| Livestock Research for Rural Development 9 (2) 1997 | Citation of this paper |
Nguyen Thi Loc, R Brian Ogle(1)and Thomas R Preston(2)
College of Agriculture, Hue University, Vietnam
An on-farm trial in Binh Dien and Xuan Loc villages in Central Vietnam compared
ensiling of cassava roots (ECR) (chipped by hand or ground by machine) with sun-dried
cassava root meal (CRM) with supplements of "A" molasses at levels from zero to
20%. The HCN content of the ground whole cassava root after ensiling for 60 days was
reduced from 109 ppm to 64 ppm, while ensiling the chipped root reduced HCN from 111 to 71
ppm. The optimum levels of "A" molasses replacing cassava root (ensiled or
dried) in pig diets with protein supply kept constant at 200 g/day was in the range of 15
to 20% for live weight gain and economic purposes. Mean live weight gains were 465
g/pig/day for the cassava root meal diet and 453 g/pig /day for the ensiled cassava root
diet each with 20% of "A" molasses. Feed costs/kg gain for the 20% molasses diet
with dried and ensiled cassava root were 11% and 27% less than for corresponding diets
without molasses.
There were 15 millions pigs in Vietnam in 1995 of which 95% are raised by small scale farmers. The energy and protein feed resources have a very high potential in Central Vietnam but there is a need to work out different methods to facilitate the management and to improve the knowledge about how to combine these resources in order to improve the nutritive value of the whole diet for pigs.
Cereal grains are needed for human consumption and cannot be spared for feeding pigs. Cassava and sugar cane on the other hand, have several advantages compared with other carbohydrate sources. Cassava and sugar cane are the main crops in the upland areas of Central Vietnam. The total production of fresh cassava root was 702,000 tonnes and of sugar cane 1.4 million tonnes in Central Vietnam in 1994 (Nguyen Sinh Cuc 1995). Approximately 60% of the sugar cane crop is processed by artisan methods in the villages giving rise to sugar-rich "A" molasses(3)
The total quantity of molasses resulting from the processing of the sugar cane has been
estimated at around 35,000 tonnes per year. The prices on a dry matter basis of both fresh
cassava root and "A" molasses are usually less than those of rice, maize and
cassava root meal (Nguyen Kim Duong and Le Duc Ngoan 1993).
The potential disadvantages of cassava roots are rapid perishability, their low protein
content and the presence of cyanide in all root tissues. However, through simple
processing, the disadvantage of perishability and cyanide can be overcome. The two most
widely used processing methods are sun-drying and ensiling. In the humid tropics,
especially in the wet season, sun drying is difficult and may result in the production of
a low quality product with severe Aspergillus and related aflatoxin contamination.
Artificial drying significantly increases the cost which makes the use of the root meal
non-competitive with cereal by products such as broken rice and bran. Ensiling of the
cassava root appears to be a more viable alternative.
On- farm feeding trials were conducted in two villages in Central Vietnam to evaluate
the effect of processing methods on pH and HCN content of ensiled cassava roots and the
effect of different levels of "A" molasses replacing cassava root meal or
ensiled cassava root on the performance of growing-finishing pigs.
Ensiled cassava root (ECR) was produced by washing and grinding (or chipping) the fresh
roots and adding salt (0.5% of the fresh weight of the root). The material was ensiled
immediately after processing, either in pits dug out of the ground, in a cement container
or in plastic bags. These were filled with ground or chipped cassava root as quickly as
possible and compacted properly to eliminate air, so as to minimise the loss of nutrients
by oxidation. Usually a polyethylene sheet was used to cover the ensiled material, to
create anaerobic conditions for fermentation. The time taken for preparation of the
cassava roots and the ensiling process was recorded.
Samples of the freshly processed root were taken on the day of ensiling and after 30,
60, 90, 120, 150 and 180 days for analysis of DM, hydrocyanic acid (HCN), organic acids
and pH. HCN was analysed by the method of Easley et al (1970). Organic acids (acetic,
lactic and butyric acids) were determined according to the method of Lepper et al (1982).
The families were selected in cooperation with the local Women's Union, and the criteria taken into consideration for selection were:
The experiment was carried out from May to November, 1995, in Binh Dien and Xuan Loc
villages. Pigs were purchased by groups of farmers with the assistance of the researcher
and the Women's Union of the villages. Seventy two crossbred (Mong Cai x Large White) pigs
of 18 kg initial weight were randomly assigned to 12 treatments with 3 replicates per
treatment and 18 farms (10 in Xuan Loc and 8 in Binh Dien). Each farm had 4 pigs fed the
same "A" molasses level, but 2 pigs per pen (1 castrate and 1 gilt) were fed
cassava root meal and 2 pigs were fed ensiled cassava root.
The design comprised 2 factors :
An adaptation period of 25 days was used to change to the experimental feed. The
experimental diets were given for 5 months. Diet composition and
amounts of dry matter supplied per pig per day are given in Tables 5 and 6. Feed samples
were taken for analysis of dry matter (DM), crude protein (CP), ether extract (EE), crude
fibre (CF) and ash, using AOAC procedures (AOAC 1985).
The methods of processing the cassava root were described earlier. The "A"
molasses was purchased from an artisan sugar factory in Binh Dien village. On the basis of
the results of Ospina et al (1995), the ad libitum feeding of the cassava root
was complemented by 200 g protein/day derived from a mixture of 75% groundnut cake and 25%
fish meal. The required weekly amounts of molasses (according to treatment) and cassava
root were weighed and put into plastic bags to facilitate the work of the farmers. The
farmers mixed these two ingredients immediately prior to feeding three times per day,
estimating the quantities needed at each feed according to indicated guidelines provided
by the researchers which were revised weekly. The protein supplement was also weighed in
weekly amounts and given in two feeds per day. The daily amount remained constant (384 g
groundnut cake: 120 g fish meal) throughout the experiment.
The pigs were weighed in the early morning every 30 days using a 100 kg capacity
portable scale with an accuracy of 0.5 kg. Records of feed consumption were kept by the
farmers and checked twice weekly during visits to the farms. All data collected were
analysed by analysis of variance using the General Linear Model ( GLM) procedure of
Minitab statistical software.
The ensiled whole cassava root had an acceptable aroma for pigs with no mould growth
and kept its white colour. After processing and before ensiling (Table 1) the HCN content
was highest in fresh thick peel (238ppm ) and lowest in fresh pulp (91 ppm). Tewe and
Iyayi (1989) analyzed Nigerian cassava and found that the HCN contents of fresh thick and
thin peel were much higher (364-815 ppm), while HCN in fresh pulp was only 34-301 ppm (
air dry basis). They considered that these differences of HCN were probably due mainly to
the variety and the time of harvest of the cassava. They further showed that the
concentration of HCN in the cassava root, when the thin peel was removed, was reduced by
only 5 % and there was a 3% reduction in content of energy and farmers spent 256 % more
time on peeling compared with no peeling.
The data (Table 2) indicate that the effect of both processing methods (grinding or chipping) was to increase the dry matter content, with increased length of the ensiling period from 0 to 30 days and 60 days, although this difference disappeared at 180 days. The increase of DM content in ground ensiled cassava root was higher than in chipped ensiled cassava root from 0 day to 30 days. Almost certainly the grinding (by machine) exposed a greater surface area to the air which facilitated loss of moisture. Chipping was by hand and thus the particles were larger and less likely to lose moisture. The ensiled material had some 10% more dry matter (after 150-180 days of ensiling) than the freshly processed root. A similar effect was reported by workers at CIAT (1978), who found that the dry matter content increased from 35 to 39% during the space of 25 weeks of ensiling.
The pH was reduced to about the same level (pH=4.0) for both processing methods after
30 days, and then decreased slightly to 3.7 at 90 days and remained at this value.
Effects of processing methods on cyanide content are shown in table 3. The HCN content
was affected by the processing method and was lower at all stages of ensiling in the
ground root than in the chipped root ( P=0.001). HCN levels for both processing methods
decreased very quickly up to 30 days and then continued to decrease more slowly up to 180
days. Ensiling ground cassava reduced HCN content to 70, 59 and 51 % of the initial value
after ensiling periods of 30, 60 and 180 days respectively, while ensiling cassava chips
reduced the HCN content to 80.6 and 54% of the initial value, respectively.
Similar findings were reported by CIAT (1981) and Gomez and Valdivieso (1988). These
results show that ensiling ground cassava was slightly better in reducing HCN. The
reported levels of reduction of cyanide content are sufficient to make the ensiled cassava
safe as a feed for pigs accordng to Gomez and Valdivieso (1988) who fed roots ensiled for
60 days with a residual cyanide content of 56ppm. Bolhuis (1954) proposed that the
toxicity of cassava cultivars could be rated as follows:
(*) Innocuous: less than 50 ppm HCN in fresh peeled tuber.
(**) Moderately toxic: 50-100 ppm HCN in fresh peeled tuber
(***) Dangerously toxic: more than 100 ppm HCN in fresh peeled tuber.
However, Ikediobi et al (1980) have reported that cassava containing 144 to 164 ppm HCN
after processing can be used for livestock in Nigeria.
The HCN level of ground ensiled cassava root after 60 days ensiling (64 ppm HCN) apparently caused no ill effect in the pigs used in the experiments on farm and on station.
The effect of the ensiling time on organic acid levels in the fresh cassava root is
shown in Table 4. The content of acetic and butyric acids decreased with increased
ensiling time, while that of lactic acid increased. The results are fairly similar to
those reported by Serres and Tillon (1972) who recorded levels of acetic and butyric acids
in ensiled cassava after three months of 0.3% and 0.09%, respectively.
Ensiled or dried cassava root with molasses on pig performance
The composition and chemical analysis of the feeds are shown in Tables 5 and 6. The
pigs on all dietary treatments readily consumed the diets with no palatability problems or
digestive upsets, except for a few cases of diarrhoea. Cassava diets have often been found
to be of low palatability due to the powdery nature of the root flour (Balagopalan et al
1988).
Overall treatment effects are shown in Table 7. The major parameters of biological
performance in finishing pigs (rate of gain and feed conversion) were significantly better
for dried cassava root meal than for the ensiled root, although the absolute differences
were relatively small (2.5 and 2.6%, respectively, for gain and feed conversion). The
relationship between molasses levels and live weight gains in pigs fed ensiled or dried
cassava root meal is shown in Figure 1. Live weight gains of pigs fed ensiled cassava
roots were lower than of pigs fed cassava root meal for "A" molasses levels from
0 to 15%. Live weight gains of pigs fed ensiled cassava roots were similar to those of
pigs fed cassava root meal for "A" molasses levels from 15 to 25%.
The response to "A" molasses appeared to be curvilinear with optimum
performance in terms of growth and feed conversion being observed for levels of between 15
and 20% of "A" molasses for both methods of processing the cassava root. These
results agree with those of Vinas and Cisneros (1990) who found that mean daily gains of
pigs were significantly greater for a group given 15-20 % molasses than for the controls.
In addition, the taste and consistency of the ration can be maintained by the addition of
molasses (Gomez 1979). The average growth rates of the experimental pigs were quite
satisfactory considering the genotype (exotic*local) and the restricted protein level (200
g/day). Average daily gains of pigs in Binh Dien village (436g/day) did not differ
(P=0.62) from those on farms in Xuan Loc (433 g/day) and there were no interactions
between village and the dietary treatments (P>0.70). This is evidence for the
reliability of data from on-farm experiments of the kind described in this study.
In contrast to the results for growth and conversion, feed costs per unit live weight gain were much lower (by 20%) for ensiled cassava root than for the sun-dried meal (Table 7) and followed a similar pattern as growth performance for the effect of molasses level, with the lowest feed costs corresponding to molasses levels of 15 to 20%.
The authors gratefully acknowledge the help of the People's Committee and the Women's
Union of Binh Dien and Xuan Loc villages, and the Women Union of Thua Thien Hue Province
in developing the activities with the farmers at the research sites. Thanks are due to the
Swedish International Development Agency (SIDA) for providing the financial support that
made possible the study.
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Received 1 May 1997
1. Swedish University of Agricultural Sciences, Uppsala, Sweden
2. Finca Ecologica, University of Tropical Agriculture, Thu Duc, Ho Chi Minh City, Vietnam
3. In the traditional manufacture of crystalline sugar at artisan level the clarified syrup is centrifuged only once to give "A" sugar and "A" molasses. In industrial sugar production, the "A" molasses is recirculated and centrifuged two more times giving respectively "B" and "C" sugar. The residual molasses (from which no more sugar can be crystallized) is known as "final" or "C" molasses. "A" molasses is richer in sugar and has a better feed value than "C" molasses.