Effect of different protein levels derived from mixtures of water spinach and fresh sweet potato vines in basal diets of broken rice or cassava root meal and rice bran for growing pigs

Thim Sokha

Royal University of Agriculture,

Faculty of Animal Science and Veterinary Medicine, Cambodia

Sokha_rua@yahho.com

Table of contents

1. Introduction. PAGEREF _Toc169680197 \h 1

2. Hypothesis. PAGEREF _Toc169680198 \h 3

3. Objectives. PAGEREF _Toc169680199 \h 3

4. General discussion. PAGEREF _Toc169680200 \h 3

     4.1. Pig production systems. PAGEREF _Toc169680201 \h 3

        4.1.1. Local feed resource for Pig production in Cambodia. PAGEREF _Toc169680202 \h 4

         4.2. Water spinach (Ipomoea aquatica ) PAGEREF _Toc169680203 \h 5

        4.2.1. Chemical composition of water spinach. PAGEREF _Toc169680204 \h 5

        4.2.2. Water spinach foliage as a feed source for pigs. PAGEREF _Toc169680205 \h 6

         4.3 Sweet potato (Ipomoea batatas L (Lam.)) PAGEREF _Toc169680206 \h 7

        4.3.1. Chemical composition and nutritive values of sweet potato vines. PAGEREF _Toc169680207 \h 7

        4.3.2. Sweet potato vines as feed for growing pigs. PAGEREF _Toc169680208 \h 8

         4.4. Utilization of fiber in pig diets. PAGEREF _Toc169680209 \h 8

     4.5. Protein and amino acid requirements of crossbred growing pigs. PAGEREF _Toc169680210 \h 9

     4.6. Energy sources for pigs. PAGEREF _Toc169680211 \h 10

5. Conclusions. PAGEREF _Toc169680212 \h 11

7. References. PAGEREF _Toc169680213 \h 11

Introduction

            Pig production in Cambodia is currently characterized by small-scale free range systems, with some medium and large scale production units. However, small scale pig production so far dominates the supply of pig meat in Cambodia. To a certain extent, human food residues, rice products and water spinach (Ipomoea aquatica) and other foliages are major components of the daily ration (Khieu Borin 1994; Cameron and Twyford-Jones, 1995). In general, small scale animal production is dependent on locally available feed resources such as rice bran, sugar cane tops, sweet potato vines, cassava roots, and agro-industrial by-products from marine food processing and brewing. Commercial feeds are rarely used because these are expensive. The proportion of commercial feed used is about 20 % of the total, while the remaining 80 % is mainly crop residues and farm by- products, which are often of poor quality and low nutritional value (An et al., 2003). The question is how to improve the nutritional quality of diets in small-scale pig production systems and thus improve the production capacity of the animals. It is also important to look for simple and appropriate technologies which farmers can easily adopt and which will lead to better income.

Fattening pigs is one of the sources of farm cash income for the rural farmers in Cambodia. Devendra (1993) reported that there was an average annual growth rate of 16.6% of the pig population in Cambodia and that was the highest rate among the countries of South-East Asia. Generally, piglets are purchased after the rice harvest. The reason for buying piglets at this time is that farmers will have enough money and feed available from rice by-products (Khieu Borin, 1996). Rice bran is one of the main by-products used in pig raising. Rozemuller (1998) reported that the rice bran produced by traditional mills in Cambodia is of low energy density, which limits its potential as an energy source to complement fibrous sources of protein such as water spinach. Broken rice is another by-product of rice milling but with the advantage of a high energy density as it is almost free of fiber. Preston and Sansoucy (1987) and Preston and Leng (1987) have suggested that one way to achieve sustainable animal production systems is to match them with the available local resources. Nevertheless there are also other important factors that affect the pig production systems, such as management, breeds and mortality caused by infectious disease and parasites.

            The large water surface areas in Cambodia have brought advantages to farmers for crop cultivation particularly water spinach which can be grown almost year round for use as human food and feed for animals Water spinach (Ipomoea aquatica) grows equally well in water or in soil and it responds dramatically in biomass yield (24 tonnes/ha/cut) and protein content more than 20% in DM when it is fertilized particularly with biodigester effluent (Kean Sophea and Preston, 2001). Le Thi Men et al. (1999) reported that the annual yields of water spinach can be as high as 455 tonnes fresh biomass (about 40 tonnes DM) per ha. The short production cycles (25-30 day per cut) make water spinach a potential crop in the Mekong region. The fresh leaves and stems of water spinach have high crude protein content in the range of 18 to 31% in DM (Le Thi Men et al., 2000; Bui Huy Nhu Phuc, 2000; Prak Kea et al., 2003). The plant is also rich in minerals with an ash content of 12% in dry matter (Göhl, 1981). It has been used successfully to replace part of the protein in sugar cane juice based diets for breeding sows (Le Thi Men and Bui Hong Van, 1993) and as the main protein source for growing pigs fed broken rice (Ly, 2001; Prak Kea et al., 2003). The high yield potential enables farmers to get a regular high income from harvesting water spinach for their pigs and selling it to local markets.

            Although water spinach has high protein content, its digestibility is rather low. Ly et al. (2002) reported that the in vitro digestibility of the crude protein was only 56% compared with 75% for duckweed. The low energy density in water spinach is a limitation but could be corrected by supplementing energy-rich feeds such as cassava root meal. The protein in water spinach is deficient in sulphur amino acids according to Le Thi Men, (1999) and Bui Huy Nhu Phuc (2000), while sweet potato vines are deficient in lysine (Le Van An, 2004), thus there could be advantages in combining these two forages as the protein supplement in basal diets of broken rice and rice bran, available locally in Cambodia.

            Sweet potato (Ipomoea batatas (L) Lam) is a tropical crop with a relatively short vegetative cycle, the tubers of which are used for both human and animal consumption (Woolfe, 1992). It is among the five most important food crops in developing countries (Horton, 1988) and is the third most important crop after rice and maize, in many areas of Cambodia such as Kandal, Kampong Cham and Takeo Provinces. Sweet potato is planted near the Mekong river after rice harvesting and it is often used as animal feed. The tubers have a high carbohydrate content while the leaves are rich in protein, and both tubers and vines can be used as animal feed (Woolfe, 1992). The vines include the leaf and stem, with a crude protein content in the leaves of 260-330 g/kg DM compared with 100-140 g/kg DM in the stems (Ishida et al., 2000; Le Van An et al., 2003). It has been shown that the leaves make up approximately half of the sweet potato vines biomass (Woolfe, 1992; Le Van An et al., 2003). Thus, if the leaves can be separated from the stems a considerable improvement with respect to the dietary protein and amino acid supply would be expected (Le Van An et al., 2003). Sweet potato based pig production systems are very common in Cambodia and play an important role in the economies of small scale farmers (Peter, 1998). The productive potential of certain varieties of sweet potato can reach 24-36 tonnes/ha/crop of roots (Morales, 1980) while the foliage production varies from 4.3 to 6.0 tonnes DM per ha (Ruiz et al., 1980).

The primary reason for using forages is to save grain crops for human consumption. Pig production systems serve as family savings for short-term needs, such as school fees, books or clothing for children. Moreover pig meat provides part of the dietary protein for the rural family (Chantalakhana et al., 2002) Many alternative feed resources are available in Cambodia but more research is needed as to how best they can be used in pig feeding. It is also important that the alternative feed resources can be grown on the farm as this will directly benefit the poorer farmers, who do not have cash resources to purchase supplements from outside the farm.

Hypothesis

Diets for pigs based on broken rice or cassava root meal, supplemented with water spinach and sweet potato vines, will have an amino acid balance close to that in the “ideal” protein. The optimum level of protein in the diet will therefore be less than recommended for diets based on maize and soybean meal (NRC 1998).

When the protein is from forages, growth performance will be better when the energy source is low in fibre (broken rice) compared to an energy source higher in fibre (cassava root meal plus rice bran).

Objectives

        To study effects on growth rate and feed conversion of pigs of:

·        Different levels of crude protein derived from combinations of sweet potato vines  and water spinach

·        Energy sources derived from broken rice, cassava root meal and rice bran

General discussion

Pig production systems

            Khieu Borin et al. (1996) reported that fattening pigs is one of the popular practices to generate income of farmers in the rural areas in Cambodia. Generally, piglets are purchased after the rice harvest. The reason for buying piglets at this time is that farmers have enough money and feed available from rice by-products, which is the major feed ingredient. Piglets in the rural areas are sold with average live weight of 4 to 6 kg at the age of about 40 to 50 days. A high mortality rate is observed at this stage because they are offered the same quality of diet as given to older pigs. Cunha (1977) recommended that piglets should be supplemented with a diet containing 22% CP of a good quality.

            The definition of a small-holder pig farm varies amongst countries. For instance, in Philippines and Vietnam a small farm has less than 20 pigs, while small farms in Cambodia and Laos have less than 5 pigs (FAO, 2003). Small-holder farmers are mainly located in rural areas. The economic failure of small-scale pig production is often due to high mortality of young piglets. Farmers commonly buy piglets from middlemen at the time of the rice harvest. Such piglets are generally not adapted to the small-holder environment and often cannot survive on the poor quality diets and mortality is also caused by stress during the transportation. Productivity of the village pigs is generally low, with litter sizes of three to five piglets and low growth rates (less than 120 g per day). Past efforts to increase productivity by the introduction of improved pig breeds into the traditional village system have not been successful (e.g. Walters, 1981), largely due to poor management, parasites and diseases.

Pig production systems in Cambodia are becoming more important, especially in smallholder farms, where they account for about 80% of the total pig population (Kinh et al., 2002). Feeding is the main factor which influences pig performances. The smallholder farm systems are based on the use of farm-produced feedstuffs and agricultural byproducts and traditional feeding management. The feeds utilised are characterised by high fibre content and low amounts of protein and energy (Loc et al., 1997). Monetary input in feeding in these systems is low. In these pig production systems, crop byproducts may occupy from 84% to 97.5% of the total feed (Lan, 2000; Kinh et al., 2002). The use of those feed resources also depends on the seasonality of production.

Lan (2000) reported that farmers keep either sows or fattening pigs, or both sows and fatteners Generally speaking, 1 to 2 sows and 3-5 fattening pigs are kept per smallholder (Singh et al., 1996); or 1-5 pigs (Lan, 2000); or 1-2 sows and 2-10 fattening pigs are kept in smallholder farms depending on the families’ situation (Ogle and Phuc, 1997). Socio-economic conditions of smallholder farms greatly affect pig keeping. Pig production is better developed in rich smallholder farms but is not well performed in poor smallholder farms with low number of piglets per litter and low number of litters per sow per year (Thuan et al., 2000). In addition, Valle Zárate et al. (2003) mentioned that rich households can keep big herds of fattening pigs while a poor household can keep only one sow or a few fattening pigs because of lack of available household resources. In smallholder farms in the study region, pigs may be sold after weaning for fattening/breeding purpose, and as fatteners for slaughter. However, farmers may sell fattening pigs earlier than the optimum weight due to cash or feed shortages (Lemke et al., 2002). Almost all pig producers in Vietnam sell pigs as live animals (Kinh et al., 2002). Most of the smallholder farmers sell pigs through middlemen. The price of pigs is based on the estimated carcass quality in case of fattening pigs (Kinh et al., 2002). In smallholder farms, pig keeping is mainly a task of women and children, which is especially true for pig feeding (Tung, 1999).

Local feed resource for Pig production in Cambodia

            Pigs in the rural areas in Cambodia are commonly raised by allowing them to roam around for their feed especially in the dry season. Pigs are fed with kitchen waste, sometime supplemented with banana stems, water spinach, sweet potato vine, duckweed and rice bran. The composition of the diet will depend on the money available to buy feeds and availability of by-products from the farmers’ own paddy rice mill. Generally, pigs grow slowly due to the shortage of feed and its poor quality. The main limitation in the diet in this region is the lack of protein supplements. Solarte et al. (1994) reported that the growth rate of pigs under the traditional management system in Colombia was only 60g/day, but when supplemented with 200g of crude protein daily, the weight gain increased in a range of 243-445 g/pig/day. The performance of pigs in the rainy season is usually better, as the free range pigs are able to find supplementary feeds, like earthworms, snails and green leaves which improves their protein intake. On the other hand, poorer performance may result in the rainy season because the pigs are tethered during the period of rice cultivation. Another potential source of protein for pigs in Cambodia is fish which can be harvested at the beginning of the dry season (December) and made into silage. However, few farmers have access to this resource, due to the lack of cash and accessibility. Therefore,  high-protein forages that can be grown on the farm would appear to have most potential for improving small-holder pig production, as these feeds can also be a part of their farming systems.

            There are many potential local feed resources such as forages and water plants like sweet potato vines (Ipomoea batata), water spinach (Ipomoea aquatica), water hyacinth (Eichhornia cressipe), groundnut foliage (Arachis hypogaea L.), cassava leaves (Manihot esculenta), duckweed (Lemna spp) and Leucaena  (Leucaena leucocephala) which can be used by small scale pig producers in Cambodia (Table 1). Water plants grow wild in the ponds and canals close to farmer households during the rainy season. In Cambodia duckweed is mainly used as duck feed. Elliott et al. (1987) and Preston et al. (1992) suggested that water plants represent a highly productive source of protein-rich biomass which appears to be an ideal complement for fibre-free basal diets such as molasses and sugar cane juice in pig diets. When effectively managed duckweed yields 10-30 tonnes DM per ha per year, and contains up to 43% CP, 5% fat and highly digestible dry matter which can be used as a protein  source for pigs with only slightly less efficiency than soybean meal (Leng et al.,1995).

Water spinach (Ipomoea aquatica )

            Water spinach (Ipomoea aquatica) is a plant that grows equally well in water or in the soil. There are two common types of water spinach; land and aquatic water spinach. The two types bear different flowers and leaves. Land-grown water spinach has long, narrow leaves with pointed ends and bears white flowers. The succulent foliage and stem tips are light green in colour. To obtain seeds, harvesting of the plants is stopped to allow developing flowers to mature, from which seed bearing pods form. Two main cultivar groups can be distinguished: var. aquatica and var. reptans. The aquatic water spinach grows in marshy or wet sandy areas, or floating on the water. It produces a number of adventitious roots, and along the edges of low lands the roots exert a binding effect on soil. It has 3 main cultivars: Red Green, Light Green and Red Stem, in which Red Green is the most common type in the tropics (Tiwari and Chandra, 1985). Water spinach is a member of the family Convolvulaceae, and it is commonly used as a green vegetable in India, South-east Asia, Malaysia, Taiwan and China (Jain et al., 1987; Bruemmer and Roe, 1979). Besides being a biomass resource and source of food, it can also be used in waste water treatment.

4Chemical composition of water spinach

            The edible portion can contain up to 29% crude protein comparable to alfalfa leaves (Thacker, 1990). Moreover, water spinach has a lower fiber content than alfalfa leaves (Bruemmer and Roe, 1979). The fresh leaves and stems of water spinach have crude fiber and ash concentrations around 12% and 19% of DM, respectively (GÖhl, 1981). Tran Hoang Chat et al. (2005) reported that water spinach foliage had a high potential as a supplement to concentrates for rabbits and supported higher live weight gain, milk yield and lower feed cost, compared with guinea grass.  Water spinach is also a rich sources of minerals and vitamins, being especially rich in vitamin A (carotene), B1, B2 and C and in iron (Oomen and Grubben, 1978; Naren Tong et al., 1994). The trace mineral contents of fresh water spinach (mg/kg DM) were: Zn 5.03, Mn 22.2, Cu 1.37 and Fe 75.3 (NIAH, 1995) (Table 2).

            The chemical composition of cultivated water spinach (DM basis), in the dry and rainy seasons, respectively, was: crude protein 23.6 and 27.6% and crude fibre 15.5 and 14.0% (Dung, 2001).

Water spinach foliage as a feed source for pigs

            Water spinach (Ipomoea aquatica) is cultivated for human food and used as feed for pigs and other animals in Cambodia and throughout Southeast Asia. The fresh leaves and stems of water spinach have a crude protein content of between 25.6 and 31% in DM according to Chhay Ty et al. (2007) and Bui Huy Nhu Phuc, (2000). The feeding of water spinach for growing pigs has been studied in Vietnam (Le Thi Men, 1999; Bui Huy Nhu Phuc, 2000) and Cambodia (Prak Kea et al., 2003). It has been used successfully to replace part of the protein in a diet of sugar cane juice for breeding sows in Vietnam (Le Thi Men and Bui Hong Van, 1993).

            Prak Kea et al. (2003) reported a linear increase in growth rates in pigs fed water spinach, palm oil and broken rice when up to 6% fish meal (in diet DM) replaced equivalent amounts of water spinach, which they attributed  to an improved amino acid balance, especially in terms of the sulphur-rich amino acids.  According to Ly (2002), it does not appear to contain anti-nutritional compounds. There are conflicting reports as to it is use as the sole source of supplementary protein in diets for growing pigs. Ly et al. (2002) observed significant improvements in growth rate when synthetic DL-methionine was added to a basal diet of broken rice and water spinach. Chhay Ty and Preston, (2006) reported no improvement from supplying synthetic methionine to a basal diet of broken rice and water spinach.

            Naren Tong et al. (1994) reported that a vitamin/mineral premix did not need to be included in diets containing water spinach as no deficiency symptoms of ducks were observed when water spinach was a major component of the diet. The ability of water spinach to supply minerals and vitamins is an important advantage in the rural areas where premixes are not usually available or are expensive. Vitamins are required by animals in very small amounts compared with other nutrients. Nevertheless a continuous deficiency in the diet will result in a disordered metabolism and eventually disease (McDonald et al., 1992).

Sweet potato (Ipomoea batatas L (Lam.))

            The sweet potato, Ipomoea batatas L. (Lam.), is a tropical crop with a relatively short vegetative cycle and is a major source of food for humans and feed for animals. In Cambodia, sweet potato is grown alongside the Mekong River because the sandy soils allow it to grow well. The growing cycle is completed within 100 to 150 days. The productive potential of certain varieties of sweet potato can reach from 24 to 36 tonnes/ha/ crop of roots (Morales, 1980) and the foliage production can vary from 4.3 to 6.0 tonnes DM/ha/crop (Dominguez, 1992; Ruiz et al., 1980). The aerial part of sweet potato is mostly composed of vines and has been utilized as animal feed in traditional backyard animal production systems. About 80% of the sweet potato in the world is grown in Asia, below 15 % in Africa and about 6% in the rest of the world (Horton, 1988). Sweet potato can be cultivated under many different climatic conditions but preferably on lightly acid or neutral soils, with the optimum pH being between 5.5 and 6.5. Soils which are excessively acid or alkaline often encourage bacterial infections and negatively influence roots yields (Cairo, 1980). For the cultivation of sweet potatoes a range of temperature between 15 to 33°C is required during the vegetative cycle, with the optimum temperature being between 20 to 25°C. The highest yields are obtained when temperatures are high during the day (25 to 30°C).

Chemical composition and nutritive values of sweet potato vines

            The protein content and quality of sweet potato vines are the most important factors that deserve attention when sweet potato is used as a feed. Several environmental factors have been shown to influence protein content in sweet potatoes. The effects of genotype on crude protein content are well described (Purcell et al., 1972, Edmond and Ammerman, 1971) as are those of cultural management and growth duration (Purcell et al., 1976). Dominguez and Ly (1997) reported that the vines low in soluble carbohydrate content but higher in fibre and protein and so their principal nutritive value is as a source of vitamins and protein. An et al. (2003) founded that the proportion of total essential amino acids (EAA) in ensiled sweet potato leaves was 0.95 of that in fresh leaves. Further, the contents of arginine (0.95), histidine (0.82), lysine (0.87), methionine (0.82), cystine (0.69), tyrosine (0.91) and glycine (0.66) were lower in the ensiled than in the fresh material.

            The leaves have superior contents of DM and CP compared with stems (Le Van An, 2003). Crude protein content in DM of sweet potato vines ranges from 16% to 29% (Dung, 2001), and the fibre content of the leaves is lower than that in water spinach, leucaena leaves, groundnut foliage and cassava leaves (Phuc, 2000). The vines have a protein content of 18.5% (Dominguez, 1992), while the leaves have CP content of 25.6-32.4% in DM (Woolfe, 1992; Ishida, 2000). Sweet potato can also be a source of other nutritionally important dietary factors, such as vitamin A, ascorbic acid, thiamin, riboflavin and niacin (Table 3).  Walter et al. (1984) reported lysine and/or tryptophan are limiting amino acids. 

Sweet potato vines as feed for growing pigs

            Sweet potato roots and vines are common feed for pigs, and other livestock, in many countries in Asia, including China, India, a few eastern islands of Indonesia, Korea, Philippines and Vietnam. In China, for example, which produces 85% of the world production of sweet potato, a large part of the crop goes to feed animals, mainly pigs (Scott, 1991) and in Papua New Guinea it has been estimated that 40% of sweet potato production is fed to pigs (Sowei, 1991). In Cambodia, feeding sweet potato root to pigs is common used in the rural area and it is cooked before feeding. Before feeding to pigs, the vines are usually chopped into small pieces. Silage offers a potential alternative to preserve sweet potato vines during the harvest of the roots and whenever there is a seasonal lack of feed for pigs (Brown and Chavalimu, 1985). Moreover, there is also the economic advantage of ensiling as a means to store the sweet potato vines during the harvest season when vines are cheap. Ensiling may also increase nutritional value and feed efficiency if it involves a fermentation process that converts non-protein nitrogen into protein (Gerpacio et al., 1967).  Sweet potato vines are almost exclusively used as animal feeds. Usually, vines are used directly as feed without precooking. Some adverse effects have been reported in monogastrics animals such as swine, and these were attributed to high fiber content and low digestible energy (Yeh and Bouwkamp, 1985). Domínguez and Ly (1997) included sweet potato vines in diets for growing pigs and reported that due to the high fibre content, the vines had a low CP digestibility.

            Le Van An (2004) reported that sweet potato leaves are higher in protein content compared to many other protein-rich forages and that lysine was the first limiting amino acid. Growing pigs fed sweet potato leaves with addition of synthetic lysine had daily live-weight gains of 536 g day, which was similar to that of pigs fed a control diet with fish meal as the protein source (542 g day). However, without addition of lysine to the sweet potato leaf diet daily live-weight gain was only 482 g day. According to Ruiz et al. (1980), the fresh vines can provide up to 27% of the dry matter and 40% of the total dietary protein for growing/finishing pigs.

Utilization of fiber in pig diets

            The role of fiber in monogastrics animal species such as the pig is very important, due to the fact that digestion of fiber may influence performance traits of economic importance (Siers, 1975; Frank et al., 1983). In this respect fiber utilization in growing pigs largely depends on the level of fiber fed, source of fiber, stage of forage maturity, and levels of other nutrients in the diet (Farrell and Jørgensen, 1973; Close, 1993). Feeding diets with high fiber content will increase the time needed to consume the daily allowances (Morz et al., 1986). A high level of fiber might also be involved in inducing satiety through increasing gut distension. According to Fernandez and Jørgensen (1986), Dierick et al, (1989) and Bach Knudsen and Jørgensen (2001), 94-99% of all carbohydrates are digested by the time they reach the terminal ileum in pigs. However, digestion of hemicelluloses and cellulose up to the terminal ileum is very limited (Keys and DeBarthe, 1974), and the amount of carbohydrates and other nutrients transferred from the small intestine into the large intestine is highly dependent on diet composition. Digestibility of lignin by the large intestinal microbes is very limited, and lignin is not degraded in noticeable amounts (Fernandez and Jørgensen, 1986; Dierick et al., 1989).

            According to Bach Knudsen (1997) and Souffrant (2001), dietary fibre is defined as a heterogeneous mixture of structural and non-structural polysaccharides and lignin and is not digested by endogenous secretions by the pig, but may be digested efficiently by the microbial flora. Dietary fibre is generally considered as a fraction with low energy content and in the pig causes regular peristaltic action that avoids the possibility of constipation (Wenk, 2001). In growing pigs, digestibility coefficients of dietary fibre average 0.4-0.5 but they range from around zero in high lignin and water-insoluble dietary fibre sources (e.g. wheat straw) to 0.8-0.9 in fibre sources with high pectin or water-soluble dietary fibre levels (e.g. sugar beet pulp or soybean hulls) (Noblet and Le Goff, 2001). The digestibility of dietary fibre is lower in young animals than in adult animals and the negative effects of dietary fibre on the digestibility of energy and nutrients are highest in young animals (Bach Knudsen and Jørgensen, 2001).

Protein and amino acid requirements of crossbred growing pigs

The pig’s requirements for total protein are usually determined in feeding trials in which growth rate is the main criterion of adequacy, and are stated as the concentration of protein in the diet. Pig production and carcass traits of some pig breeds which are raised in Cambodia, show that the exotic breeds (Yorkshire or Landrace or their crosses) have a higher genetic potential in growth rate, as well as higher lean ratios than local breeds (Hainam, Kondol and Kampot) and F1 crossbreeds between local and exotic pigs. For that reason, protein requirement of F1 pigs as recommended by NIAH (1995) is lower than of exotic breeds recommended by NRC (1998). The quality of a protein depends on its amino acid composition, and a good quality protein should contain all the essential amino acids in proper proportions and amounts. A feed which is imbalanced in amino acid contents, as for low protein diets, is effective in depressing feed intake. In growing pigs, lysine is often the first limiting amino acid, and a serious lack of lysine in diets results in decreased feed intake (Tamminga and Jansman, 1993). The requirement of crossbred fattening pigs for dietary protein according to NIAH (2001) is 16.5% for pigs of 15-50 kg and 13.3% for pigs of 50-80 kg (DM basis).

However, when energy sources low in protein (eg: sugar cane juice, cassava roots, sweet potato tubers or banana fruit) are combined with leaves which normally have well balanced arrays of amino acids, it is possible to reduce the overall level of protein in the diet since the amino acid array in such a combination of feeds will more closely approximate to that in the "ideal" protein (See Wang and Fuller 1989).

The ideal protein is conceived as providing the essential amino acids in the proportions required by the pigs and of having the correct balance between the essential and non-essential amino acids (Speer, 1990).The balance of amino acids in the ideal protein compared with Water spinach and sweet potato vines is in Table 4.

In the present study (Paper I), when the protein source was a mixture of water spinach and sweet potato vines, the growth rate and feed conversion were improved as the protein level was raised, but the relationship between live weight gain and crude protein concentration was curvilinear, indicating there was no improvement in growth rate when the crude protein exceeded 14% in the diet DM.

Energy sources for pigs

Pigs need energy for all of activities such as breathing, heart action, digestion, muscular movement, as well as heat to keep the body warm. If the pigs consume more energy than necessary to carry out these vital functions, the excess is stored as body fat. The main energy sources in the diet are carbohydrates. Cereal grains are widely used in pig feeding because of their very high soluble carbohydrate (60-70%) and low crude fiber contents (Tamminga and Jansman, 1993), and generally make up between 55% and 85% of compounded feeds (Machin, 1992). Another group of energy sources is the fats and oils, which are very concentrated sources of energy. However, the use of cereal grains for animal feed competes with the needs of humans, so it appears that replacement of the cereal component by cheap and locally available roots and tubers is likely to give both economic and other benefits. Roots and tubers have high carbohydrate contents, and thus are rich energy sources. For example, cassava root meal has a carbohydrate content of about 88% (Dominguez, 1985; Ravindran et al., 1982) and sweet potato roots 80-90% (Dominguez, 1992). NIAH (2001) recommended that diets for crossbred fattening pigs (15-80 kg) should contain 13.4 MJ/kg DM of metabolizable energy (ME).

            Broken rice is a good source of carbohydrate for pigs. The paddy rice after milling produces 20% hulls, 10% bran, 3% polishing, 1-17% broken rice and 50-60% polished rice (Göhl,1975). Broken rice has high digestible energy (DE) content of 14.5 MJ/kg according to Farrell and Warren (1982) 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.

            Cassava root meal is a good energy source for pigs but is low in protein. The energy in roots is mainly in the form of starch. Therefore, it might offer considerable potential to furnish a considerable share of the nutrients currently provided by more conventional energy sources for pigs (FAO, 1992). Cassava root meal is usually prepared by chopping the whole root and drying under sunlight for several days before making it into meal. Gómez (1992) reported that piglets from weaning to between 20–25 kg, fed diets containing 20 to 25% cassava root meal, performed similarly or slightly better than those fed a maize-soybean meal ration. 

However, cassava root meal is low in protein and contains cyanogenic glucosides (Loc, 1997; Pérez, 1997). The feeding of more than 50% cassava meal in the ration is reported to decrease the live weight gain and the feed conversion of pigs (Eusebio, 1980). Using ensiled cassava and cassava by-products can replace up to 50% of the cereal by-products (rice bran) in pig diets under smallholder farm conditions according to Ngoan et al. (1996).  Moreover the price of cassava roots and cassava by-products is usually cheaper than that of rice bran and maize (Ngoan et al., 1996).

Normally, the farmers in Cambodia start to fatten pigs after harvesting the rice when the by-products (rice bran) become available. Research work published so far with this by-product shows that it is possible to use about 40% of defatted rice bran in swine feeds without affecting negatively animal performance (Borin et al., 1988). Some 98% of smallholder farms were reported to use rice bran for pig production (Kinh et al., 2002). Rice bran is available in farms after harvesting of rice, especially when milling rice for home consumption and is only stored in small amount due to fast changing quality. However, rice bran has a high crude fibre (8.6-19.6%) and should not be used at levels of over 40% for pig feed (Tran et al., 1985).

In the present study (Paper I), growth rates were the same but feed conversion was better when the energy source was broken rice rather than cassava root meal mixed with rice bran.

Conclusions    

          The use of forages such as water spinach and sweet potato vines in pig feeding can have socio-economic benefits for small scale farmers as these feeds can be easily cultivated and harvested on the farm. Incorporating these two crops in the farming system will also be of benefit to the environment as they can utilize efficiently the waste manure from pigs to produce high biomass yield of superior nutritive content.

          Both broken rice and a mixture of cassava root meal and rice bran were suitable sources of energy to complement the sweet potato and water spinach foliages in diets of growing pigs. Growth rates were the same on both energy sources but feed conversion was better with broken rice.

          Growth rate and feed conversion were improved as the level of protein provided by the combined sweet potato and water spinach foliages was raised, but the relationships were curvilinear, indicating there was no further improvement in growth rate when the crude protein exceeded 14% in the diet DM.

References

An, L V, Frankow-Lindberg  B E, Lindberg, J E, 2003: Effect of harvesting interval and defoliation on yield and chemical composition of leaves, stems and tubers of sweet potato (Ipomoea batatas L. (lam)) plant parts. Fiel