Ensiled cassava leaves and duckweed as protein sources for fattening pigs on farms in Central Vietnam

Du Thanh Hang

College of Agriculture and Forestry, Hue University, Vietnam

Abstract

Forty-four crossbred pigs (mainly Large White x Mong Cai) about 3 months old and 23-25 kg initial weight were allocated  among  two groups of families (4 pigs/household) to compare effects of supplementing the traditional diet with either ensiled cassava leaves or fresh duckweed. In six farm households (trial 1) the comparisons (two pigs per treatment) were:  ensiled cassava root, brewery by-product (brewers' grains), rice bran and sweet potato vines (control) or the same as the control but with ensiled cassava leaves replacing the sweet potato vines. The cassava leaves were ensiled with 5 % molasses and stored 21 days before feeding. The cassava roots were ensiled with 0.5% common salt and stored 21 days before feeding. In five farm households (trial 2) the comparisons (two pigs per treatment) were the same as for the trial with ensiled cassava leaves except that fresh duckweed replaced the ensiled cassava leaves. The duckweed (Lemna minor) was grown in artificial ponds lined with polyethylene sheets on one farm and in natural ponds in the others.  The ponds were fertilized with manure from buffaloes and pigs.   The duckweed was harvested daily and fed immediately after harvesting.

In five out of six farms in the first trial, pigs fed ensiled cassava leaves grew faster than the controls receiving sweet potato tops, but the overall difference was not significant. On all five of the farms in the second trial, the pigs supplemented with fresh duckweed consumed more dry matter and grew 35% faster (P=0.001).  It is concluded that in pig fattening diets based on ensiled cassava root, rice bran and brewers' grains: ensiled cassava leaves can replace sweet potato vines with no effect on growth or carcass traits; and that fresh duckweed (providing 5% of the diet dry matter) has a stimulating effect on liveweight gain which may be partially explained by the additional intake of protein, although other factors are likely to be involved.

Key words; Pigs, fattening, on-farm, cassava, ensiled cassava leaves, duckweed

Introduction

In Central Vietnam, pig production plays an important role in the farming activities especially for small-holders. The pigs provide manure, meat and income. In recent years, the income from pig raising is very low and in some cases is negative because the pigs grow slowly and the costof feeds is expensive. The main cause is the imbalance in the nutrients in the ration  particularly the energy and protein ratio. The main energy sources are cassava, cassava-by products, rice bran, maize and sweet potato. Those feeds have a low protein content. The conventional protein sources such as fish meal, soya bean meal and groundnut cake are not used by the farmers because they are too expensive and the farmers do not have enough money to buy them. Thus there is a need to identify and promote other protein sources especially those that can be produced on the farm.

Many researchers have shown that the leaves from different plants can be used as protein sources in pig feeding at the small scale level of production. Bui Van Chinh et al (1993) showed that ensiled soya bean foliage can replace 20-37 % of the protein in the ration without affecting the performance of the pigs. According to Perez (1996), the fresh foliage from immature soya bean, planted at weekly intervals and harvested when the grain isat the milk stage, has considerable potential as a protein source in the tropics that can be available in the wet season, and even year round if irrigation is available.

According to Montaldo (1977), cassava  plants can withstand defoliation for several years if they receive adequate fertilization and irrigation, and under such management have the potential to produce up to 4 tonnes of protein per hectare, annually. Ensiling of cassava leaves is an appropriate way to conserve them (Limon 1992; Bui Van Chinh et al 1992; Du Thanh Hang 1998). It has been shown that the ensiled leaves can provide all the protein in a diet of sugar cane juice for native Mong Cai pigs (Du Thanh Hang et al 1997) and up to 50% of the protein in diets based on ensiled cassava roots (Du Thanh Hang 1998).

Another plant protein source with high potential is duckweed (Rodriguez and Preston 1996; Nguyen Duc Anh et al 1997; Le Ha Chau 1998). The protein is more digestible than in cassava leaves (Nguyen Van Lai and Rodriguez 1998) and with appropriate fertilization of the pond water the protein content can be as high as 35-40% in the dry matter (Leng et al 1995; Rodriguez and Preston 1996; Nguyen Duc Anh et al 1997; Le Ha Chau 1998). The balance of essential amino acids in duckweed is considered to be comparable to that in soya bean meal (Muztar et al 1976;  Rusoff et al 1980). As with ensiled cassava leaves, pigs have been fed with duckweed as the only source of supplementary protein in diets of: sugar cane juice (Du Thanh Hang et al 1997; Nguyen Van Lai and Rodriguez 1998); ensiled cassava roots (Nguyen Van Lai and Rodriguez 1998);  and mixtures of ensiled cassava roots and rice bran (Nguyen Van Lai 1998). Up to the present, most of the work with duckweed supplementation of pig diets has been done on-station. The trial of Nguyen Van Lai (1998) was done on-farm but with very young pigs (weight range 5 to 20 kg). There appear to be no reports on the use of duckweed with fattening pigs under farm conditions.

Objective

The aim of this study was to evaluate ensiled cassava leaves and duckweed as protein supplements in diets for growing-fattening pigs fed on local resources at small-holder farm level.

Materials and methods

Location

The study was done in Thuy Xuan village which is located in the upland area of Thua Thien Hue Province. The pig population in the area is estimated to be of the order of 5000.  The number of pigs per family is stratified according to income, as follows: high income farmer:12 - 15 pigs, middle income: 4 -6 pigs and poor farmer: 1 -2 pigs. The traditional feeds are dried cassava root, rice bran and brewery by-products. The crude protein in the dry matter of the typical diets was calculated to be less than 9 %.   Rice bran is the most expensive ingredient.  Cassava root is available in Thuy Xuan constantly. The area planted in cassava is about 65 ha, with a productivity of 3,500 kg/ha.  The population density is about 1 person/600 m² and there are 30 ha of springs, ponds and lakes. This means that there are opportunities for the farmers to grow water plants.

Choice of farmer

Feeding trials were carried out in farm households in Thuy Xuan village from May to November 1997. The families were selected on the basis of:

• The farmers' willingness to participate in the research
• Availability of a closed pig pen with cement floors of adequate size.
• Cassava and duckweed availability on the farm

Treatments and design

Trials were carried out with two groups of farmers.  In each farm, two pigs received the conventional diet; two more pigs were fed the experimental diet which was the conventional diet plus either fresh duckweed (group 1) or ensiled cassava leaves (group 2) in each case replacing fresh sweet potato vines. A total of 9 households took part in the trials.  In two households the trial was done with both ensiled cassava leaf and duckweed (with four pens each having 2 pigs).

Animals and feeding

Forty-four crossbred pigs (mainly Large White x Mong Cai) about 3 months old and 23-25 kg initial weight were allocated among  two groups of families (4 pigs/household); one group of  6 families and one of 5 families.The pigs were vaccinated against Pasteurella, Erysipelas and Hog cholera, dewormed and ear-notched. An adaptation period of 20 days was allowed before starting the experiment, which lasted for 120 days. The following diets were investigated:

Ensiled cassava (6 families)

• Control: This consisted of ensiled cassava root, brewery by-product (brewers' grains), rice bran and sweet potato vines.
• Ensiled cassava leaves: The same as the control but with ensiled cassava leaves replacing the sweet potato vines

The cassava leaves were ensiled with 5 % molasses as described by Du Thanh Hang (1998) and stored 21 days before feeding. The cassava roots were ensiled with 0.5% common salt (Nguyen Thi Loc et al 1996) and stored 21 days before feeding.

Duckweed (5 families)

The diets were the same as for the ensiled cassava leaves except that fresh duckweed replaced the ensiled cassava leaves. The duckweed (Lemna minor) was grown in artificial ponds lined with polyethylene sheets (area of 10m*2m) on one farm and in natural ponds in the others (average area per pond was about 50m²). Manure from buffaloes and pigs was applied to the ponds (about 5 kg buffalo manure weekly and 3 to 4 kg pig manure every second day). The duckweed was harvested daily and fed immediately after harvesting.

Procedure

The pigs were weighed in the early morning each month using a 100 kg capacity portable scale with an accuracy of 0.5 kg. Feeds offered and refused were recorded for each meal (3 times a day) using a 20 kg capacity portable scale. The farmers mixed all the ingredients prior to feeding which was done three times per day. Feed samples were taken (two times for cassava leaves and 4 times for duckweed)for analysis of dry matter, nitrogen and crude fibre using the procedures of AOAC (1985).  

Carcass measurements

At the end of the experiment, 6 pigs were slaughtered from each treatment and the carcasses were evaluated. Carcass weight was determined directly after slaughtering to calculate hot carcass dressing percentage. Carcass length was measured from the first rib to the pubis bone. Average back fat thickness and loin eye area were determined at the tenth rib. The carcasses were separated into lean meat, fat, bone and skin and the amounts recorded.

Statistical analysis

Mean values for effects of supplementation on weight gain, back-fat thickness and area of loin eye muscle were compared using the GLM option of the analysis of variance, determined with software of Minitab, release 10.2.  The sources of variation in the ANOVA was the source of supplement.  The analysis was made separately for each group of farmers.  

Results

Feed composition

The composition of the feed ingredients is shown in Table 1. The HCN levels in all the cassava products were below 100 mg/kg dry matter which is considered as the safe level to avoid toxicity (Tewe 1992). The protein content of the duckweed was almost twice that in the sweet potato vines; differences in the fibre content were less marked but favoured the duckweed.

Table 1: Composition of feeds
	Dry matter %	N*6.25 % in DM	Crude fibre % in DM	HCN mg/kg DM
Ensiled cassava leaves	35	27	15.3	70.7
Duckweed	6.48	30.1	8.3
Sweet potato vines	13.6	17.7	10.5
Rice bran	87.6	14.8	8.45
Cassava root meal	90	1.4	0.57	26.7
Brewers’ grains	21	25.3	12.7
Ensiled cassava root	40.2	1.5	0.92	65.3

The trial with ensiled cassava leaves

Feed intakes in the trial with ensiled cassava leaves are shown in Table 2. In the experimental diet the ensiled cassava leaves provided 9% of the diet dry matter (Figure 2) and 15.0% of the total protein (calculated from Table 2). The sweet potato vines were 9% of  the control diet dry matter (Figure 1) and  provided 13.4% of the protein (calculated from Table 2).

Table 2: Intakes of dry matter and of protein for pigs fed the conventional (control) diet or the control plus ensiled cassava leaves (ECL) replacing the sweet potato vines
Intake, g/animal /day (from day 0  to day 120)	Dry matter		Protein
	ECL	Control	ECL	Control
Ensiled cassava leaves	150	0	41
Sweet potato vines	0	190	0	34
Rice bran	910	820	134	110
Ensiled cassava root	620	620	9	5
Brewers' grains	340	340	86	29
Cassava root meal	50	50	0.0	0.0
Total DM	2,070	2,020
Total protein			270	250
Protein, % of DM			13.1	12.4

Figure 1: Ingredients in the control diet with sweet potato vines (% as dry matter)

Figure 2: Ingredients in the diet with ensiled cassava leaves (% as dry matter)

There were no differences in growth rate or feed conversion between the pigs fed the conventional diet and those receiving ensiled cassava leaves as replacement of the sweet potato vines. Feed costs were lower with ensiled cassava leaves supplementation.

Table 3: Mean values for growth rate and feed conversion in pigs fed the conventional (control) diet or the control with ensiled cassava leaves replacing the sweet potato vines
	ECL	Control	SE/Prob.
Liveweight, kg
Initial	25.8	23.3	0.89/0.16
Final	78.1	74.5	1.02/0.02
Daily gain	0.435	0.426	0.01/0.34
DM feed conversion	4.99	4.81	0.16/0.43
Feed cost/pig/day, VND	4,072	4,737	95/0.004
Feed cost/kg gain, VND	9,375	11,143	3.06/0.009

The trial with duckweed

The data on feed intake during the trial are shown in Table 4. The proportions of the diet contributed by the different ingredients are shown in Figures 3 and 4.

Table 4: Intakes of dry matter and of protein for pigs fed the conventional (control) diet or the control plus fresh duckweed (DW) replacing the sweet potato vines
	Dry matter		Protein
Intake, g/animal/day	DW	Control	DW	Control
Duckweed	100	0.00	30.1	0
Sweet potato vines	0.00	130	0	23
Rice bran	730	610	108	90.3
Ensiled cassava root	640	530	8.96	7.42
Brewers' grains	330	320	83.5	81.0
Cassava root meal	220	220	3.3	3.3
Total DM	2,020	1,810
Total protein			234	205
Protein, % in DM			11.6	11.3

Figure 3: Ingredients in the control diet with sweet potato vines (% as dry matter)

Figure 4: Ingredients in the diet with duckweed replacing sweet potato vines (% as dry matter)

The duckweed contributed 5% of the diet dry matter (Figure 4) and 12.9% of the total protein (Table 4) in the experimental diet. Comparable data for sweet potato vines in the control diet were 7% (Figure 3) and 11.2% (Table 4).  The total protein content in the dry matter was the same for both diets (11.6 and 11.3%).

Growth performance

Mean values for initial and final weight, weight gain and feed conversion are given in Table 5 for pigs fed the conventional diet (control) and the control diet with fresh duckweed replacing the sweet potato vines.  Pigs fed duckweed as a supplement were significantly heavier at the end of the trial (P=0.001), gained weight more rapidly (P=0.001) and had better feed conversion (P=0.001) than the control pigs fed sweet potato vines as the protein supplement.

Table 5: Mean values for growth rate and feed conversion in pigs fed the conventional (control) diet or the control with fresh duckweed replacing the sweet potato vines
	DW	Control	SE/Prob.
Liveweight, kg
Initial	20.3	19.0	1.33/0.50
Final	86.31	67.5	2.15/0.001
Daily gain	0.552	0.404	0.01/0.001
DM feed conversion	3.66	4.50	0.10/0.001

The data for growth rates on the individual farms show the consistency of the response to duckweed in the different locations (Figures 5). By contrast, in 5 out of the 6 farms in the trial with ensiled cassava leaf there was faster growth on this supplement compared with the control receiving sweet potato tops, but the overall effect was not significant.

Figure 5: Growth rates of pigs on individual farms fed the conventional diet (control) or with fresh duckweed replacing the sweet potato vines in the control diet

Figure 6: Growth rates of pigs on individual farms fed the conventional diet (control) or with ensiled cassava leaf replacing the sweet potato vines in the control diet

Carcass measurements

Mean values for carcass traits in a sample of pigs from both trials are shown in Table 6.

Table 6: Mean values for carcass traits for a sample of pigs from each trial
	Ensiled cassava leaves			Duckweed
	ECL	Control	SE	DW	Control	SE
Carcass yield, %	nd	nd		68.4	68.8	0.56
Carcass length, cm	88.3	80.7	3.12	85.0	80.0	0.85
Back fat, cm	3.1	3.03	0.53	3.2	3.0	0.10
Loin eye area, cm²	29.0	29.2	0.47	32.6	29.2	1.04
Composition of the carcass, %
Lean meat	40.6	40.3	0.55	42.1	41.3	0.66
Fat	34.7	34.9	1.0	33.8	33.9	0.38
Bone	14.9	15.9	0.52	15.0	15.9	0.68
Skin	9.73	8.86	0.33	9.1	8.87	0.08
nd: Not determined

There were no effects on carcass traits attributable to supplementation with either ensiled cassava leaves or duckweed (Table 6).

Discussion

The contrasting feature of the two trials was the highly significant improvement in growth rate and feed conversion when fresh duckweed replaced the sweet potato vines in the traditional diet and the less consistent and non significant effect when ensiled cassava leaves was the alternative supplement.  The origin of the pigs was the same and those on the control treatment performed similarly in both trials (404 g/day growth rate and 4.5 conversion in the duckweed trial and 426 and 4.81 in the trial with cassava leaf silage). The contribution to the diet of the protein from duckweed was less than that from ensiled cassava leaves (12.9 versus 15%) and although the former has a slightly better array of essential amino acids (compare the reports of Rusoff et al 1980 and Ravindran 1992) it is unlikely that this could be the sole explanation.  Working with scavenging native chickens in Cambodia, Hong Samnang (1998)  reported a significant improvement in growth rate when the birds had access to duckweed even though the amount consumed was small (contributing the equivalent of less than 1 g protein/day).  A stimulating effect of small amounts of duckweed (5% of the diet dry matter) in the diet of broiler chickens was also observed by Haustein et al (1994).

Conclusions

It is concluded that in pig fattening diets based on ensiled cassava root and brewers' grains:

• Ensiled cassava leaves can replace sweet potato vines with no effect on growth or carcass traits
• Fresh duckweed (average intake 1.5 kg/day) has a stimulating effect on liveweight gain (daily gain was increased by 37%) 

Acknowledgments

The author wishes to thank heradvisers, Dr. Thomas R. Preston and Lylian Rodriguez, for their help, encouragement and guidance; Mr Frands Dolberg for his interest in her studies and valuable advice; Le Duc Ngoan and Dr Nguyen Kim Duong for their  advice; Hoang Nghia Duyet,  Le Cong Son and Nguyen Quang Linh for their kind help and collaboration; Nguyen Van Ba, Nguyen Van Hung and leaders of the Thuy Xuan community for their help and collaboration.

A special thank to my husband, Le van Tuat, my son Le Minh Tuan and my daughter, Le thi Cam Tu, for their tender love, endless patience and support.

Financial support is acknowledged from the Danish Embassy in Hanoi, through a grant to theUniversity of Tropical Agriculture Foundation, and from SAREC organization in Sweden.   A preliminary version of this work was submitted as partial requirement for the Master of Science degree in Sustainable Use of Natural Renewable Resources of the UTA (1998).

References

Received 10 December 1998

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