Workshop-seminar, 23-25 May, 2005, MEKARN-CTU

Making Better Use of Local Feed Resources

060104ba

Evaluation of the economical efficiency of using cassava leaves (variety KM 94) in diets for pigs in Central Vietnam

Nguyen Thi Hoa Ly and Le Duc Ngoan

Hue university of Agriculture and Forestry, Vietnam
lydohoai@dng.vnn.vn

Abstract

In Vietnam, cassava has rapidly changed its role from a food crop to an industrial crop. New high-yielding cassava varieties, such as KM60, KM94 and KM98, and more sustainable production practices, have increased the economic effectiveness of cassava production, especially in the Central region. Cassava leaves of the KM94 variety are high in protein (28 % CP as DM) and thus have good potential as a protein source for animals. The greatest limitation to the use of KM94 cassava leaves as animal feed is the very high HCN content (1745 mg/kg DM) of the fresh leaves. These studies therefore focus on the influence of preservation method on the HCN content of KM94 cassava leaves and an evaluation of the economic efficiency of feeding the ensiled cassava leaves to growing pigs.

The HCN content of fresh cassava leaves (KM94) was 1745 mg/kg DM and this decreased by 51 % after 24 h wilting by spreading on the floor. Various additives were compared in the ensiling process, and it was found that the inclusion of rice bran or cassava root meal at levels of 5 or 10 % produced good quality silage that could be stored for at least five months. The HCN content of the ensiled leaves decreased very quickly during the first 30 days, and the content was only from 10.4 - 13.2 % of the initial level at 90 days after ensiling.

In diets for growing pigs, the inclusion of 10 % (as DM) ensiled KM94 cassava leaves as replacement for sweet potato vines did not affect the animals' health or overall performance, and resulted in a 10.4 % reduction in feed costs.

Keywords: Ensiled cassava leaves, KM94 variety; crude protein, hydrogen cyanid, live weight gain, daily feed intake, feed conversion ratio, growing pigs

Introduction

Cassava is an important carbohydrate source for millions of people in the tropics. In Vietnam, its roots and leaves are used as human food, animal feed and industrial raw material. At present, cassava has rapidly changed its role from a food crop to an industrial crop. New high yielding varieties were grown on more than 94.5 thousand ha in 2002 (Pham Van Bien et al 2003), and varieties, such as KM60, KM94 and KM98, and more sustainable production practices have increased the economic effectiveness of cassava production, especially in the Central region. In 2003, in Thua Thien Hue province KM 94 was grown on 1708 ha, and the root yield obtained was between 22.8 and 23.9 tonnes/ha (Phuoc 2004). A new cassava processing factory was built in Hue City for producing starch, and the province will increase the area planted with this variety up to 4000 ha in 2005.

At root harvest time, yield of fresh foliage of KM94 is about 5 to 9 tonnes/ha (Hy 2004) and leaf yield 5 to 7 tons/ha (Hoa Ly 2004 unpublished data). Cassava leaves of the KM 94 variety have a high crude protein concentration (25.0 to 34.7 % CP in DM) (Bui Huy Nhu Phuc et al 2001; La Van Kinh 2003; Hoa Ly 2004), and thus has good potential as a protein source for animal feeding.

Because of the presence of the cyanogenic glucosides, linamarin and lotaustralin, in cassava and their hydrolysis by the endogenous enzyme linamarase to cyanohydrins, which break down to hydrogen cyanide (HCN), cassava consumption is often linked with cyanide toxicity (Bala Nambisan 1994). The most common procedures for reducing the cyanide content are sun-drying and ensiling (Duong Thanh Liem et al 2000; Nguyen Thi Hoa Ly et al 1999, 2000, 2001; Nguyen Thi Loc et al, 2001; Bui Huy Nhu Phuc et al 2001; Wanapat 2001; Man and Wiktorsson 2001, 2005; Ly and Rodriguez 2001; Khieu Borin et al 2005). In the rainy season it is difficult to sun-dry, and so making silage is the most appropriate method to preserve cassava roots and leaves and reduce the toxicity of HCN. Fresh cassava leaves of the KM 94 variety have a very high HCN content (1745 mg/kg DM), so it is necessary to find appropriate methods to process and use KM 94 for animal feeding.

Objectives of the study

To find appropriate preservation and processing methods for cassava leaves of the KM94 variety.
To evaluate the economic efficiency of using ensiled KM94cassava leaves for pig feeding under on-farm conditions in Central Vietnam.

Material and methods

Experiment 1. On station evaluation of the effect of time of wilting and additives on the quality of cassava leaf (KM94) silage

Processing method of KM94 cassava leaves

The fresh leaves of cassava KM 94 were collected at time of root harvest and spread out on the floor for wilting. The fresh leaves, and at 12 hours and 24 hours after wilting, were analysed for DM, CP and HCN content. The leaves of cassava KM 94 after 24 hours wilting were separated from the stems and petioles, chopped into small pieces (2 - 3 cm), mixed with 0.5 % salt and additives (rice bran or cassava root meal at 5 or 10% levels) and sealed in plastic bags. The treatments were:

5 % CRM: Cassava leaves (KM 94) + 0.5 % NaCl + 5 % Cassava root meal
10 % CRM: Cassava leaves (KM 94) + 0.5 % NaCl + 10 % Cassava root meal

5% RB: Cassava leaves KM 94 + 0.5 % NaCl + 5 % Rice bran
10 % RB: Cassava leaves (KM 94) + 0.5 % NaCl + 10 % Rice bran

Silage samples were taken after 0, 30, 60 and 90 days of ensiling and analyzed for dry matter (DM), crude protein (CP) and HCN (AOAC 1984).

Experiment 2. Evaluation of the economical efficiency of using cassava leaves (KM94) in diets for growing pigs in Central Vietnam

Animals, experimental design and feeding

An experiment was carried out in three households in Huong Van village, Hue province, from February to May 2004. The three families raised a total of 12 crossbred pigs (Mong cai x Large White) with initial live weights of around 24 kg. Each farmer kept 4 pigs allocated at random to two pens, with 2 pigs per pen. One pen on each farm was fed a Control diet (traditional diet) which contained: maize, rice bran, ensiled cassava root, fish meal and sweet potato vines, while the second group was fed the experimental diet (KM 94) containing 10 % ECL in DM, replacing sweet potato vines (Table1). The diets were formulated according to the two growing phases, 20-50 kg (Phase 1) and 50-90 kg (Phase 2). The diets were fed according to a restricted allowance recommended by the National Institute of Animal Husbandry, Vietnam (NIAH 2001). The experiment lasted 60 days. The diets were distributed equally into 3 meals per day. Refusals were collected the following morning before the first meal. Drinking water was available ad libitum. The chemical composition of the feed ingredients is shown in Table 2.

The basal diet was compounded to have (in DM) 3066 kcal ME, 14.8 % CP, 0.65 % lysine and 0.29 % methionine (Phase 1), and 3042 kcal ME, 12.8 % CP, 0.58 % lysine and 0.25 % methionine (Phase 2). Protein in the experimental diet came from fishmeal and 10% ensiled cassava leaves (K 94) (Table 3).

Chemical analyses

The feedstuffs in the experimental diets were analyzed for dry matter (DM), crude protein (CP), crude fibre (CF) and HCN (AOAC 1984). Feed consumption was determined by weighing the amounts given and subtracting any feed remaining the following morning. The pigs were individually weighed initially, monthly and at slaughter, and daily weight gain, daily feed intake, feed conversion ratio and feed cost/kg live weigh gain calculated for each treatment.

Statistical analysis

The data collected were analyzed by the General Linear Model (GLM) procedure in the ANOVA program of Minitab version 13. Sources of variaton were treatments and error.

Table 1. Design of experiment
Parameter	Control	KM94
Number of pigs	6	6
Days of experiment	60	60
Initial LW (kg)	24.0	24.5
Diet	Basal diet	Basal diet
Sweet potato vines (% of basal diet DM)	10	-
Ensiled KM 94 leaves (% of basal diet DM)	-	10

Table 2. Chemical composition of the feed ingredients (on DM basis except for DM which is on fresh basis)
Ingredient	DM (%)	*ME^ (Kcal)**	CP (%)	CF (%)	*Met(g/kg)**	*Lys(g/kg)**	HCN (mg/kg)
Maize	85	3140	8.4	2.4	1.7	2.74	-
Rice bran	86	2500	9.9	13.5	2	4.2	-
ECR**	42	1200	1.3	1.61	0.17	0.45	28.3
Fishmeal	88	3060	50.2	-	9.25	29.5	-
Sweet potato vines	13.4	300	2.4	2.4	0.52	0.95	-
Ensiled KM94**	42.2	882	8.1	4.5	1.25	3.54	75.4
* Calculated
** Analysed at 60 days after ensiling

Table 3. Ingredient content and chemical composition of the experimental diets (% DM basis)
Ingredient	Phase 1 ( 20 -50 kg)		Phase 2 ( 50 - 90 kg)
Ingredient	Control	KM94	Control	KM94
Maize	40	40	42	42
Rice bran	20	20	20	20
ECR	20	20	22	10
Fishmeal	10	10	6	6
Sweet potato vines	10	-	10	-
Ensiled KM94	-	10	-	10
*Composition, (% in DM)*
ME (KCal/kg DM)	3066	3050	3042	3046
CP (%)	14.8	15.0	12.8	12.9
CF (%)	9.4	8.7	9.3	9.1
Met (g/kg DM)	2.86	2.77	2.48	2.04
Lys (g/kg DM)	6.5	7.03	5.53	5.80
HCN (mg/kg DM)	13.8	31.7	15.2	33

Results and discussion

Experiment 1. On station evaluation of the effect of wilting time and additives on the quality of cassava leaf ( KM94) silage

The DM of the fresh cassava (KM94) leaves increased significantly after wilting for 12 hours or 24 hours. The aim in wilting is to reduce the moisture and HCN content in cassava leaves. Pre-wilting is a very important step to reduce moisture content of fermenting material, and several researchers have reported that a DM content of material of from 35 to 40 % is suitable for ensiling (Liu Jian Ping and Zhuang Zhong Tang 2000). After wilting for 24 hours, the DM % of the cassava leaves was 37.8 %, which is suitable for ensiling. Higher levels of moisture will cause the sugar and colloidal matter in plant liquid to be diluted, which will damage the lactic acid bacteria and may cause the silage to be putrid.

Table 4: Effect of time wilting on the DM, CP and HCN concentration of cassava leaves KM94
	DM (%)	CP (% DM)	HCN (mg/kg fresh )	HCN (mg/kg DM)
Fresh Leaves of KM94	27.86^a	28.26	486.^a	1745^a
Wilting after 12 h	32.56^b	27.31	428^b	1313^b
Wilting after 24 h	37.82^c	27.04	335^c	885^c
SE	0.274	0.403	6.29	19.5
P	0.000	0.16	0.001	0.001
a,b,c Mean values within columns without a common letter are different at p<0.05

The HCN content of the cassava leaves decreased after wilting (Table 4). The HCN content of the fresh cassava leaves was 1745 mg/kg DM, that was reduced to 1313 mg and 885 mg/kg DM after wilting for 12 and 24 hours, respectively. The HCN content thus was only about 75 -51 % of the initial level after 12 and 24 hours wilting, respectively.

Cassava leaves are often wilted at ambient temperatures of around 30 ⁰C. Bala Nambisan (1994) observed that wilting for a period of 12 hours causes further reduction in total cyanogens to 24 % of the initial level. Padmaja (1989) also observed that wilting whole branches under shade followed by drying detached leaves at 60⁰C was better than chopping wilted leaves and drying at 60⁰C. Drying of chopped leaves at 70⁰C results in 70 % retention of cyanogens. Wilting fresh leaves is effective in removing cyanogens, and the longer the wilting time, the lower the retention of cyanogens.

Table 5. Effect of additives and ensiling time on the pHof cassava leaf (KM94) silage
	Ensiling time, days
	0	30	60	90
KM 94 + 5 % CRM	6.38	5.15	5.04	4.67
KM 94 + 10 % CRM	6.42	4.24	5.21	4.49
KM 94 + 5 % RB	6.25	5.32	5.17	4.47
KM 94 + 10 % RB	6.23	4.87	4.86	4.47

Changes in pH with time confirmed the visual observations that all treatments resulted in silage of acceptable quality. pH values fell within 30 days to between 4.24 and 5.15 and fell further to 4.47 - 4.67 for all treatments after 90 days ensiling (Table 5)

Table 6. Effect of additives and ensiling time on the DM content of cassava leaf (KM94) silage
Additive	Ensiling time, days				SE	P
Additive	0	30	60	90	SE	P
KM 94 + 5 % CRM	40.5	40.9	40.3	38.1	0.680	0.068
KM 94 + 10 % CRM	43.0	43.1	41.8	42.2	0.586	0.404
KM 94 + 5 % R.bran	40.2^a	41.9^b	40.2^a	38.5^c	0.285	0.000
KM 94 + 10 % R.bran	42.6^a	43.9^a	41.1^b	39.6^b	0.638	0.007
Average	41.6^a	42.4^b	40.9^b	39.6^b	0.437	0.000
a,b,c: Mean values within rows without a common letter are different at P<0.05

Table 7. Effect of additives and ensiling time on the CP (% in DM) of cassava leaf (KM94) silage
Additive	Time of ensiling, days				SE	P
Additive	0	30	60	90	SE	P
KM 94 + 5 % CRM	24.39^a	23.11^b	22.58^b	20.86^c	0.176	0.000
KM 94 + 10 % CRM	24.34^a	21.95^b	21.41^b	19.04^c	0.204	0.000
KM 94 + 5 % R.bran	24.84^a	23.26^b	22.79^b	21.88^c	0.134	0.000
KM 94 + 10 % R.bran	25.34^a	23.81^b	23.41^b	22.56^c	0.049	0.000
Average	24.73^a	23.03^b	22.55^b	21.08^b	0.265	0.000
a,b,c: Mean values within rows without a common letter are different at P<0.05

Both additives at 5 or 10 % inclusion resulted in a good quality silage (Table 6). The DM content of the silage decreased slightly from 0 to 90 days of ensiling. Significant losses of DM were as a result of the activity of plant enzymes on the water-soluble carbohydrates, resulting in carbon dioxide and water. Most losses of nutrients occur as a result of aerobic deterioration before the material is ensiled, or as result of ingress of air during storage or after opening the silo.

The crude protein content (Table 7) with all additives decreased significantly from 0 to 30 days of ensiling, and then decreased slightly from 30 days until 90 days ensiling. Concentration of crude protein in the KM94 silage fell for all treatments by 3-5 % , probably as a result of bacterial degradation . Plant enzymes also bring about proteolysis and the production of amino acids and peptides from the protein of the original material.

Table 8. Effect of additives and ensiling time on the HCN (mg/kg DM) content of cassava leaf silage
Additive	Time of ensiling, days				SE	P
Additive	0	30	60	90	SE	P
KM 94 + 5 % CRM	773^a	649^b	363^c	231^d	22	0.001
KM 94 + 10 % CRM	706^a	638^a	311^b	181^c	17	0.001
KM 94 + 5 % R.bran	767^a	594^b	324^c	190^d	19	0.001
KM 94 + 10 % R.bran	705^a	574^b	293^c	190^d	18	0.001
Average	738	616	323	198
a,b,c: Mean values within rows without a common letter are different at P<0.05

The HCN content of the ensiled cassava leaves decreased very quickly from 0 days (after leaf wilting 24 hours) to 30 days and then further decreased until 90 days after ensiling (Table 8). The HCN content of the fresh cassava leaves was 1745 mg/kg DM, and was reduced to 885 mg/kg DM after 24 hours of wilting, when the HCN content was only about 51 % of the initial level. Then at 90 days after ensiling, the HCN content of the cassava leaves had fallen to 181- 231 mg/kg DM, only about 10.4 - 13.2 % of the initial level. Many previous studies concluded that ensiling is a convenient way of preserving the nutritional value and reducing the toxicity of fresh cassava leaves (Hoa Ly 1999; 2000, 2002; Loc 1996, 2001; Phuc et al 2001; Ly and Rodriguez 2001; Man and Wiktorsson 2001, 2005; Khieu Borin et al 2005).

Our previous research, on using various additives in the ensiling process, showed that the inclusion of rice bran or cassava root meal at levels 5 or 10 % and fresh cassava roots at levels of up to 50 % (on fresh basis of local variety cassava leaves) produces good quality silage that can be stored for at least five months. The HCN content of the ensiled local variety cassava leaves decreased very quickly during the first 30 days, and the HCN content was only about 20 - 28 % of the initial level at 90 days after ensiling.

Thus, cassava leaves (KM94) after wilting 24 h then ensiling, could be a suitable alternative way of preserving when the harvest of cassava coincides with the rainy season. The technique is simple, cheap and suitable for farm conditions in Central Vietnam.

Experiment 2. Evaluation of the performance and economic efficiency of using KM 94 cassava leaves for growing pigs in Central Vietnam

Final live weight, daily weight gain and feed conversion ratio

There were no differences between treatments for final weight, daily live weight gain and feed conversion ratio (Table 9).

Table 9. Effect of using ensiled cassava leaves KM 94 in diet on performance and efficiency economic of crossbred growing pigs
	Control diet	KM94 diet	SE	P
Initial LW (kg)	24.0	24.5	0.303	0.270
Final LW (kg)	59.4	61.1	2.168	0.599
Daily gain (g/day)	590	610	35	0.701
DM intake (kg/pig/day)	1.66	1.63	0.013	0.135
FCR (kg DM/kg LWG	2.82	2.78	0.171	0.830
Feed cost (VND/kg LWG)	7,285	6,525	407	0.216
Compared to control (%)	100	89.6

The fresh KM 94 cassava leaves had a high HCN content, but this was reduced by ensiling so that there was no effect on the performance of growing F1 pigs.

Conclusions

Wilting fresh cassava leaves (KM 94 variety) is effective in removing cyanogens; the longer the wilting time, the lower the retention of cyanogens.
Inclusion of rice bran or cassava root meal at levels of 5 or 10 % produces good quality silage that can be stored for at least five months. The HCN content of ensiled cassava leaves (KM94) decreased very quickly during the first 30 days, and the HCN content was only from 10.4 to 13.2 % of the initial level at 90 days after ensiling.
The inclusion of 10% (as DM) ensiled cassava leaves (KM94), as replacement for sweet potato vines in diets for growing pigs, did not affect the animals' health or overall performance.
KM 94 cassava leaves can be used as a protein supplement for feeding pigs, and will result in higher benefits for farmers in Central Vietnam.

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