical regions are different from those in temperate countries. The high ambient temperature reduces in the voluntary feed intake of the pigs (Preston, 1995), while in the temperate countries pigs need more energy from feed to keep them warm.

Two factors must be taken into account in deciding on the levels of protein that will be appropriate for pig diets in the tropics. The first is that, at least in SE Asia, the local "unimproved" pigs continue to play an important role, especially for the poorer farmers. Recent studies have shown that on the same diet, exotic pigs continue to respond with increases in growth rate up to 17% of protein in diet DM, but that local pigs (the Mong Cai) reach their maximum growth rate with only 15% of dietary protein (Ngo Huu Toan, 2003). In tropical countries, crossbred pigs play an important role, and are very interesting for farmers in rural areas because they are easy to look after, are fairly well adapted to the local feeds and environment, and their growth rate is higher than in local pigs. Studies on the protein requirement for maximum growth rate of crossbred pigs, such as that of Nguyen Thi Loc et al. (1996), found that Large White x Mong Cai had maximum growth rate (465g/day) with 12% of dietary protein. However, Bounlieng Khoutsavang, (2005) reported that maximum growth rate (552g/day) of crossbred (Large White x Mong Cai) pigs in Laos was when the dietary protein content was15%, similar to the value reported by Prak Kea et al. (2003) for cross breed pigs (Large White x Local) in Cambodia. However, Chhay Ty et al., (2006) reported that crossbred (Local x Landrace or Local x Duroc) growing pigs responded to a diet with 18% of CP in DM (367g/day), although a recent study by Thim Sokha et al. (2007 unpublished data) indicated that the maximum growth rate of crossbred pigs was on a diet with 14% CP when the protein was supplied by water spinach and sweet potato vine in basal diets of broken rice or cassava root meal plus rice bran. The second point is that most of the "tropical" energy feeds are low in protein, thus the minimum amino acid needs can be accomplished with lower overall protein levels than what are recommended for temperate countries (eg: NRC, 1988), which are inflated by the presence of excessive amounts of the non-essential amino acids present in cereal grains. Thus the protein supplied by Sarria et al. (1990) for growing pigs fed sugar cane juice and soya bean meal was only 200 g/day, less than 60% of the NRC (1988) standard, and yet the median growth rate in 8 on-farm trials was 590 g/day.

4.2.1. Protein and amino acid requirements of growing pigs

The quality of the protein in pig diets is often limited by a deficiency of one or two of the indispensable amino acids. The concept of limiting amino acids refers to the most deficient amino acid, and for pigs it is likely to be lysine. There are twenty amino acids required by animals, but some of these can not be synthesized by the animal or are synthesized at an insufficient rate to meet its requirement. For optimum performance the diet must contain adequate amounts of the essential amino acids, energy and other indispensable nutrients. Protein requirements may be stated in terms of the "ideal protein" (McDonald et al., 1995).

According to NRC (1988) and NIAH (1995), the pig has specific requirements for ten essential amino acids, and the ratio of amino acids to lysine is particularly important. For example the optimum ratio of methionine plus cystine to lysine is 50%, and threonine to lysine is 60% (Tables 1 and 2).

 

4.3. Water spinach (Ipomoea aquatica)

There are two varieties of water spinach, land and aquatic water spinach, grown on the land and in water, respectively. Water spinach can be grown in a range of soil types from sandy soils to heavy textured clay loams, but friable well-drained soils high in organic matter are preferred. The ideal pH range is 5.5 to 7.0 (NRE, 2000) but the best pH ranges for vegetable crops are from pH 6.0 to 7.0 in tropical areas. The optimum temperatures are between 24 to 30 ^oC, with at least 760 mm of rainfall a year (Rubatzky, 1991). Water spinach grows very well when fertilized with manure from livestock. The biomass yield of water spinach has been shown to respond dramatically to fertilization with biodigester effluent loaded with animal manure, with increasing concentrations of crude protein in the dry matter (Khean Sopphea and Preston, 2001; Ho Bunyeth, 2003; Ly Thi Luyen, 2003). Beside organic matter, water resources play an important role in the cultivation of both varieties. If water is allowed to stand in the field, the plant strikes roots at every node and becomes woody and inedible and then only the tender branches, twigs and leaves are used as greens. Therefore, correct maintenance of water is very important for getting a good biomass yield (Tiwari and Chandra, 1985).

Water spinach is cultivated as food for humans and forage for animals in Southeast Asia, especially for pigs (Göhl, 1981). The aquatic water spinach is propagated by cuttings and grows in the wild or is cultivated in fish ponds, lakes and open waste water, while the land water spinach is cultivated on dry or marshy land and it is propagated by seeds and cuttings (Palada and Crossman, 1999). The yield of land water spinach was up to 28 tons per ha per year, when harvested every 20-25 days with fertilization of 180 kg (effluent from biodigester) of nitrogen per ha per year, and it can be grown at any time of the year (Khean Sophea and Preston, 2001). The average annual yield in fresh basis of aquatic water spinach has been reported as 90, 70 and 100 tons/ha, in Hong Kong, Fiji and the Netherlands, respectively (Jain et al., 1987). The edible portion can contain up to 29% CP in DM basis. Water spinach likes other water plants such as duckweed and Azolla, is a highly productive source of protein-rich biomass and is an ideal complement for fibre-free basal diets such as molasses, sugar can juice and palm oil in poultry and pig diets (Preston, 1995).

4.3.1. Nutritive value of water spinach

There are two common varieties; the red and the white water spinach. Both varieties are used fresh for pigs and other animals. Nguyen Nhuy Xuan Dung (1996) reported that the crude protein in DM in the dry and rainy season was 23.6 and 27.6%, respectively, and crude fibre 15.5 and 14.0%, respectively, and these values are similar to those reported by Bruemmer and Roe (1979), Prak Kea et al. (2003) and Khean Sophea et al. (2001). Thacker (1990) reported that water spinach has a lower fibre content than alfalfa leaves (27.3%). Water spinach is also is also a good source of trace minerals (mg/kg): Zn, 5.03; Mn, 22.2; Cu, 1.37 and Fe, 75.3 (NIAH, 1995) and is rich in vitamin A and C (Vanzi, 1997). The chemical composition of the fresh whole water spinach plant is shown in Table 3.

4.3. 2. Use of water spinach as pig feed

In Cambodia and throughout Southeast Asia, water spinach is cultivated for human food and feed for pigs and other animals. Preston (2006) recommended that water spinach can provide 50% of the dry matter and 70% of the protein in diets for growing pigs. It was found to be highly digestible by pigs and supported higher N retention than similar diets in which cassava leaves were the supplementary protein source with basal diets of broken rice (8% CP in DM). Moreover, water spinach can not only be used alone as a protein source but it also has been used in a mixture with cassava leaves in the diets of crossbreed pigs. The results showed that the growth rate with water spinach alone was 356g/day, which was lower than the 383g/day on the mixture of water spinach and cassava leaves (Chhay Ty and Preston, 2005), and was higher than the growth rate in Paper II. Water spinach has also been used successfully to replace part of the protein in diets based on sugar cane juice for breeding sows in Vietnam (Le Thi Men and Bui Hong Van, 1993), and Sorn Suheang and Preston (2005) reported a growth rate of 320g/day when fresh water spinach replaced dried fish in diets for growing cross breed pigs fed whole sugar cane stalks or sugar cane juice. However, Prak Kea et al. (2003) reported that the growth rate (436g/day) was improved when dried fish was fed at a level of 6% in a diet of broken rice and water spinach. Ly et al. (2002) found significant improvements in growth rate (442g/day) when 0.5% of synthetic DL-methionine was added to a basal diet of broken rice and water spinach. This result is similar to Pech Sovanno et al. (2002), who reported an improvement in live weight gain (417g/day) when 0.5% of DL-methionine and water spinach were added a basal diet of full fat rubber seed and cassava root meal.

4.4. Mulberry (Morus alba)

There are about 68 species of the genus Morus, and the majority of them are found in Asia (Datta, 2000a). The most popular species in the world are M. alba and M. indica. Mulberry can grow very well in most soils and produce a high biomass yield with proper management. Proper planting density, fertilization and irrigation are important strategies to increase yield. In east China, it is recommended to plant 10,500-15,000 seedlings/ha to get 26,250kg/year of leaves. However, in South China, the average annual leaf production can reach 37,500-52,500kg/ha/year by increasing planting density to 90,000-120,000 per ha (Huo, 2000a). Mulberry flourishes well in soils that are flat, deep, fertile, well drained, loamy to clayey, and porous with good moisture holding capacity. The ideal range of soil pH is 6.2 to 6.8, the optimum being 6.5 to 6.8 and with annual rainfall ranging from 600 to 2500 mm. Sunshine is one of the important factors controlling growth and leaf quality. In the tropics, mulberry grows best with a sunshine range of 9 to 13 hours a day (Datta, 2000b).

Higher production of leaves can be achieved by sufficient fertilization. To get good yields, the proportion of N: P: K of 10: 4: 6 should be applied. The combination of fertilizer containing proper N P K levels and trace elements is widely used for cultivating mulberry (Huo, 2000b). However, biomass yield was increased when livestock waste in the form of compost or biodigester effluent was used (Rodriguez and Preston, 1996; Moog et al., 1997).

4.4.1. Nutritive value of mulberry leaves

Mulberry yields nearly 35-45tons of fresh leaf/ha/year, with 20-23 % CP, and 12-18 % minerals, in DM basis. The leaves contain about 70 % of moisture. The cell wall constituents are neutral detergent fiber 45.6 %, cell contents 54.4 %, acid detergent fiber 35.0%, hemicellulose 10-40 %, lignin 10 %, cellulose 21.8 % and silica 2.7 % (Lohan, 1980). The chemical composition of the leaves varies from season to season, and is shown in Table 4.

4.4.2. Mulberry leaves in pig diets

The most important use of mulberry (Morus alba) leaves is for silk worms. However, in Japan, India, Colombia and Cuba, researchers have used mulberry leaves for animal feeding (FAO, 1999). Furthermore, the nutritional value of mulberry leaves means that they are an ideal supplement in most diets and are equivalent to grain-based concentrates. The leaves contain 20-23 percent CP in DM basis and are acceptable as a forage for feeding to farm livestock (Lohan, 1980). In Cambodia, CelAgrid has also been developing ways to use mulberry leaves for livestock, particularly for feeding to pigs. For example, Chiv Phiny et al. (2003) reported that crossbred pigs showed a slight preference for fresh versus sun-dried leaves; however, a more interesting finding was that the DM digestibility increased linearly (R²=0.86) with increasing proportions of mulberry leaves in the diet (range of 0 to 50% mulberry leaves in the diet DM). From these data (Y = 0.131X + 75.9, where Y is % DM digestibility and X = proportion (%) of mulberry leaves in the diet DM), it can be predicted that with 100% mulberry leaves in the diet, the digestibility would be 89%, and the N balance tended to be better in pigs fed fresh mulberry leaves compared to mulberry leaf meal rice-based diets. However, González et al. (2006) reported a study where mulberry (Morus alba) leaf meal (MLM) was used in diets of growing crossbred pigs with a basal diet of corn meal or sugar cane juice-high protein mix. The results showed that daily weight gain was higher when 8 or 16% of MLM was mixed with the basal diets of corn meal (CM) or sugar cane juice-high protein mix (CJP). Thus 8 or 16% MLM and the use of CJP permitted substituting 89.0 and 91.6% of conventional ingredients, and gave live weight gains (LWG) of 741g/d and 568g/d, respectively. Chhay Ty et al. (2007 unpublished data) found that the digestibility values of dry matter were higher in fresh mulberry leaves as compared with a mixture of mulberry and sweet potato vine, and N balance was higher when a basal diet of broken rice was used. These results are similar to our experiment for DM digestibility when water spinach alone compare with the mixture of water spinach and mulberry leaves. However, in Paper I of this thesis N balance was higher for the mixture of foliages than water spinach alone. The use of mulberry leaves with other forages, such as the combination of mulberry leaf and water spinach, or mulberry leaf alone fed with an energy component such as cassava root meal and rice bran, or sugar palm syrup and broken rice has not been much studied.

4.5. Cassava (Manihot esculenta Crantz) root

Cassava is a tropical crop and one of the twelve most important food crops grown in the world. The adverse climatic conditions in most parts of Africa favour production of cassava, which can tolerate drought, poor soils, many pests and diseases and does not compete with other food crops for inputs and time during planting and harvesting (Boccas, 1987). The largest producer of cassava is Brazil, followed by Thailand, Nigeria, Zaire and Indonesia. Production in Africa and Asia continues to increase, while that in Latin America has remained relatively level over the past 30 years. Thailand is the main exporter of cassava, with most of it going to Europe. It is a staple food in many parts of western and central Africa, and is found throughout the humid tropics (Stephen, 1998). In Cambodia, farmers cultivate cassava for mainly tuber production and a large increase in production was observed in 2002-2003 due to the introduction of a new variety and a high market demand. Generally the harvesting period of cassava is 6-8 months after planting, and without fertilization the tuber yield ranges from 4-6 tons/ha (Khieu Borin and Frankow-Lindberg, 2005). However, the national average tuber yield in 2003 was 13.2 tons/ha, although with yields of up to 18.3 tons/ha (FAO/RAP, 2003). The major potential products of cassava are the root and leaves, after processing through sun-drying, ensiling, chipping and wilting, as a livestock feed, particularly as protein and energy sources in diets for pigs and ruminants (Müller et al., 1975). In Cambodia, small-scale farmers have practiced two methods of cassava root processing: firstly sun-drying, and secondly ensiling after the roots have been cleaned and chopped into small pieces. Moreover, cassava roots are processed in factories, producing flour that can be used for baking and making bread. Cassava root can also be used in livestock diets after sun-drying or ensiling.

4.5.1. Nutritive value of cassava root

Whole fresh cassava roots contain the cyanogenic glucosides, linamarin and lotaustralin. They are converted to HCN in the presence of linamarase, a naturally occurring enzyme in cassava. Linamarase acts on the glucosides when the cells are ruptured. In the roots, the peel has a higher concentration than the interior. Sweet cultivars can contain as little as 20 mg of HCN per kg of fresh roots, while bitter ones may produce more than 50 times as much. Under-processed roots of high HCN cultivars may result in serious health problems (Onwueme, 1978; Kay, 1973). Fresh roots contain approximately 65 percent water and have to be dried or processed to extend their shelf life or to preserve them. Cassava root contains 1-2% CP, 0.2-0.5% ether extract, 0.8-1.0% crude fibre, and 1-2% ash in dry matter (Gomez, 1979). The nutritive value of cassava root meal is presented in Table 5.

4.5.2. Cassava root meal for pigs

Cassava roots are a good energy source but are low in protein, making the economic utilization of roots in animal feeds highly dependent on the incorporation of other protein-rich ingredients (Balagopalan et al., 1988). In a digestibility study on the use of cassava root meal Bui Huy Nhu Phuc and Lindberg (2000) reported that the digestibility of EAA and non-essential AA (NEAA) was higher in groundnut foliage (0.71 vs. 0.56, and 0.73 vs. 0.57, respectively) than in other foliages, with or without inclusion (150g/kg) of sun-dried cassava leaves, ensiled cassava leaves, leucaena leaves and groundnut foliage. Gomez and Valdivieso (1983) found that nursery pigs (from weaning to 20-25 kg live weight) could use 20-30% cassava root meal in the diet and performed similarly or slightly better than pigs fed a control diet based on corn-soybean meal. Liliana Ospina et al. (1995) reported that feeding pigs throughout the growing-finishing period with cassava root meal ad libitum, combined with 200 g/day of CP, gave acceptable growth performance and carcass quality, and the lowest feed costs/kg gain. Du Thanh Hang and Nguyen Thi Loc (2005) reported that the live weight gain of growing pigs was 404g/day and profitability was satisfactory when using diets consisting of molasses (43%), cassava root meal (37%), groundnut cake (10%) and green vegetables (10%) as total dry matter of the diet. In addition Nguyen Thi Loc et al. (1996) found that mean live weight gains of crossbred pigs were 465g/day for a cassava root meal diet and 453g/day for an ensiled cassava root diet replaced by 20% of 'A' molasses. Growth rate was not significantly different, but was slightly lower and feed conversion rate poorer, compared with the cassava root meal diet.

4.6. Rice bran

Rice is the major food grain of the world and it is the principle cereal consumed in India and other parts of Asia. Milling of paddy to obtain edible rice grain yields two major by-products of economic and nutritional importance, namely, paddy husk and rice bran. Paddy husk has no food value but has several industrial uses. Rice bran, on the other hand, can serve as an animal feed, as a human food supplement and as a valuable source of edible oil (Narasinga Rao, 2000). In Cambodia, rice bran is a good local energy source for livestock in the rural areas. There are two different qualities of rice bran, and the quality of both products depends on the milling machine. The price of rice bran varies, based on these qualities. Farmers use rice bran directly for chickens and ducks, but they boil it with vegetable wastes or kitchen residues before feeding to pigs.

4.6.1. Nutritive value of rice bran

The nutritive value of rice bran in Cambodia varies according to rice variety, but much more depending on the milling process. Rice bran contains on average around 12.9% CP and 8.6% CF. Harris and Staples, (2003) also reported that rice bran contains about 12% CP, 12% fat, 10% CF and 60% TDN (as fed). High fat rice bran frequently becomes rancid when stored for long periods. Rice bran is high in phosphorus and low in calcium. Narasinga Rao, (2000) found that rice bran has a higher lysine content and a lower glutamic acid content than rice and wheat, and it has a better balance of essential amino acids, with an amino acid score of 80 per cent with respect to lysine, and 90 per cent with respect to threonine. Rice bran with 15 to 20 per cent oil can serve as a good source of energy and essential fatty acids (EFA). The minerals in rice bran, such as calcium, iron and zinc, may not be so available due to its high phytate content. Rice bran is also a rich source of B-complex vitamins, particularly thiamine and nicotinic acid, and some other minor B-vitamins. The chemical composition of rice bran is shown in Table 6.

4.6.2. Rice bran as a source of energy for pigs

In Cambodia rice bran is the most common ingredient used for livestock feeding, particularly in small-scale farms. Farmers cook rice grain with vegetables collected nearby, with water plants from lakes and ponds or with kitchen residues or vegetable wastes and then boil the mixture before feeding it to pigs. In some provinces, farmers have been trained by some organizations to improve pig feeding and management using local feed resources such as rice bran in combination green leaves. CelAgrid has introduced the use of cassava leaves and water spinach as a supplement to traditional diets of rice bran, and 180 families in 6 villages in Takeo province at present are using this technology. Khieu Borin et al. (2000) reported that that during 5 months on a diet of ad libitum sugar palm juice, 500 g/day of rice bran and 400 g/day of freshwater fish silage crossbreed pigs had growth rates of 325-476 g/day (average of 405±47 g/day). Chittavong Malavanh and Preston (2006) indicated that increased urinary N loss and decreased N retention when increasing the proportion level of water spinach replaced by sweet potato leaves, fed basal diets of cassava root meal plus rice bran. This result is similar to our experiment, where there was an increase in urinary N and lower N retention when the protein source was water spinach alone compared with the combination of water spinach and mulberry leaves (Paper I). However, Chanphone and Choke (2003) found that when Stylo 184 was used as a replacement for rice bran in diets for Laosian indigenous pigs DM intake was 82.7g (6.4% of diet DM) when feeding a diet consisting of 50% maize + 20% rice bran + 30% Stylo 184. The average daily live weight gain was 320 g/day, and DM conversion ratio was 4.00 kg feed/kg gain.

4.7. Broken rice

Broken rice is separated after the polishing stage. There is seldom any surplus of broken rice available for feeding to livestock, as it is normally mixed back with the whole grain rice and sold as low grade rice. The whole rice contains 20% hulls, 10% bran, 3% polishing, 1-17% broken rice and 50-60% polished rice (Göhl, 1975). It is low in fibre and is a good energy source for pigs, particularly when mixed with protein-rich green foliage.

4.7.1. Nutritive value of broken rice

The chemical composition of a good sample of broken rice is similar to that of polished rice but feed quality material may contain some contaminations. Broken rice has a high digestible energy (DE) content of 14.5 MJ/kg, which compares with 15.5 MJ/kg DM for polished rice. Broken rice is relatively low in protein but the essential amino acid balance is good (Farrell and Warren, 1982). The chemical composition of broken rice is shown in Table 7 and 8.

 

4.7.2. Broken rice as a source of energy for pigs

Broken rice is palatable and rich in energy. It has been used for all classes of livestock, but it is of special value in rations for growing chickens and pigs because of its high energy value and low fiber content (Göhl, 1975). In Cambodia, some farmers use it by mixing with green vegetables (for example aquatic water spinach, amaranthus, water hyacinth, taro leaves etc), which they harvest from their farm or from surrounding households. The mixture is usually fed after boiling and gives a reasonably good growth performance. Chhay Ty and Preston (2005) reported that there appeared to be synergistic positive effects on growth performance, with average live weight gain of 383g/pig per day from combining two sources of protein-rich leaves (water spinach and fresh cassava leaves) as supplements to a low protein basal diet of broken rice. However, in our experiment the growth rate was lower than this result when supplementing the mixture of water spinach and mulberry leaves, and with a basal diet of sugar palm syrup plus broken rice (Paper II). Bounhong et al. (2004) found that there were no differences among treatments in digestibility of dry matter and N when cassava leaves were fed alone or mixed with stylo as compared with stylo as the only supplement. They concluded that fresh cassava leaves can safely be fed to growing pigs and will support better performance than stylosanthes foliage when the basal diet is broken rice.

4.8. Sugar palm syrup

The palm tree (Borassus flabellifer) is considered to be a very important multipurpose tree and it is also the national symbol of Cambodia. The whole tree is used for many purposes, for example the juice for sugar production, leaves for thatch, trunk for timber and fruit for animal and human consumption. According to Khieu Borin et al. (1996) the sugar palm juice can be processed into three types of sugar at the small farm level: liquid sugar (sugar palm syrup), solid palm sugar and block sugar. Sugar palm syrup production is one of the two main activities of most rural Cambodian farmers after rice growing. The activity commences in December with the preparation of materials for sugar syrup production. Furthermore, Khieu Borin et al. (1996a) reported that sugar palm trees are a component of an integrated farming system and are generally found in paddy fields and around the Chamka (farm), with other crops such as cassava, sweet potato, mung bean, maize, etc. In a 5 months season, the sugar palm tree produces around 750kg of juice, equivalent to a production of 100kg of sugar. In Cambodia, sugar palm syrup production is still important for human and livestock consumption and is a source of seasonal income for farmers. However, at the present time in the rural areas, although some farmers are producing sugar palm syrup to meet market demand, others have stopped producing it because of a lack of fire wood, which is expensive to purchase, and is necessary for boiling the juice into sugar. As a result, the price of syrup is too high for it to be used for feeding to livestock. However, Khieu Borin et al. (1996b) found that the unprocessed palm juice can be fed directly to pigs, and is more profitable than feeding the syrup.

4.8.1. Nutritive value of sugar palm syrup

The palm tree produces seasonally an average of 5 kg of juice per day with a Brix value (approximate sugar content) of 13.3%, and this can be increased to approximately 80% by evaporation (sugar syrup) (Khieu Borin et al., 1996). According to Paulas and Muthukrishnan (1983) sugar palm juice has high nutritive value due to its high soluble carbohydrate content (98.4% of dry matter). The chemical composition of sugar palm syrup is shown in Table 9.

4.8.2. Sugar palm syrup for pigs

Although skilled labour is demanded for the production of sugar palm juice, it is still the cheapest rural energy source for pig feeding in Cambodia. Most farmers in the rural areas can get access or produce it during the late rainy season and throughout the dry season, and it fits well with the time when farmers begin to fatten their pigs in each season of the year. Mena (1988) reported that sugar cane juice is a good source of cheap energy in diets supplemented with high fibre vegetable protein and water plants. Preston and Murgueitio (1992) reported that leaves and water plants are good complementary sources of tropical biomass, providing protein to balance the carbohydrate in sugar cane and fruit crop by-products. Preston (1995) reported that the growth rate of pigs was about 500g per day when palm juice was fed as the basal diet with supplementation of 300g daily of boiled grain soybean and green vegetables. Moog et al. (1994) carried out on-farm trials in the Philippines where pigs were fed either fresh sugar cane juice and sugar syrup or muscovado sugar with a supplement of 500g of soya bean meal per pig per day, and noted an average live weight gain of 420 to 450g/day. Khieu Borin et al. (1993), quoted by Khieu Borin et al. (1996a), reported that when a small number of pigs was fed sugar palm juice ad libitum supplemented with 156g CP per pig/day, the pigs had a better performance than those on traditional diets. The average live weight gain in that study was almost 500g/day. The results from this author showed a higher growth rate than the growth rate (255g/day) in the present experiment when feeding water spinach mixed with mulberry leaves, and with basal diets of sugar palm syrup plus broken rice (Paper II). Preston (1995) and Leng et al. (1995) also mentioned that when low protein basal diets such as sugar cane and sugar palm products and by-products are fed to monogastric animals, the total protein needed is reduced considerably. This is because the ratio of essential amino acids is close to the optimum when the animal is supplemented with tree foliage and water plants such as Nacedero (Trichantera gigantea), duckweed (Lemna ssp), water spinach (Ipomoea aquatica) and azolla (Azolla anabaena). Feeding sugar palm syrup or juice, together with tree foliage and water plants as a source of protein, is a cheap and sustainable system for small-scale farmers in the rural areas of Cambodia.

Those reviews above have shown that the vegetative protein sources from water spinach, mulberry leaves, cassava leaves and so on can be used successfully in diets for pigs to replace at least half the protein usually supplied as soybean and fish meals. The potential of the forage is to be very useful is facilitated when they are accompanied by energy sources that are low in both fibre and protein. The vegetative source of the protein has a low digestible energy density because of the relatively high cell wall content. Thus, the forage could be a factor limiting intakes by pigs. One way to correct this problem is to combine the leaves with energy sources that are low in fibre. Cassava root meal, sugar palm syrup, palm oil, sugar cane juice, rice bran and broken rice are energy sources with low or zero content of fibre and protein. When energy sources are low in protein they can be combined with leaves which normally have well balanced arrays of amino acids. Chittavong Malavanh and Preston (2006) reported increasing urinary N and lower N retention in growing pigs, as a result of increasing the proportion of water spinach replacing the fresh leaves of sweet potato. The report is similar to our experiment (Paper I) that provided support for the first hypothesis that levels of water spinach above 35% of the total diet lead to increased losses of N in urine and poorer N retention. However, Chhay Ty and Preston, (2005) showed that the growth rate was higher and feed conversion rate better when the level of water spinach was reduced from 48% to 19.5% in the diets, without addition of DL-Methionine. In this study water spinach and cassava leaves were used as protein sources with a basal diet was broken rice, which was similar to our experiment (Paper II). Also Chhay Ty and Preston (2006) noted a higher intake and growth rate on a diet where increasing the replacement of cassava leaves by less than 30% of diet DM by water spinach when the basal diet was cassava root meal mixed with rice bran or broken rice, gave results that were similar to our results (Paper II). Feed conversion ratio was also better when water spinach was used at a low level in the diet.

4.9. Digestion and utilization of fibre by pigs

Animals can use nutrients in food when the food is broken down into simpler compounds that pass through the mucous membrane of the alimentary canal into blood and lymph. Mulberry, sweet potato and water spinach leaves are available in the rural areas through cultivation or growing wild, but contain high levels of fibre and water which limit the capacity for their utilization. However, the utilization of structural carbohydrates or fibre in growing pigs largely depends on the level of fibre fed, source of fibre, stage of forage maturity, and level of other nutrients in the diet (Farrell and Johnson, 1973; Close, 1993). The utilization of fibre is very important in monogastric species, especially pigs, because the digestion of fibre may highly influence performance traits of economic importance (Siers, 1975; Frank et al., 1983). The addition of fibre might also be involved in inducing satiety through increasing gut distension and high fibre levels in diets for pigs increase the time needed to consume the daily allowance according to Mroz et al. (1986), quoted by Andersson and Lindberg (1997).

From 94-99% of all carbohydrates are digested by the time they reach the terminal ileum in pigs. However, the digestion of hemicellulose and cellulose up to ileum is very limited and the amount of carbohydrates and other nutrients transferred from small intestine into large intestine is highly dependent on diet composition (Fernandez and Jorgensen, 1986; Dierick et al., 1989; Bach Knudsen and Jorgensen, 2001; Keys and DeBarthe, 1974). Digestibility of lignin by large intestinal microbes is very limited, and the lignin is not degraded in noticeable amounts (Fernandez and Jorgensen, 1986; Dierick et al., 1989). Most fibre digestion occurs in the caecum and large intestine of pigs and is a microbial fermentation process. The volatile fatty acids resulting from fibre fermentation serve as an energy source for growing pigs and can provide from 5 to 28% of the energy requirements (Friend et al., 1963; Farrell and Johnson, 1973).

5. Conclusions

• Cambodia is a country that is dependent on agriculture, with about 75% of the labour force employed in this sector. The 13 million people in Cambodia require more food, including meat, and therefore to meet this demand an important strategy is to reduce the use of grain in animal feeds by looking more to other alternative locally available resources for livestock, especially agricultural byproducts such as rice bran, broken rice, cassava root meal, sugar palm syrup, mulberry leaves and water spinach.

• Water spinach is a potentially valuable supplement for monogastric animals. It is used by farmers as a vegetable for human consumption and for feeding to pigs. It can produce high biomass yields and is rich in protein when adequate amounts of plant nutrients are available.

• Mulberry leaves are also locally available and are high in protein and also a potentially valuable protein supplement for pigs when mixed with a low protein energy source.

• Using by-products such as rice bran, cassava root meal, broken rice and sugar palm syrup as energy sources, together with foliages or water plants as protein sources in pig diets results in a sustainable system based on locally available natural resources with a high potential for small-scale farmers.

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