Palm (Elaeis guineensis) oil and cassava foliage as feed resources for growing pigs; a review of the literature

There will be increasing pressure to make use of available feed resources in tropical regions as pressure increases on the supply of traditional animal feeds in the form of cereal grain and protein oilseed meals. There are many by-products and residues in tropical countries which arise from the growing of food crops. There is also the potential for development of new feed resources arising from crops grown as sources of renewable energy (biomass) and trees and shrubs planted to protect the environment. In this category will be the range of products and by-products derived from sugar cane (FAO 1988; Figueroa and Ly 1990; Sarria et al 1990; Perez 1995), African oil palm (Ocampo et al 1990a,b; Ocampo 1992; Ocampo 1994a,b,c), the sugar palm (Borassus flabiller) tree (Khieu Borin et al 1996), multi-purpose trees and shrubs and aquatic plants. Many of these feed resources are rich in available energy (the juice from sugar cane and sugar palm, the oil and fruit from the African oil palm) and in protein (the leaves from multi-purpose trees and aquatic plants). The leaves of most water plants are more digestible than the leaves from trees and generally they appear to have low concentrations of anti-nutritional factors.

The traditional sources of protein in the diets of monogastric animals are the by-products from oilseed milling and the processing of livestock, including fish. There is an urgent necessity to develop protein sources that can be produced and processed on the farm. Although there is scope for the cultivation of traditional protein crops such as soybean, groundnut and sunflower, as components of integrated and associated cropping systems, a more appropriate approach is the growing of trees, shrubs and water plants that produce much higher unit area yields of protein in the form of leaf biomass. Legumes producing protein-rich seeds, such as Canavalia ensiformis and Canavalia gladiata, have received attention from researchers in Africa (Udebibie 1991) and Latin-America (Pound et al 1984) but have had little impact in practice. Strategies to utilize efficiently these unconventional feeds are more likely to succeed when the production system is matched with the available resources (Preston and Leng 1987).

2.0 The nutrient requirements of pigs fed tropical feed resources

The nutritional requirements for pigs reared in tropical regions are different from those in temperate countries. High ambient temperatures can be beneficial in that little energy is needed to maintain body temperature. On the other hand, the negative effect of high ambient temperature is the reduction that occurs in voluntary feed intake (Stahly et al 1979). The use of tropical energy-rich feeds low in protein (eg: sugar cane, cassava roots, sweet potato tubers and palm oil) facilitates meeting requirements for amino acids with lower overall levels of protein in the diet, as compared with temperate country diets based on cereal grains, the protein of which contains many non-essential amino acids, thus requiring higher overall levels of protein to meet the needs of essential amino acids (Preston 1995).

The protein requirements of pigs in temperate countries fed diets based on cereal grains are well documented (eg: NRC 1988; ARC 1980). However, two factors must be taken into account in deciding on the levels of protein that will be appropriate for pig production 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). The second point is that most of the “tropical” energy feeds are low in protein, thus meeting 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 levels used by Sarria et al (1990) for growing pigs fed sugar cane juice and soya bean meal were only 200 g/day, less than 60% of the NRC (1988) standards, yet the median growth rate in 8 on-farm trials was 590 g/day.

3.0 Cassava leaves as a protein source for pigs

3.1 The role of cassava in integrated farming system

Cassava (Manihot esculenta) is widely cultivated in tropical regions of Africa, Latin America and Asia (Calpe 1992). It can adopt to a variety of climatic conditions though a warm and humid climate is preferred. Cassava is a drought-tolerant crop and can grow well in areas, where there are occasionally prolonged spans of drought. It is especially tolerant of infertile soils.

Cassava leaves are a readily available by-product at the time of harvesting the roots, which usually occurs from 6 to 8 months after planting. However, according to Montaldo (1977), cassava plants can withstand defoliation for several years if they receive adequate fertilization and irrigation, and under such management conditions have the potential to produce up to 4 tonnes of protein per hectare, annually. The management of cassava as a forage crop with high levels of fertilization have recently been documented by Preston et al (2000) and Preston (2001). Annual yields of fresh foliage of between 80 and 120 tonnes/ha were recorded during two year periods in Vietnam and Cambodia, with continuous harvesting of the foliage every 2 months, accompanied by heavy fertilization with goat manure or biodigester effluent.

3.2 Cassava leaves as a source of protein

Cassava leaves are rich in protein, the concentration of which appears to vary widely with the variety (Table 1).

Table 1: Chemical composition of some varieties of cassava leaves (Source: Bui Huy Nhu Phuc et al 1996)
	Protein	EE	Fibre	Ash	HCN*	HCN#
	-----------------% of DM-----------				--mg/kg DM--
KM 94	34.7	13.3	12.0	6.2	509	86.3
India	31.0	14.1	11.7	7.8	411	57.6
Gon	28.5	13.5	14.6	7.9	285	17.0
Japan	27.1	14.6	10.1	6.1	347	57.1
KM 60	25.4	14.4	9.70	5.0	490	23.0
KM 95	23.9	15.6	10.7	5.9	360	20.2
*Before sun-drying #After sun-drying

The protein is rich in lysine but slightly deficient in methionine (Eggum 1970). The leaves are a good source of minerals, particularly Ca, Mg, Fe, Mn and Zn (Ravindran and Ravindran 1988). Cassava leaves are also rich in ascorbic acid and vitamin A, and contain significant amounts of riboflavin. But considerable losses of vitamins, particularly of ascorbic acid, may occur during processing (Ravindran 1992). The protein content of the leaves was increased when biodigester effluent was used as fertilizer as compared with the original manure (Le Hau Cha 1998).

3.3 Anti-nutritional compounds in cassava leaves

Anti-nutritional factors are widespread in livestock feeds in the tropics (Makkar 1993). Consumption of feed containing these constituents may lower feed intake, nutrient utilization, feed conversion efficiency and animal performance, with negative economic consequences. The principal anti-nutritional factors in cassava leaves are tannins and precursors of hydrocyanic acid (HCN).

3.3.1. Tannins

Tannins are a diverse group of polyphenolic substances. Tannins have been defined by Van Soest et al (1987) as phenolic compounds of moderately high molecular weight containing sufficient phenolic hydroxyl groups to effectively form strong complexes with proteins and other macromolecules. It is recognized that there are two main types of tannins: the condensed tannins which are isomeric forms of flavonols; the hydrolysable tannins which are esters of sugars and polyhydroxyphenolic acids. These compound have the capacity to lower protein digestibility and amino acid availability either by forming indigestible complexes with dietary protein or by inactivation of proteolytic enzymes (Kumar and Sing 1984). A reduction in feed intake may occur due to the slowdown in the digestion of the feed or to low palatability (Kumar and D’Mello 1995). The content of tannins in cassava leaves increases with maturity and varies between cultivars, in the range of 30 to 50 mg/kg DM according to Ravindran (1993) (see also Table 1).

3.3.2. Cyanogenic glycosides

The cyanogenic glycosides present in cassava leaves cause toxicity to animals when hydrocyanic acid is generated (Van Soest 1994). The glycosides are decomposed by betaglucosidases (Polton 1988; CARB 1997) and hydroxynitrile xylases (Poulton 1988) to form hydrocyanic acid (HCN). Although these enzymes are not present in mammalian tissues, the microflora in the human intestine are able to produce them (CARB 1997). HCN is colourless, volatile and extremely poisonous. HCN is rapidly converted in the body to thiocyanate which is no longer toxic (Hartung 1983). Due to this rapid detoxication, animals are able to ingest amounts of cyanide only slightly less than the lethal dosis over extended periods without apparent harm (Humphreys 1988). Stosic and Kaykay (1981) noted that small quantities of HCN ingested on a regular basis, though not large enough to cause mortality, may be sufficient to affect the general health and productivity of the animal. Other studies showed that cyanides may be associated with malformation and low weight of foetuses (USEPA 1999). In terms of mortality due to HCN, an amount of 2mg/kg of live weight is considered the minimum lethal dose for most species (Clarke and Clarke 1967). According to Humphreys (1988), intake of feeds containing over 20mg HCN/100g are potentially dangerous to stock.

The presence of cyanogenic glucosides could lead to a deficiency of the essential amino acid – methionine – if dietary supply of this amino acid is marginal, with the result of reduced animal performance (Oke 1978). Bitterness associated with the high cyanogenic glucoside content in cassava has been reported in a number of studies (Lee and Hutagulung 1972; Mahendranathan 1971; Sudaresan et al 1987). The cyanide content varies with variety and nutritional status of the plant with values as low as 80 mg/kg DM (Wood 1965) and over 4000mg/kg DM in fresh leaves according to Ravindran and Ravindran (1988). It is increased by N fertilization of the cassava (De Bruilin 1973) but decreases with age (Lutaladio 1984; Ravindran and Ravindran 1988). Simple sun-drying or oven-drying has been reported to eliminate almost 90% (Oke 1994), and is more effective than ensiling because of the stability of the linamarase at low pH values (Oke 1994). Despite the high cyanide levels in cassava leaves, documented cases of poisoning due to the ingestion of cassava leaves are rare (Ravindran 1993).

3.4 Cassava leaves products as alternative protein source for pigs

3.4.1 Fresh cassava leaves

Early studies on the feeding of fresh cassava leaves to pigs (Mahendranathan 1971) showed that palatability was depressed and growth performance was lowered with increasing proportion of leaves in the diet. The adverse effects were evidently due to the high hydrocyanic acid levels in the fresh leaves. In a later study, Sarwat et al (1988) found that inclusion of 15% fresh cassava leaves had no adverse effects on the performance of growing-finishing pigs.

3.4.2 Cassava leaf meal (CLM)

Ravindran et al (1987) evaluated CLM as a substitute for coconut meal. The results showed that CLM could replace up to 66 percent of the coconut meal (26 percent of the total diet) in growing pig diets without adverse effects on performance. Most efficient gains were obtained at 33 percent replacement (13 percent of the total diet). Attempts to utilize CLM as a replacement for other protein supplements in pig diets have been less encouraging. Alhassan and Odoi (1982) reported depressions in live weight gains and feed efficiency when CLM was included at 20 and 30% levels to replace part of the peanut meal, fish meal and maize in the basal ration for growing- finishing pigs. Ravindran (1990) substituted 10, 20 and 30% CLM in a maize-soybean meal basal diet and reported that live weight gain and feed efficiency of growing pigs were lowered linearly with increasing levels of leaf meal. He reported that the performance of pigs on diets containing 10% CLM was improved by adding methionine.

3.4.3 Cassava leaf silage

Ensiling of cassava leaves has been stimulated by the need to reduce the risk of cyanide toxicity, and by the difficulties of sun-drying the leaves when these are harvested in the wet season (Limon 1992; Bui Van Chinh et al 1992; Du Thanh Hang 1998; Bui Huy Nhu Phuc et al 1996; Bui Van Chinh 1990; Ravindran 1990; Chhay Ty et al 2001; Bui Van Chinh and Le Viet Ly 2001).

Bui Huy Nhu Phuc et al (2000, 2001a) and Bui Huy Nhu Phuc and Lindberg (2000) reported that increasing the level of ensiled cassava leaves to replace the protein from conventional sources led to a reduction of feed intake, apparently due to the associated increase in the fibre content of the diet. N balance studies with ensiled cassava leaves in Vietnam showed a general trend to a reduction in N retention with increase in the levels of the silage (Bui Huy Nhu Phuc et al 1996;Nguyen Van Lai and Rodriguez 1998; Du Than Hang 2000). In contrast, Ly and Samkol (2001) in Cambodia included 50% of cassava leaf silage in the diet DM and reported normal feed intakes and N retention. Ly and Rodríguez (2001) suggested that the reason for the better results reported by Ly and Samkol (2001) could be in the nature of the leaves that were used. In the research in Vietnam, the leaves were the by-product obtained at the time of harvesting the root, whereas in the Cambodian research, the leaves were obtained from foliage harvested at 2-month intervals (Preston 2001). This suggestion of Ly and Rodríguez (2001) was the basis of the hypothesis tested in Experiment 2 of this thesis. The results obtained by comparing silage made from two ages of leaves proved that the young leaves (from 2-month regrowth) were more digestible and supported higher N retention in growing pigs than the old leaves (harvested 5 months after planting).

4. Palm oil for feeding pigs

In most developing countries, the major energy sources in pig diets are maize, cassava root meal and rice by-products. Little consideration has been given to the products and by-products of the African oil palm, despite the fact that this tree is highly productive and well adapted to humid tropical ecosystems (Ocampo et al 1990 and 1994; Gohl 1992). A potential advantage from using palm oil as an energy source is its high caloric value and the absence of fibre. This creates opportunities for making greater use of unconventional sources of protein for pigs such as tree leaves and water plants (Preston and Murgueitio 1992), which are high in fibre and of low energy value.

4.1. The role of oil palm in integrated farming systems

The oil palm is traditionally managed as a plantation crop for the production of cooking oil. An alternative approach put forward by Ocampo (1996) is to consider the oil palm as a component of an integrated farming system in association with a range of other tree crops such as sugar cane, cassava and multi-purpose trees. In this case the fruit of the oil palm would be the basic diet of pigs, which are the species with greatest capacity to extract the oil from the fruit. The fibrous residues left by the pigs could be offered to cattle and horses, while the nuts that are not broken by the pigs could be recovered and cracked and fed to hens. The manure produced by the animals is used for the production of biogas, and as a source of organic fertilizer for the crops or for the manufacture compost.

4.2. Palm oil as source of energy for pigs

Palm oil has been used as an ingredient in animal feed research for more than two decades (Roy et al 1973; Fetuga et al 1975). However, interest in this feed resource has intensified following the demonstration by Ocampo (1994) that it could be fed at up to 50% of the diet, replacing completely sorghum grain as the energy source for growing pigs. This was also the first attempt to introduce protein-rich leaves from a water plant (Azolla filiculoides) as partial replacement (30%) for soya bean protein. Live weight gains were: 526, 561, 535 and 452 g/day with DM feed conversions of 2.1, 1.98, 2.0 and 2.2 for protein replacement levels of 0, 10, 20 and 30%, respectively. Le Duc Ngoan and Sarria (1993) compared raw palm oil with sugarcane juice as the only energy sources in diets for growing pigs. Growth rates for 0, 25, 50, 75 and 100% replacement of sugar cane juice with palm oil were: 772, 695, 672, 630 and 608 g/day and DM feed conversions: 2.33, 2.33, 2.33, 2.30, 1.98, respectively. There were no negative effects on carcass quality even with 100% substitution of the sugar cane juice by the palm oil.

The hypothesis that was tested in Experiment 3 of this thesis was that adding up to 15% palm oil as replacement for broken rice, in a diet in which ensiled cassava leaves provided 45% of the diet DM, would lead to improvements in pig performance. In fact, the results showed that there were no differences in growth rate nor in feed conversion among any of the treatments, leading to the conclusion that broken rice and palm oil were equally suitable energy supplements in a diet based on ensiled cassava leaves, and that energy density was not a constraint to pig performance in this situation.

4.3 Whole palm fruit

The use of whole palm fruit as an energy source relates to a situation in which the oil palm tree is part of an integrated farming system, as suggested by Ocampo (1996), as opposed to its use as an industrial crop for oil production. The composition of the fruit is (% DM basis): oil 28, crude protein 9, crude fibre 26. In an experiment to evaluate the whole fruit as a replacement for sorghum grain (Ocampo 1994a), the average live weight gains were 625, 598, 503 and 466 g/day over the overall fattening period (25 to 90 kg) for the four levels of substitution (25, 50, 75 and 100%) of sorghum grain. Feed conversion rates (DM basis) were: 3.2, 3.2, 3.3 and 3.4.

The potential value of the whole palm fruit was confirmed in a subsequent experiment (Ocampo 1994b) in which four levels of rice polishings (125, 225, 325 and 425 g/day) were included in the basal diet of ad libitum whole palm fruit and restricted protein (200 g/day) from soya bean meal. Growth rates were: 0485, 515, 492 and 497 g/day with DM feed conversions of 3.2, 3.2, 3.3 and 3.3, respectively. The consumption of whole fruit was 1.1, 1.1, 1.0 and 0.9 kg/day, respectively.

In both experiments it was observed that the pigs easily extracted the oil (and other nutrients) from the fleshy part of the fruit as well as from the kernel, with no need for prior processing. There thus appear to be excellent prospects for using oil palm fruit in pig nutrition, in an integrated production system, as an alternative to the industrial extraction process.

5. Oil palm cultivation in the world

The oil palm (Elaeis guineensis) originated in Africa where groves of wild palm still exist. Cultivated varieties are now grown, however, on plantations in the equatorial tropics in South-east Asia and South Ameria as well as in Africa. The early researchers of some 150 year ago believed that the oil palm oil would be a more useful producer of oil than the coconut palm (Hartley 1988). The oil palm is cultivated in four continents and in over 20 countries, with production strongly concentrated in Southeast Asia, in particular in Malaysia and Indonesia where the operating environment has been very favourable (Table 2).

Table 2. World production of palm oil 1994-2000 (‘000 tonnes )
Countries	1994	1995	1996	1997	1998	1999	2000
Malaysia	7403	7221	8386	9069	8320	10554	10842
Indonesia	3421	4008	4540	5380	5100	6250	6900
Nigeria	645	640	670	680	690	720	740
Colombia	323	353	410	441	424	501	524
Cote D lvoire	310	300	280	260	275	282	292
Thailand	297	316	375	390	405	495	560
Papua New Guinea	223	225	272	275	215	264	296
Equador	162	178	188	203	200	230	215
Costa Rica	84	90	109	119	115	110	113
Honduras	80	76	76	77	88	80	78
Brazil	54	71	80	80	89	93	97
Venezuela	21	34	45	54	54	68	81
Guatemala	16	22	36	50	47	52	58
Other	1265	1676	815	825	822	863	934
Total	14304	15210	16282	17903	16844	20562	21730
Source: Oil world Annual 2000, 1999, 1998 & Oil world weekly 30 March 2001

The average yield of oil palm is estimated at 20 tonnes/ha/yr of fresh fruit bunches (Espinal 1986; Garza 1986), which are capable of producing between 3 to 5 tonnes/ha of crude oil from the fruit (mesocarp) and an additional 0.6 to 1.0 tonne/ha from the palm kernels (Ocampo et al 1990a). It’s productivity is influenced by climate, soil type, genetic factors, maturity, rainfall, fertilization and the harvest period with potential yields of up to 45 tonnes per ha of fresh fruit bunches and 17 tonnes oil per ha (Soh et al 1994). The oil palm yields more oil per unit area than any other crop traditionally used for oil production (Table 3).

Table 3. Comparative yields for various oil crops
Crop	Product	Average oil content (%)	Average yield (tonnes/ha)	Yield of Oil (tonnes/ha)
Oil palm	Fruit	20	20.0	4.00
Oil palm	Kernel	44	1.14	0.54
Soya bean	Seed	17	1.68	0.32
Groundnut	Seed	32	1.21	0.20
Cotton seed	Seed	16	0.99	1.58
Rape seed	Seed	35	1.03	0.48
Sun flower	Seed	35	1.21	0.49
Coconut	Copra	64	1.11	0.35
Source: Ong et al 1991

6. Oil Palm plantation in Cambodia

The oil palm plantation in Cambodia belongs to a private company (Mong Reththy Investment Cambodia Oil Palm Co., Ltd), which was contracted by the Ministry of Agriculture, Forestry and Fisheries in 1996 to invest and develop an oil palm plantation with processing facilities in Prey Nop district, Sihanouk Ville, Kingdom of Cambodia. The projected area for oil palm cultivation is 11000 ha. Until now the Company has been cultivating the oil palm on 3700 ha. The most obvious benefit arising from the establishment of a large oil palm plantation in Cambodia is the substantial level of rural employment which has been created, At the present time, the source of labour (2000 harvesters) for the oil palm plantation is from surrounding villages and the company has donated an area of land within the plantation for the establishment of Khmeng Wat (childrens’ live-in pagoda) village which has already increased to the considerable size of 307 families (1679 persons), which reduces poverty and raises living standards in the district. Beside this, the company has provided on the estate, a hospital, road, school and in-house training for numerous local graduates.

7. References

Abu A A, Okai D B and Tuah A K 1984 Oil palm slurry (OPS) as a partial replacement for maize in the diets of growing-finishing pigs. Nutrition Reports International 30(1): 121-127

Alhassan W S and Odoi F 1982 Use of cassava leaf meal in diets for pigs in the humid tropics. Tropical Animal Health and Production 14: 216-218

Balogun O O, Fetuga B L and Oyenuga V A 1983 The response of the muscles of weanling large white x Landrace pigs to methionine and palm oil supplementation to cassava flour- soybean meal diet. J.Agric.Sci, Camb. (1983). 101, 757-762

Baskin S I and Brewer T G 1997 Cyanide poisoning. In: Sidell, F.R., Takafuji, E.T., Franz, D.R. (Eds), Medical aspect of chemical and biological warfare. Walter Reed Army Medical Center, Washington, D.C pp. 271-286

Babjee A M, Serlan M Z and Hussein H 1991 Palm kernel cake in cattle feedlot ting. ASEAN Food J. (Malaysia). 1991. v. 6(3):102-103.

Becerra M 1991 Azolla-Anabaena; un recurso valioso para la produccion agropecuaria en el tropico. Serie de Manuales Tecnicos# 1 pp1-53

Bui Van Chinh, Le Viet Ly, Nguyen Huu Tao and Do Viet Minh 1992 "C" molasses and ensiled cassava leaves for feeding pigs. Results of research 1985-1990. Agricultural Publishing House, Hanoi. pp: 46.

Bui Van Chinh 1990 The study of ensiling of cassava leaves and top. In: Development of Animal production in mountainous areas on North Vietnam. Hanoi pp 4-7

Bui Van Chinh and Le Viet Ly 2001 Studies on the processing and use of cassava tops as animal feed .pp.94 http://www.mekarn.org/sarpro/chin.htm

Bui Huy Nhu Phuc 1994 Effect of protein supply in sugar cane juice based diets for growing pigs. MSc Thesis Swedish University of Agricultural Science. Uppsala 1994

Bui Huy Nhu Phuc, Preston T R, Ogle B and Lindberg J E 1996 The nutritive value of sun dried and ensiled cassava leaves for growing pig. Livestock Research for Rural Development 8(3) http://cipav.org.co/lrrd/lrrd8/3/bui.htm.

Bui Huy Nhu Phuc, Ogle B and Lindberg J E 2000 Effect of replacing of soybean meal

with cassava leaf protein in cassava root meal based diets for growing pigs on digestibility and N retention. Anim. Feed Sci. Technol. 83: 223-235

Bui Huy Nhu Phuc, Lindberg J E, Ogle B and Thomke S 2001 Nutritive evaluation with rats of tropical biomass products for monogastrics: 1. Comparison of eight green products evaluated at two levels of inclusion in relation to a casein diet. Asian-Aust. J. Anim. Sci. (In press).

Bui Huy Nhu Phuc and Lindberg J E 2000 Ileal and total tract digestibility in growing pigs fed cassava root meal diets with inclusion of cassava leaves, leucaena leaves and groundnut foliage. Asian-Aust. J. Anim. Sci. (In press).

Calp C 1992 Root, tubers and plantains: recent trends in production trade and use. In: Machin D, Nyvold S (Ed.), Root, tuber, Plantains and Bananas in Animal Feeding. FAO Animal Production and Health Paper 95, pp. 11-25

CARB 1997 Cyanide compounds (online). California Air Resource Board. Available from: http://www.arb.ca.gov/toxics/tac/factshts/cyanidec.pdf

Chhay Ty, Ly J and Rodriguez Lylian 2001 An approach to ensiling conditions for preservation of cassava foliage in Cambodia. Livestock Research for Rural Development 13(3): http://www.cipav.org.co/lrrd/lrrd13/3/chhayty

Clarke E G C and Clarke M L 1967 Garner’s Veterinary Toxicology, 3^rd ed. Williams & Wilkins, Baltimore

Cunha T J 1977 Swine feeding and nutrition. pp 154 and 241

Collingwood J G 1958 Palm Kernel meal. In: Processed Plant Protein Foodstuffs Ed: A. M. Altschul, Academic Press, New York pp 995

De Bruilin G H 1973 The cyanogenic character of cassava. In Chronic cassava toxicity. Proc. of the inter. workshop, London. pp. 43-48

Delgado C, Rosegrant M, Steinfeld H, Ehui S and Courbois C 1999 Livestock to 2020: The next food revolution. Food, Agriculture and the Environment Discussion Paper No 28. International Food Policy Research Institute, Washington, DC.

Devendra C and Hew V F 1977 The utilization of varying levels of dietary palm oil by

growing finishing pigs. MARDI Res. Bull. 4. pp 76–87

Devendra C, Yeoung S W and Ong H K 1981 The potential Value of Palm Oil Mill Effluent (POME) as a feed resource For Farm Animal in Malaysia. proc. of National Workshopon Oil palm by-product utilization December 14-15 Kuala Lumpur.

Du Thanh Hang, Nguyen Van Lai, Rodríguez Lylian and Ly J 1997 Nitrogen digestion and metabolism in Mong Cai pigs fed sugar cane juice and different foliages as sources of protein. Livestock Research for Rural Development (9) 2:45-49

Du Thanh Hang 2000 Digestibility and nitrogen retention in fattening pigs fed different levels of ensiled cassava leaves as a protein source and ensiled cassava root as energy source. In: marking better use of local use feed resource (T.R Preston and R B Ogle, editors).

http://www.mekarn.org/sarpro/hang.htm

Du Thanh Hang 1998 Ensiled cassava leaves and duckweed as protein sources for fattening pigs on farms in Central Vietnam. Livestock Research for Rural development 10(3) http://cipav.org.co/lrrd/lrrd10/3/hang 103.htm

Duc N V, Kinghorn B P and Graser H U 1997 Studies on some production and Carcass traits of Mong cai and their crosses in North Vietnam. Proceeding of the Association for the Advancement of Animal breeding and Genetics 12, 185-188

Elson C E 1992 Critical Reviews in Food Science and Nutition. 31:79-102

Eggum O L 1970 The protein quality of cassava leaves. British Journal of Nutrition (24) :

761-769

Espinal M 1986 Informe de la Coordinacion Nacional Tecnica en Palma Africana. En: IV Mesa Redonda Latinoamericana sobre Palma Aceitera, Valledupar, Colombia 8-12 de junio de 1986, ORLAC/FAO p 31-34.

FAO 1988 Sugarcane as feed. FAO Animal Production and Health Paper No. 72 (Editors: R. Sansoucy, Aarts G and Preston T R), FAO, Rome

FAO 1992 Roots, tubers, plantain and banana in animal feeding. ((D. Machin and S. Nyvold, editors). Animal Production and Health paper No 95. Rome. pp 289.

Fetuga B L, Babatunde G M and Lyenuga V A 1975 The effect of varying the level of palm oil in a constant high protein diet on performance and carcass characteristics of the growing pig. E. Afric. for. I., 40. pp 264–270

Figueroa V and Ly J 1990 Alimentacion porcina no convencional. Colección GEPLACEA, Serie DIVERSIFICACION: Mexico pp 215

Garza E F 1986 Situacion actual de la palma aceitera en Mexico. En: IV mesa Redonda latinoamericana sobre Palma Aceitera, Valledupar, Colombia 8-12 de junio de 1986, ORLAC/FAO p 35-36

Gomez G and Valdivieso M 1984 Cassava for animal feeding: effect of variety and plant age on production of leaves and roots. Animal Feed Science and Technology 11: 49-55

Gohl B 1992 Tropical feeds. FAO Tropical feeds database. V.3.

Hartung R 1983 Cyanides and nitriles. In: Clayton, G.D; Clayton, F.E. (Eds), 3rd ed. Patty’s industrial hygiene and toxicology. John Eiley and Sons, Inc., New York.

Hartley C W S 1988 The oil palm. Longman. London

Hertrampf J W 1989 The oil palm-supplies of feedstuffs. Kraftfutter (Germany). 1989. v.72 (11): 386-387

Humphreys D J 1988 Veterianry Toxicology, 3^rd ed. Bailliere Tindall, London.

Hutagalung R I, Mohd-Mahyudin and Syed-Jaludin 1981 Feed for farm animals from the oil palm. Proc. of the Inter. Conference on Oil palm in Agr. in the Eighties. v.2 Kuala Lumpur (Malaysia). 1982. 609-622.

Khieu Borin, Preston T R and Lindberg J E 1996 A study on the use of the sugar palm tree (Borassus flabellifer) for different purposes in Cambodia

Kumar R and D’Mello J P F 1995 Anti nutritional factors in forage legumes. In: Tropical legumes in Animal Nutrition (Eds): D’Mello, P F and Devendra C CAB. International, wallingford, UK. pp. 95-133. quoted from international workshop current research and development on use of cassav as animal feed. Khon Kaen University, Thailand. July23-24, 2001 http://www.mekarn.org./prockk/ly.htm

Kumar R and Singh M 1984 Tannins, their adverse role in ruminant nutrition. J. Agric Food chem.. 32: 447-453

Le Duc Ngoan and Sarria P B 1993 Effect of replacing sugar cane juice with palm oil on growth performance of growing-finishing pigs. Paper presented in the seminar on Sistemas Agrarios Sostenibles para el Desarrollo Rural en el Tropico. Villavicencio, Colombia. Jul. 28-31, 1993

Le Ha Chau 1998 Biodigester effluent versus manure, from pigs or cattle, as fertilizer for production of cassava foliage (Manihot esculenta).. Livestock Research for Rural Development. 10 (3): http://www.cipav.org.co/lrrd/lrrd10/3/chau1.htm

Lee K C and hutagalung R I 1972 Nutrition value of tapioca leaf for swine. Malays. Agric. Res. 2: 38-47

Limon R L 1992 Ensilage of cassava products and their use as animal feed. In: Roots, tubers, plantains and bananas in animal feeding (Editors: D Machin and A W Speedy). FAO Animal Production and Health. Paper No 95:99-110

Liang J B, Abdul-Rahman-Shah, Abdul-Wahab-Yusof and Pathmasingham M 1992 The effect of various feeding regimes and management on the productivity of swamp buffaloes in oil palm estates. Malaysian Agr. J. 1982. v. 53(4): 277-282.

Lumpkin T A and Plucknett D L 1982 Azolla as a green manure; use and management in crop production. Series No 15, pp230, Westview Press; Boulder, Colorado, USA.

Lutaladio N B 1984 Evaluation of cassava clones for leaf production in Zaire. In: Tropical

Root crops: Production and uses. Africa (Eds. E.R. Terry, E.V. Doku, O.B. Arene and N.M. Mahungu). Inter. Develop. Res. Centre, Ottawa. pp 41-44

Ly J and Samkol P 2001 The nutritive value of ensiled cassava leaves for young Mong Cai pigs fed high levels of protein. Livestock Research for Rural Development (13) 4: http://www.cipav.org.co/lrrd/lrrd13/4/ly134b.htm

Makkar H P S 1993 Anti-nutritional factors in foods for livestock. Animal Production in Developing Countries. Br. Soc. Anim. Prod. 16: 69-85.

Mahendranathan T 1971 The effect of feeding tapioca (Manihot utilissima Pohl) leaves to pigs. Malays.Agric. J. 48: 60-68. quoted from international workshop current research and development on use of cassav as animal feed. Khon Kaen University, Thailand. July23-24, 2001 http://www.forum.org.kh/~mekarn/proc-cass/ly.htm

Montaldo A 1977 Whole plant utilization of cassava for animal feed. In: Cassava as animal feed (Editors: B Nestel and M Graham) IDRC O95e. Ottawa pp:95-106

Ngo Huu Toan 2003 Comparison between Mong Cai and Exotic pigs in response to Protein Levels on Growth Performance, Digestibility and N-Retention in central Vietnam. Proceedings National Seminar-Workshop on Sustainable Livestock Production on Local Feed Resources. MEKARN, Hue University of Agriculture and Forestry, March 2003

Nguyen Van Lai and Rodriguez L 1998 Digestion and metabolism in Mong Cai and large white pigs having free access to sugar cane juice or ensiled cassava root supplement with duckweed or ensiled cassava leaves Livestock Research for Rural Development 10(2). http://cipav.org.co/lrrd/lrrd10/2.lai.htm

NRC 1988 Nutrient requirement for swine. National Academy Press; Washington, DC

Ocampo A D 1992 Oil-rich fibrous residue from African oil palm as basal diet of pigs: effects of supplementation with methionine. Livestock Research for Rural Development. 4 (2): 55-59

Ocampo A D, Lozano E and Reyes E 1990a Utilization de la cachazade palma Africana

como fuente de energia en el levante, desarollo y ceba de credos. Liv. Res.for Rural Development. 1990. 2(1):43-50

Ocampo A, Castro C and Alfonso L 1990b Determinacion del nivel optimo de proteina al utilizar cachaza de palma africana como fuente de energia en raciones para cerdos de engorde. Livestock Research for Rural Development (2) 2:67-76

Ocampo A 1994a Raw palm oil as the energy source in pig fattening diet an azolla filiculoides as a substitute for soya bean meal. Livestock research for rural development, Vol. 6, No. 1.

Ocampo A 1994c Efecto del nivel de pulidura de arroz en una dieta basada en el fruto entero

de palma africana para el engorde de cerdos. Livestock Research for Rural Development (6) 2:(18Kb)

Ocampo A 1995 In: Proceedings of First International Symposium on the Integration of Livestock to Oil Palm. pp. 87-91

Ocampo A 1996 The African Palm in integrated farming system in Columbia: New developments. In ( Second electronic FAO Electronic Conference on Tropical Feeds Livestock Feed Resource within Integrated Farming System). Food and Agriculture Orgaization of united Nation, FAO. http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAP/FRG/conf96.htm/ocampo.htm

Ong, Hamirin and Chow 1991 In:Proceedings of world conference on Oleochemicals into

the 21st Century, Kuala Lumpur. AOCS: Champaign, III.

Odreman B and Pena M 1987 Crude African palm ( Elaeis guineensis) oil in diets for fattening chickens. informe annual, universidad central de Venezuela, Facultad de Agronomia, Instituto de Produccion Animal, 1987, 61-64

Oke O L 1994 Eliminating cyanogens from cassava through processing: Technology and tradition. In: Acta Horticulturea Cassava Safety 375. Proc. Int. Workshop in Nigeria. pp. 163-174

Oke O L 1978 Problems in the use of cassava as animal feed. Anim. Feed Sci. Technol. 3:

345-380

Omole T A and Onwudike O O 1983 Effect of palm oil on the use of cassava peel meal by rabbits Trop. Anim. Prod. 1983. 27-32.

Perez R 1995 Feeding pigs in the tropics. FAO Animal Production and Health Paper. FAO, Rome.

Preston T R and Leng R A 1987 Matching Ruminant Production Systems with Available resources in the Tropic and Subtropics. PENAMBUL Books Ltd: Armidale NSW, Australia.

Preston T R and Murgueitio E 1992 Strategy for sustainable livestock production in the tropics. Condrit Ltda, Cali Colombia pp 89

Preston T R, Rodriguez Lylian and Khieu Borin 2000 Associations of cassava and legume trees as perennial forage crops for livestock. Workshop-seminar “ Marking better use of local feed resources “ January 2000. SAREC-UAF (Editors: TR Preston and R B Ogle). UAF, Ho Chi Minh City, Vietnam

Preston T R 2001 Potential of cassava in integrated farming systems. . International Workshop Current Research and Development on Use of Cassava as Animal Feed, Khon Kaen, Thailand July 23-24, 2001. http://www.forum.org.kh/~mekarn/proc-cass/ly.htm

Poulton J E 1988 Localization and catabolism of cyanogenic glycosides. In: Evered, D., Harnett, S., Ciba foundation symposium on cyanide compounds in biology, 15-17 March 1988, London. John Wiley & Sons Ltd, Chichester 140, pp. 67-91

Pound B, Done F and Peralta C 1984 Effect of cutting frequency on seed and forage yield of Canavalia ensiformis (L) D C (Jack bean). Tropical Animal Production. 7: 272-276

Preston T R 1995 Tropical Animal Feeding. APHP126, FAO Rome

Ravindran V, Kornegay E T, Rajaguru A S B and Notter D R 1987 Cassava leaf meal as a replacement for coconut oil meal in pig diets. Journal of the Science of Food and Agriculture 41: 45-53

Ravindran V and Ravindran G 1988 Changes in the nutritional composition of cassava (Manihot esculenta Crantz) leaves during maturity. Food Chemistry (27): 299-309

Ravindran V 1990 Feeding value and digestibility of cassava leaf meals for growing pigs. Proceedings Fifth Australasian Animal Production Congress. Volume 3: 20.

Ravindran V 1992 Preparation of cassava leaves product and their use as animal feeds. In: Roots, tubers, plantains and banana in animal feeding. (Editors: D Machin and AW Speedy). FAO Animal Production and Health Paper No. 95. FAO: Rome pp 111-126