Effect of replacing soybean protein with cassava
leaf protein in cassava root meal based diets for
growing pigs on digestibility and N retention
Bui Huy Nhu Phuc
a, B. Ogle
b, J.E. Lindberg
b,* aUniversity of Agriculture and Forestry, Department of Animal Nutrition, Thu Duc,Ho Chi Minh City, Viet Nam
bSwedish University of Agricultural Sciences, Department of Animal Nutrition and Management,
P.O. Box 7024, S-750 07 Uppsala, Sweden
Received 16 April 1999; received in revised form 20 September 1999; accepted 18 November 1999
Abstract
The nutrient and HCN contents of cassava leaves from six varieties of cassava growing in south Viet Nam were analysed and three balance experiments were performed with growing pigs to evaluate the digestibility and nitrogen utilisation of cassava root meal based diets with increasing levels of replacement of the protein from soybean meal (SBM) by the protein of cassava leaves. In Experiment 1 cassava leaf meal (CLM) replaced SBM in the proportions 0, 0.35, 0.70 and 1.00 of the crude protein (CP); in Experiment 2 ensiled cassava leaves (ECL) replaced SBM in the proportions 0, 0.15, 0.30 and 0.45 of CP and in Experiment 3 CLM replaced SBM in the proportions 0, 0.15, 0.30 and 0.45 of the CP.
The CP contents of the cassava leaves ranged from 240 to 350 g/kg, and the crude ®bre (CF) contents from 100 to 150 g/kg on a dry matter (DM) basis. The HCN content was markedly reduced by both sun-drying and ensiling, with the reduction being higher after sun-drying.
The apparent digestibilities of organic matter (OM), CP, ether extract and CF decreased linearly (P<0.001) with increasing levels of inclusion of cassava leaves in the diet. The amount (g/day) of total nitrogen retained and the proportion of nitrogen utilised (proportion of N digested) decreased (P<0.001) with increasing levels of inclusion of cassava leaves in the diet. The digestibility coef®cients of OM, CP and CF were calculated to be 0.49, 0.51 and 0.44 and 0.52, 0.51 and 0.59 in CLM and ECL, respectively.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Cassava leaf meal; Ensiled cassava leaves; Digestibility; Nitrogen utilization; HCN; Pigs
*Corresponding author. Tel.:46-18-67-21-02; fax:46-18-67-29-95.
E-mail address: jan-eric.lindberg@huv.slu.se (J.E. Lindberg).
1. Introduction
Cassava (Manihot esculenta Crantz) is a widely grown crop in most countries in the tropical regions of Africa, Latin America and Asia, and ranks as one of the main crops in the tropical countries (Calpe, 1992). Cassava is extremely reliable to grow, especially on sloping rain-fed soils of low fertility, survives drought periods and grows well with limited supplies of water. In addition, it is tolerant of acid soils and yields well on marginal soils without excessive use of costly inputs. These qualities have endeared cassava to resource-poor farmers. Furthermore, it is a readily available product at the time of harvesting the roots. However, in the rainy season it is dif®cult to sun-dry, and extending the drying period diminishes the nutritional quality of the product. Ensiling could be a suitable alternative way of preserving the leaves.
In view of the predicted world shortage of cereal grains because of competing needs for the expanding human population, the availability and supply of grains and protein feedstuffs is likely to become more limited (Close, 1993), and more research into the use of non-conventional sources of energy and protein for livestock production has been called for. Numerous reports have shown that cassava leaf has a high but variable protein content (170±400 g/kg on a dry matter basis), with almost 0.85 of the crude protein fraction as true protein (Ravindran, 1993). While cassava leaf protein is low in sulphur amino acids (Gomez and Valdivieso, 1984), the content of most other essential amino acids is higher than in soybean meal (Eggum, 1970).
The aim of the present work was to determine the nutritive value for growing pigs of sun-dried and ensiled cassava leaves by replacing the protein of soybean meal with protein from cassava leaves in cassava root meal based diets. Samples of cassava leaves from varieties growing in south Viet Nam were also analysed for nutrient and HCN contents.
2. Materials and methods
2.1. Collection and treatment of cassava leaves
Leaves were collected from six cassava varieties grown at different sites in south Viet Nam from 3 to 4 months after planting. The leaves were sun-dried and samples taken for chemical analysis. Sun-drying consisted of spreading the leaves on the ground and turning them over while exposed to the sun during a 1±2 day period. The dried leaves were then ground and passed through a 2 mm sieve. For ensiling the leaves were chopped into small pieces (about 5 cm long) and mixed with molasses (50 g/kg on a fresh weight basis) and 5 g/kg by weight of salt prior to storage in 50 l containers. The contents were pressed and air removed with a vacuum pump prior to sealing, and were stored for 6 weeks at room temperature (28±328C) before being fed to the pigs.
2.1.1. Experiment 1
tract nutrient digestibility in cassava root meal based diets with inclusion of sun-dried cassava leaf meal (CLM). The CLM replaced soybean meal in the proportions 0, 0.35, 0.70 and 1.0 of the crude protein (CP) in the diets, which were based on cassava root meal. The dietary ingredients and chemical composition are given in Table 1. The overall protein level was restricted to 110 g/kg of the diet (dry matter basis) to ensure that this nutrient would be in limited supply.
2.1.2. Experiment 2
Eight castrated male pigs (Large WhiteLandraceDuroc) with an initial BW of about 30 kg (SD 3) were used in a double Latin-Square design to study nitrogen balance and total tract nutrient digestibility in cassava root meal based diets with inclusion of ensiled cassava leaves (ECL).
As results from Experiment 1 indicated lower intakes of the diets with 0.70 and 1.00 of the CP replacement, ECL replaced soybean meal in the proportions 0, 0.15, 0.30 and 0.45 of the CP in the basal diet. The dietary ingredients and their chemical composition are shown in Table 2.
2.1.3. Experiment 3
Eight castrated male pigs (Large WhiteLandraceDuroc) with an initial BW of about 50 kg (SD 5) were used in a double Latin-Square design to study nitrogen balance and total tract nutrient digestibility in cassava root meal based diets with inclusion of
sun-Table 1
Dietary ingredients (g/kg DM) and chemical composition (g/kg DM) of cassava leaf meal (CLM) and diets in Experiment 1
CLM Proportion of dietary CP from CLM
0 0.35 0.70 1.0
Ingredients
Cassava root meal 770 700 630 570
Soybean meal 200 130 60 0
Cassava leaf meala 0 140 280 400
Salt 5 5 5 5
Bone meal 25 25 25 25
Premixb 0.5 0.5 0.5 0.5
Chemical composition
Crude protein 275 112 113 111 108
Ether extract 125 20 29 36 48
NFE 418 772 736 710 691
Crude ®bre 155 41 55 74 83
NDF 320 97 122 147 168
Ash 82 55 67 69 70
aHCN: in fresh material 251 mg/kg and after sun-drying 20 mg/kg. bComposition per kg: Vitamin A: 72,000,000 IU; D
3: 10,800,000 IU; E: 15,000 IU; K3: 5000 mg; B1:
2000 mg; B2: 15,000 mg; Calcium pantothenate: 25,000 mg; Niacin: 30,000 mg; B12: 30 mg; Folic acid:
dried CLM. As in Experiment 2, CLM replaced soybean meal at levels of 0, 0.15, 0.30 and 0.45 of the CP in the basal diet. The dietary ingredients and their chemical composition are shown in Table 3.
2.2. Feeding, and collection of faeces and urine
The experimental periods lasted 12 days, the ®rst 7 days for adaptation to the diet and the last 5 days for total collection of faeces and urine. During the adaptation period pigs were kept in pens with concrete ¯oors without bedding material, and were moved to metabolism cages for collection of excreta.
Feed was offered ad-libitum during the adaptation period and restricted during the experimental period to ensure that feed intake would be constant at the level consumed by the pigs fed the least palatable diet. The diet was offered in equal amounts three times daily (07:30, 10:30 and 15:30 hours). For all ECL diets, the ensiled leaves were fed separately in quantities corresponding to their content in the diet adjusted to the daily amount of feed consumed by the pigs fed the control (zero ECL) diet. During the experimental period feed offered and refusals were weighed daily.
Urine was collected in a container with 5% H2SO4solution to maintain the pH below 4. All the faeces and an aliquot of 10% of the urine were collected daily and stored in a freezer atÿ188C until the end of the experiment. At the end of the collection period samples of faeces and urine were mixed thoroughly and representative samples were taken for chemical analysis.
Table 2
Dietary ingredients (g/kg DM) and chemical composition (g/kg DM) of ensiled cassava leaves (ECL) and diets in Experiment 2
ECL Proportion of dietary CP from ECL
0 0.15 0.30 0.45
Ingredients
Cassava root meal 740 703 660 690
Soybean meal 234 199 164 129
Ensiled cassava leavesa 0 72 144 216
Salt 5 5 5 5
Bone meal 20 20 20 20
Premixb 1 1 1 1
Chemical composition
Crude protein 276 127 133 135 137
Ether extract 139 22 29 38 46
NFE 311 789 765 740 716
Crude ®bre 171 31 40 50 59
NDF 335 102 117 130 149
Ash 103 31 33 37 42
2.3. Chemical analysis
Feed and faeces samples were oven dried and then milled through a 1 mm screen prior to analysis. Chemical analyses of feed and excretion products were performed according to A.O.A.C. (1980). Dry matter (DM) was determined at 1058C overnight, ash at 5008C, crude protein (CP; N6.25) by a conventional macro-Kjeldahl method on fresh samples and ether extract (EE) was determined by Soxhlet extraction, without prior acid hydrolysis. Neutral detergent ®bre (NDF) was analysed according to Robertson and van Soest (1977). The HCN was determined by titration with 0.1N AgNO3after boiling the sample and concentrating the HCN in KOH (A.O.A.C., 1980).
2.4. Statistical analyses
Regression analyses were performed using (Minitab (1994) Version 9) to evaluate the effects on digestibility and nitrogen retention of the inclusion of cassava leaf protein. The digestibilities of the nutrients in CLM and ECL were estimated with the linear regression analysis procedure in Minitab (Version 9, 1994). For digestibility the amounts of nutrients from CLM and ECL replacing nutrients in soybean meal were used as independent variables and digested amounts of nutrient as dependent variables using the model:
Y b0b1x1b2x2
whereb0is equal to intercept, x1 to nutrient in basal diet (g),x2to nutrient in cassava leaves (g),b1to digestibility coef®cients of nutrients in the basal diet andb2is equal to digestibility coef®cients of nutrients in cassava leaves.
Table 3
Dietary composition (g/kg DM) and chemical composition (g/kg DM) of cassava leaf meal (CLM) and diets in Experiment 3
CLM Proportion of dietary CP from CLM
0 0.15 0.30 0.45
Ingredients
Cassava root meal 770 735 700 665
Soybean meal 200 170 140 110
Cassava leaf meala 0 65 130 195
Salt 5 5 5 5
Bone meal 25 25 25 25
Premixb 1 1 1 1
Chemical composition
Crude protein 260 113 113 116 113
Ether extract 99 27 32 36 39
NFE 371 781 763 746 733
Crude ®bre 161 27 35 41 51
NDF 335 97 110 123 136
Ash 109 52 57 61 64
3. Results
3.1. Chemical composition of cassava leaves
The chemical composition of six varieties of sun-dried cassava leaves is shown in Table 4. On a DM basis the CP contents were very variable and rather high (239±347 g/ kg), and the CF contents also varied considerably between the varieties (97±146 g/kg). The cassava leaf meals used in Experiments 2 and 3 were from a mixture of leaves of several varieties and had CP contents that were midway in the range of values determined in the ®eld (Tables 2 and 3).
The contents of HCN also varied between the varieties, from 285 to 509 mg/kg DM, and in Experiment 1 were reduced on average by 90% by sun-drying. There was an indication of an increased content of HCN with increasing protein content of the leaves (r0.344). After 6 weeks of ensiling the average level of HCN was reduced by 62% (from 390 to 147 mg HCN/kg DM; Experiment 2). The HCN value was reduced by 93% after sun-drying in Experiment 3 (from 360 to 23 mg HCN/kg DM). Ensiled cassava leaves had an attractive smell and a pH of around 3.8, and appeared to be highly palatable.
3.2. Digestibility
Increasing the level of CLM and ECL in the diet led to increases in EE, NDF and CF, and to decreases in nitrogen free extracts (NFE) (Tables 1, 2 and 3). These changes re¯ect the higher concentration of fat-soluble pigments, NDF and CF in CLM and ECL compared with soybean meal.
In Experiment 1 feed refusals were noted on the diet in which all of the CP came from CLM, and to a lesser extent on the diet with 0.70 replacement. Digestibility coef®cients of all nutrients were highest (P<0.001)for the basal diet with linear decreases as CLM levels were increased (Table 5). The degree of depression was much more marked for CP and EE than for the other nutrients in the diet. The apparent digestibility of OM and all nutrients in Experiments 2 and 3 decreased linearly (P<0.001) as the proportion of ECL
Table 4
Nutrient (g/kg DM) and HCN content (mg/kg DM) of some varieties of cassava leaves grown in south Viet Nam Variety Crude
India 310 141 117 317 78 411 58
Gon 285 135 146 355 79 285 17
Japan 271 146 101 421 61 347 57
KM60 254 144 97 455 50 490 23
KM95 239 156 107 439 59 360 20
(Experiment 2) and CLM (Experiment 3) in the diet increased from 0 to 0.45 of the crude protein replaced (Table 5).
The digestibility of nutrients in CLM and ECL can be estimated from regression equations of the effect of CLM and ECL inclusion on nutrient digestibility of the diets (Table 6). The digestibilities of all nutrients in CLM and ECL were signi®cantly lower compared with the basal cassava root meal diet.
Table 5
Regression equations of apparent nutrient digestibility of cassava root meal based diets with inclusion of protein from cassava leaf meal (CLM) and ensiled cassava leaves (ECL) in Experiments 1, 2 and 3a
Intercept SD Slope SDb R2
Experiment 1
dOM 0.94 0.005 ÿ0.0021 0.008 0.93
dCP 0.83 0.017 ÿ0.0039 0.027 0.94
dCF 0.74 0.037 ÿ0.0025 0.058 0.84
dNFE 0.97 0.004 ÿ0.0007 0.005 0.92
dEE 0.68 0.029 ÿ0.0039 0.046 0.89
Experiment 2
dOM 0.95 0.009 ÿ0.0017 0.031 0.94
dCP 0.89 0.014 ÿ0.0042 0.051 0.97
dCF 0.79 0.019 ÿ0.0038 0.066 0.94
dNFE 0.98 0.002 ÿ0.0006 0.009 0.93
dEE 0.72 0.026 ÿ0.0042 0.093 0.91
Experiment 3
dOM 0.96 0.003 ÿ0.0019 0.010 0.95
dCP 0.87 0.028 ÿ0.0053 0.100 0.93
dCF 0.75 0.020 ÿ0.0047 0.072 0.94
dNFE 0.98 0.005 ÿ0.0007 0.017 0.87
dEE 0.71 0.033 ÿ0.0049 0.119 0.89
adOM: digestibility of organic matter; dCP: digestibility of crude protein; dCF: digestibility of crude ®bre;
dNFE: digestibility of N-free extract; dEE: digestibility of ether extract.
bSD10ÿ2.
Table 6
Estimated apparent digestibility of nutrients of cassava leavesa
Experiment 2 Experiment 3
ECL SDb CLM SDb
dOM 0.52 0.04 0.49 0.04
dCP 0.51 0.07 0.51 0.20
dCF 0.59 0.06 0.44 0.50
dNFE 0.83 0.01 0.96 0.03
dEE 0.53 0.05 0.39 0.07
adOM: digestibility of organic matter; dCP: digestibility of crude protein; dCF: digestibility of crude ®bre;
dNFE: digestibility of N-free extract; dEE: digestibility of ether extract.
3.3. N utilization
The amount of N excreted in faeces increased (P<0.001) with the level of leaf meal in the diet (Table 7). On the basal diet faecal N excretion was lowest, while urinary N excretion was highest. There was a linear decrease (P<0.001) of N in urine with increasing inclusion of cassava leaf CP in the diets (Table 7). Nitrogen retention (g/day) and N utilization (N retained as proportion of N digested) were signi®cantly (P<0.001) depressed with increasing proportions of CP from cassava leaves in the diet (Table 7).
4. Discussion
CP contents of the six varieties of cassava leaves analysed in the present study were found to be very variable and rather high, which was in good agreement with earlier data (Moore, 1976; Yeoh and Chew, 1976). The protein content of cassava leaf depends on variety, stage of maturity, soil fertility and climate (Rogers and Milner, 1963; Eggum, 1970; Ravindran, 1990). The CF content varied from 97 to 146 g/kg, these values being in line with the results of Oke (1990). The proximate composition of cassava leaf meal was similar to that of dehydrated alfalfa meal (Ravindran, 1990).
The results reported here also con®rm that the HCN content shows large variations, which agrees with other reports (Chew, 1972; Yeoh and Oh, 1979; Ravindran and Ravindran, 1988). It has been shown in previous studies that cassava leaf meal with low concentrations of HCN can be produced by sun-drying or ensiling (Gomez and Valdivieso, 1984; Ravindran, 1993). In our study, after 2 days of simple sun-drying alone,
Table 7
Regression equations of N in faeces (g/day), urine (g/day), nitrogen retention (g/day) and N utilisation (proportion of N digested) in cassava root meal based diets with inclusion of cassava leaf meal (CLM) and ensiled cassava leaves (ECL) in Experiments 1, 2 and 3
Intercept SD Slope SD R2
Experiment 1
N faeces 4.7 1.07 0.09 0.02 0.93
N urine 9.7 0.53 ÿ0.04 0.01 0.90
N retention 13.8 0.89 ÿ0.09 0.01 0.95 N utilisation 0.60 0.05 ÿ0.16a 0.08a 0.78
Experiment 2
N faeces 2.5 0.22 0.09 0.01 0.95
N urine 9.2 0.20 ÿ0.02 0.01 0.84
N retention 12.9 0.40 ÿ0.09 0.02 0.90 N utilisation 0.58 0.02 ÿ0.13a 0.06a 0.79
Experiment 3
N faeces 4.1 0.70 0.16 0.02 0.95
N urine 12.3 0.08 ÿ0.05 0.01 0.92
N retention 14.8 1.41 ÿ0.11 0.05 0.80 N utilisation 0.55 0.02 ÿ0.14a 0.08a 0.68
around 90% of the initial HCN content was eliminated. This ®nding is supported by studies on the effect of temperature on HCN content (Ravindran, 1993; Bala Nambisan, 1994), which showed that when combining sun-drying with chopping and wilting, the action of endogenous linamarase on cyanogenic glucosides reduced HCN in the dried meal to levels which are safe for monogastric animals (Ravindran, 1993). It has been reported that free tannin contents of cassava leaves are also lowered considerably during drying (Padmaja, 1989).
However, our results also showed that the reduction of HCN was only 62% in the case of ensiled cassava leaf. Linamarase, which hydrolyses cyanogenic glycosides, is very active at a pH range of 5±6, but no hydrolysis of the HCN takes place at pH values of 2±4 (Oke, 1994). This could explain why sun-drying was more effective in removing HCN than ensiling in the present study.
Other studies on cassava root chip silage and cassava waste silage also show that HCN levels were reduced to between 25 and 36% of the initial total HCN concentration of the corresponding cassava waste residue (Gomez and Valdivieso, 1984; Nguyen Thi Loc, 1996). However, the present results are in contrast to the ®ndings of a study where ensiling cassava leaves reduced HCN concentrations more than by sun-drying (Bui Van Chinh, 1990). In agreement with previous reports the present study shows that with proper processing techniques it should be possible to produce cassava leaf meal with low levels of HCN.
The present study shows that increasing the level of inclusion of cassava leaves in a cassava root meal based diet for growing pigs resulted in a linear decrease in the total tract digestibility of OM and CP, in accordance with earlier studies on ®brous feed ingredients (Kornegay, 1978; Kennelly and Aherne, 1980). In agreement with the present study, Sarwat et al. (1988) reported a linear decrease in the total tract apparent digestibility of OM when pigs were fed diets with inclusion of 0, 0.15 and 0.30 of the protein from cassava leaf meal. However, the digestibility coef®cients in our study were higher, which was most likely due to the use of different basal diets in the two studies, as it has been demonstrated that the digestibility of cassava root meal based diets for pigs is better than that of cereal-based diets (Gomez and Valdivieso, 1984; Patridge, 1985).
In the present study the OM digestibility coef®cients of the diets were reduced by 0.026 and 0.037 units per 10 g increase of CF content in the diet from ECL and CLM, respectively, and by 0.016 and 0.022 units per 10 g increase of NDF content in the diet from ECL and CLM, respectively. The magnitude of the depression caused by increasing the CF content originating from ECL was comparable with the results of Just (1982a, b) from cereal-based diets fed to growing pigs and with ®bre from cereal grains (ÿ0.029) and cereal straw (ÿ0.021), respectively. However, the depression in digestibility was considerably higher than in the study of Lindberg and Andersson (1998), who reported a decrease in OM digestibility of 0.010 units per 10 g increase of CF content in the diet and 0.008 units per 10 g increase of NDF content in the diet when temperate forage meals were included in a barley-based diet fed to growing pigs.
Dierick et al., 1989). These effects are variable depending on a number of factors such as the plant source (degree of ligni®cation), the level of ®bre and the feeding level (Oke, 1978; Ravindran and Ravindran, 1988; Dierick et al., 1989; Ravindran, 1990). In addition a higher ®bre content will increase the rate of passage of food through the alimentary tract (Gargallo and Zimmerman, 1981), which will increase the excretion of metabolic (Whiting and Bezeau, 1957) and bacterial N, the latter due to a more extensive fermentation in the hindgut (Mason and Palmer, 1973).
Tannins present in cassava leaves may be another factor that could contribute to the low protein digestibility and which could also result in a poor amino acid availability (Kumar and Singh, 1984). Tannins were not analysed in the present study. However, reported values for tannins in cassava leaves are 30±50 g/kg and would normally have little effect on digestibility (Ravindran, 1990).
Despite the same N intake on the control diet and the diets with cassava leaf inclusion, urinary N losses on the CLM and ECL diets were reduced and N excretion in the faeces was increased. This indicated that the utilization of the dietary N was changed, resulting in a shift of N excretion from the urine to the faeces. The gradual reduction in urinary N excretion was in accordance with the measured decrease in CP digestibility with cassava leaf inclusion. In the present study, the N utilization deteriorated with increasing inclusion of cassava leaf protein in the diet, despite a favourable essential amino acid composition compared with soybean meal (Table 8) and in contrast to earlier ®ndings in growing pigs, where a shift in N excretion from urine to faeces was without any major effect on N balance (Mason et al., 1976; Just, 1982a, b; Dierick et al., 1983). The most likely explanation for the results in the present study was a low digestibility of cassava protein. In addition, cassava leaf protein is de®cient in the sulphur-containing amino acids (SAA) (Eggum, 1970; Yeoh and Chew, 1976), and the SAA are used in the detoxi®cation of HCN (Oke, 1978; Ravindran, 1993). This could further have imposed limitations on the ef®ciency of amino acid utilization from cassava leaves in the present study. It has been demonstrated that supplementation with methionine can markedly improve the protein value of cassava leaf protein (Olson et al., 1969; Eggum, 1970; Lee and
Table 8
Amino acid composition of cassava leaves and soybean meal (g/16g N)
Amino acid Cassava leaves Soybean meal
(1)a (2)b (1) (2)
Threonine 4.40 4.30 2.78 3.20
Valine 5.60 5.90 3.33 7.30
Methionine 1.90 7.20c 1.40 6.60c
Isoleucine 4.50 5.30 3.52 4.50
Leucine 8.20 9.30 6.22 7.90
Phenylalanine 5.40 6.70d 4.11 5.20d
Lysine 5.90 6.80 3.76 6.50
Hutagalung, 1972). However, it is questionable whether supplementation would be economically feasible in developing countries.
The adverse effects on intake noted by other authors were assumed to be due to the high HCN levels in fresh leaves (Mahendranathan, 1971; Lee and Hutagalung, 1972). Also in the present study intake was found to be a problem when the level of leaf meal rose to 400 g/kg dietary DM, and some negative effects were found at inclusion levels of around 300 g/kg.
There were no indications of cyanide toxicity on any of the diets in the present study, for both sun-dried and ensiled cassava leaves. This is in agreement with the ®nding of Twe (1991), who concluded that drying and ensiling are effective ways of reducing the toxicity of cassava products. The recommended safety level of HCN in the diet is below 50 mg HCN/kg (Bolhuis, 1954), a level which was not reached in any of the diets in the present study.
5. Conclusions
The available data indicate that cassava leaf meal has a potential as a feed for pigs in the tropics. It represents an unconventional feed resource that could be developed into a feed with all the impact of alfalfa meal in temperate countries. However, the use of proper processing techniques is essential. Ensiling is as good a method as sun-drying for preservation of cassava leaf, and it would appear to be the more attractive method of processing when the harvest coincides with the wet season, but is likely to be restricted to an on-farm operation due to the high volume and short shelf-life of the ensiled product. From a practical and economic point of view, sun-drying would be the method of choice in the developing countries of the tropics.
Acknowledgements
The ®nancial support of the Swedish Agency for Research Co-operation with Developing Countries (SAREC) is gratefully acknowledged.
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