An on-station trial was conducted at the experimental farm of
Cantho University to determine the effect of replacing soybean meal
by broken rice and duckweed (DW) in diets for growing (Tau Vang)
chickens, and an on-farm trial was carried out in Long Hoa village
to evaluate the effect of duckweed on the performance of Tau Vang
chickens in scavenging conditions.
The on-station trial was a completely randomized design with 5
dietary treatments and 3 replicates. The control diet was mixed
broken rice and soybean meal (SB100) only, and for the other four
diets duckweed was available ad libitum, with soybean meal
at levels of 0, 25, 50 and 75 of the SB100 diet (SB0DW, SB25DW,
SB50DW, SB75DW, respectively), fed to growing chickens from 5 - 15
weeks of age.
There was a significant effect (P<0.05) of treatment on feed
intake, and daily gains were highest on the SB50 diet for female
chickens (11.7g) and on the SB0 diet for the males (12.8g), with
the lowest daily weight gains on the SB100 diet (5.0g and 5.9g for
female and male chickens, respectively). The proportion of CP of
the total intake that came from duckweed increased significantly
from the SB75DW to the SB0DW diet (P<0.05), and was thus highest
on the SB0DW treatment (33.7 and 32.6% for females and males,
respectively). Carcass yields were significantly higher for
chickens fed the SB0DW, SB25DW and SB50DW diets, and lowest for
birds fed the SB100 diet (P<0.05). The meat from chickens fed
duckweed was a more intense yellow color than that of birds on the
soybean meal only diet. Feeding fresh duckweed to local growing
chickens resulted in decreased feed costs compared to the diet with
100% soybean, especially when 100% and 75% of the soybean meal was
replaced by broken rice and fresh duckweed was offered
ad-libitum.
The on-farm trial was a completely randomized design with 3
treatments and 4 replications (farms). The SB25 diet from the
on-station trial was selected as the basal diet and given to all
experimental groups. There were in total 60 chickens from 5 weeks
of age on each farm divided into 3 groups of 20. Two groups were
allowed to scavenge in the gardens, with or without a duckweed
supplement (SCDW and SC), and one group was confined (CFDW) and
given duckweed ad-libitum. There were thus 80 chickens in
total for each treatment. Daily weight gain of the birds was
slightly higher on the SCDW diet (12.4g) than on the SC and CFDW
diets (11.0g, 10.50g, respectively) but there were no significant
differences among treatments (P>0.05). The highest economic
benefits were on the SCDW diet (16,186 VND/bird) compared with the
SC and CFDW diets (14,512 and 14,484 VND,
respectively).
Key words: Growing Tau Vang chickens, duckweed, feed
intakes, daily weight gain, carcass yield, scavenging, economic
benefits
Traditional chicken production is still important in the Mekong
delta. Although commercial chickens are raised widely, the local
Tau Vang chickens are becoming more popular due to the fact that
they can withstand the harsh climatic conditions. Also they are
easy to rear, find their feed, and can utilize available feed
resources such as duckweed and water spinach and thus decrease the
cost of production on small farms. Preston (1995) has proposed
alternative sources of protein, and duckweed is an example of a
tropical feed resource capable of very much higher protein yields
than soybeans (Skillicorn et al., 1993). Duckweed can be
produced cheaply, and is a valuable and protein rich biomass,
utilizing unexploited resources such as sewage lagoons or farm
waste ponds (Haustein et al., 1987). Studies have shown that
duckweed (Lemna gibba) had a positive effect on the
growth of broiler chicks when fed at high levels (Haustein et
al., 1990). However, no research has been carried out on the
effect of duckweed (Lemna minor) on the growth and
performance of local Tau Vang chickens in confinement or in
scavenging conditions. Therefore, this study was aimed at
evaluating duckweed in the diet as a protein source for local
scavenging chickens, partly replacing soybean meal.
Objectives
2. Materials and methods
2.1. Experiment 1: Effects of replacing soybean meal
by broken rice and duckweed in diets for growing chickens from 5 to
15 weeks of age, on-station
2.1.1. Location
The experiment was carried out in the experimental farm of Can
Tho University from April to July 2002. The experiment was
conducted for 11 weeks (including 1 week for adaptation) with
growing chickens.
2.1.2. Experimental animals and design
The experimental animal was the Tau Vang chicken of 4 weeks of
age. The design was completely randomized with 5 dietary treatments
and 3 replicates. Each replicate included 24 birds, with 12 males
and 12 females confined in separate pens.
The dietary treatments were:
SB100: broken rice + soybean meal (100%)
SB75DW: broken rice + soybean meal (75% of SB100), mixed
diet plus fresh
duckweed ad-libitum
SB50DW: broken rice + soybean meal (50% of SB100), mixed
diet plus
duckweed ad-libitum
SB25DW: broken rice + soybean meal (25% of SB100), mixed
diet plus
duckweed ad-libitum
SB0DW: broken rice + no soybean meal (0%), plus duckweed
ad-libitum
Duckweed was given ad-libitum on all treatments except
SB100 (control). A premix containing trace minerals and vitamins
was mixed (0.2%) with all diets. The dietary ingredients and
chemical composition are shown in Table 1 and 2.
2.1.3. Management and data collection
In total 360 growing local chickens (Tau Vang) from a previous
chick growth experiment (Paper I) were selected and allocated at
random into 5 groups (the 5 dietary treatments as above). The
chicks were confined in pens with 12 birds per pen. Feed was
weighed daily in the morning and feed residues weighed every
morning and afternoon before feeding. The amount of diet given was
estimated according to the previous day's consumption and was about
10% in dry matter of body weight daily. The fresh duckweed
(Lemna minor) was provided in separate feeders and was added
2 times per day. The feed was given with increased frequency
according to the growth of the birds to ensure there was minimum
wastage. The refusals were collected and weighed every morning and
afternoon before feeding to calculate the actual feed intakes. The
changes in live weight gain were recorded by weighing all chickens
every week.
Representative samples of diets were taken and stored in a
freezer at -20 oC. The dried samples were bulked at
weekly intervals and stored before analysis. The duckweed was grown
on ponds fertilized with effluent from biodigesters of the
experimental pig farm of Cantho University and harvested every day
during the experimental period.
At the end of the trial, the birds were weighed and 2 chickens
of each replicate (1 male and 1 female) were randomly selected,
slaughtered and dressed. Dressing consisted of evisceration, with
only the kidney and lungs left in the carcass. The shanks were
removed at the tibia-tarsal joint, and the head cut off at the
first cervical vertebrate joint. The carcass weight was recorded
and the skin color was estimated. At the end of the trial, the net
economic benefits were calculated.
2.1.4. Chemical analysis
Samples of the experimental diets and thigh meat were analyzed
for dry matter (DM), crude protein (N x 6.25), ether extract (EE)
and ash according to standard AOAC methods (AOAC, 1994) at the
laboratory of Cantho University. Calcium and phosphorus contents of
feeds were determined by AOAC procedures (AOAC, 1994), and amino
acids were analyzed by using HPLC according to Spackman et
al., (1958) at CASE (Center of Analysis Service of Experiments)
in HoChiMinh City
2.2. Experiment 2: Evaluation of a duckweed
supplement on the production and economic efficiency of confined or
scavenging chickens (Tau Vang) on-farm
Based on the results of the on station trial, the diet that gave
optimum live weight gain with the lowest feed costs (SB25DW) was
selected for the on-farm trial, to compare confinement with
scavenging, with or without duckweed.
2.2.1. Geography and climate
Long Hoa village is 10 km from Cantho City with 13,380
inhabitants and 3,000 households in an area of 14 km2.
Around 80% of the total land area is agricultural, with 710 ha
planted rice, with 3 crops/year, and 738 ha fruit-trees. The
economy of the smallholders is based on agriculture. Livestock
production plays an important role in the household economy, and
besides sales, supplies meat and eggs for home consumption. The
population of chickens accounts for 70% of the total of 20,000 head
of poultry. Each household keeps 5 - 10 chickens, which scavenge in
the garden. Solving the wastewater problem (animal wastes and human
waste) is important and as small ponds are for irrigation of the
fruit trees, duckweed was grown on wastewater to provide a feed
source for this experiment.
2.2.2. Experimental animals and design
The experimental animals were chickens at 4 weeks of age. The
design was completely randomized with 3 treatments on each farm and
there were 4 replications (farms). The treatments were as
follows:
SC: scavenging + supplement (broken rice and soybean
meal),
(SB25DW) available between 17:00 h - 07:30 h
SCDW: scavenging + supplement (broken rice and soybean
meal),
(SB25DW) and fresh duckweed available between 17:00 h - 07:30
h
CFDW: confined + supplement (broken rice and soybean
meal),
(SB25DW) and fresh duckweed supplied
ad-libitum
2.2.3. Management and collection of data
A total of 60 chickens at 4 weeks of age was allocated to each
farm and divided into 3 groups. Two groups were allowed to scavenge
in the garden and one group was confined. There were thus 20 chicks
(10 males and 10 females) on each farm for each treatment and the
birds were wing banded according to treatment for easy recognition.
The chickens scavenged all day from 07:30 h to 17:00 h. The feed
and duckweed were offered separately after the chickens were
confined in the evening. Drinking water was supplied during the day
when scavenging and at night. Feed and duckweed offered and
residues were weighed daily. The weight gain of chickens was
recorded every week. At the end of the trial when the birds were 15
weeks of age, all birds were weighed and 2 representative chickens
in each replicate (1 male and 1 female) were randomly selected,
killed and dressed and carcass data collected as described in
Experiment 1. The economic benefits were also
calculated.
2.2.4. Sampling and analysis
procedures
Samples of feed and duckweed were analyzed for dry matter, crude
protein, Ca, and P by AOAC procedures (AOAC, 1994) at the
laboratories of Cantho University. Thigh muscles were analyzed for
DM, CP and EE.
2.3. Statistical analysis
For both experiments, data were analyzed statistically by
variance analysis using the General Linear Model (GML) of Minitab
version 13.3 (2000). Where applicable, pairwise comparisons using
the Tukey test were done on between-treatment means.
3. Results
3.1. Experiment 1
3.1.1. Feed and nutrient intake
The data in Table 3 show that total feed consumption was not
significantly different (P>0.05) between treatments during the
whole experimental period for both male and female chickens.
However, it tended to increase when soybean was reduced in the
diet. The more broken rice and duckweed replaced soybean in the
diets, the more total feed was consumed. Duckweed intake was
significantly higher on the SB0DW diet and decreased on the SB25DW
and SB50DW diets, which were higher than on the SB75DW diet
(P<0.05).
Crude protein intakes were significantly different among
treatments for both male and female chickens (P<0.05) and were
lower on the SB100 diet (5.4 and 7.4 g/day, for females and males,
respectively) than for diets with duckweed. The proportion of CP of
the total intake that came from duckweed increased significantly
from the SB75DW to the SB0DW diet (P<0.05). There was no
significant difference among the treatments for calcium,
phosphorous and ME intakes (P>0.05). The ratio between Ca and
phosphorous was significantly different among the treatments
(P<0.05); the highest ratio of Ca:P was on the SB100 diet (1.7%)
and the lowest on the SB0DW diet (1.2%).
3.1.2. Live weight and daily weight
gain
The data in Table 4 show that the final live weights and daily
weight gains were lowest on the SB100 diet compared to all other
treatments (P<0.01). However, there were no significant
differences among treatments with duckweed (DW) (P>0.05). There
were significant differences for feed conversion ratios among the
treatments (P<0.05), with the highest values for the SB100 diet
(6.1 and 6.6 kg feed/ kg gain, for females and males respectively)
and lowest values for the SB25DW and SB0DW diets for females and
males (3.5 and 3.9 kg feed/kg gain). CP and ME conversion ratios
were significantly higher on the SB100 diet compared to all other
treatments (P<0.05).
3.1.3. Carcass evaluation and chemical composition of
thigh muscle
Data in Table 5 show that carcass weights and carcass yields in
both female and male chickens were significantly higher for chicks
fed the SB0DW, SB25DW and SB50DW diets and lower for chicks on the
SB100 diet (P<0.05).
For both female and male chickens, there were no significant
differences for liver weight and caecum length among treatments
(P>0.05). However, there was a tendency towards heavier livers
on the SB0DW diet compared to the diet without duckweed. The
gizzard weight of males differed significantly among treatments
(P<0.05) and was highest for the SB0DW diet. Breast angle of
females was significantly different among the treatments
(P<0.05) with a higher value on the SB50DW diet
(73.3o) and lower value on the SB100 diet
(60.3o). The skin of carcasses had a deeper
orange-yellow color on the diets with duckweed supplement compared
to the SB100 diet.
The chemical composition of the thigh muscles is shown in Table
6. The differences among the treatments were not significant for %
crude protein (CP) and ether extract (EE) (P>0.05). Dry matter
contents (DM) of thigh muscles were significantly different among
treatments, and were highest on the SB100 diet (25.5% and 26.7% for
female and male chickens, respectively) and lowest on the SB0DW
diet (22.3% and 24.0% for females and males, respectively).
3.1.4. Economic analysis
The results of the economic analysis are given in Table 7, which
shows that the lowest feed costs per kg live weight were on the SB0
diet for both female and male chickens in which the protein
supplement was completely replaced by duckweed and broken rice. The
highest incomes were on the SB25DW and SB0DW diets (15,200 VND and
17,069 VND for female and male chickens, respectively) and the
lowest income was on the SB100 diet (6,295VND and 7,081 VND for
female and male chickens respectively).
3.2. Experiment 2
3.2.1. Feed and nutrient intake
Total feed intakes of DM are shown in Table 8, and were
significantly higher (P<0.05) on the CFDW and SCDW treatments
(38.3 and 37.4 g/day, respectively) compared to the SC treatment
(34.7 g/day).
Total intakes of crude protein, lysine, methionine, calcium and
phosphorus were significantly different among the treatments
(P<0.05) and were higher on the treatments with duckweed.
Duckweed intake was lower on the SCDW diet than on the CFDW diet
(P<0.05). Feed conversion ratio did not differ significantly
among the treatments (P>0.05).
3.2.2. Live weight and daily weight
gain
Results for final live weight, daily weight gain and FCR are
presented in Table 9. The data show that there were no significant
differences for the final live weights and daily weight gains among
the treatments (P>0.05).
3.2.3. Carcass evaluation and chemical composition of
thigh muscle
Data in Table 10 show that carcass weight was not significantly
different among treatments (P>0.05). There were no significant
differences for gizzard weights (P>0.05). The length of caecum
of males was significantly higher on the SCDW diet than on the SC
and CFDW treatments (P<0.05) and liver weights of the males were
significantly higher (P<0.05) on the scavenging treatments
compared to confinement.
3.2.4. Economic analysis
Estimates of the feed costs are presented in Table 11, which
shows that the highest incomes were on the SCDW diet (16,186 VND)
and the lowest incomes were on the CFDW and SC treatments (14,484
VND and 14,515 VND).
4. Discussion
4.1. Experiment 1
Duckweed is rich in protein and the amino acid profile
apparently compares with soybean (Haustein et al., 1990).
The crude protein content can be as high as 37 to 40% and duckweed
can reproduce rapidly (Lipstein et al., 1983, 1984; Leng,
1999; Men et al., 2001). It has great potential as feed for
poultry, in spite of the high moisture content (Haustein et
al., 1987, Leng, 1999). Duckweed used in the experiments had an
average DM content of 6.5 %. The crude protein content (33.7 %) in
dry matter was lower than that found in an earlier study carried
out in the Mekong Delta, by Men et al. (2001) but was higher
than reported by Becerra (1994), probably due to the fact that the
duckweed in our studies was grown on ponds enriched with digester
effluent.
The results in Table 3 show that duckweed intake increased as
soybean in the diets was reduced. This indicates a lack of protein
in the diets and therefore the chickens consumed more duckweed to
meet their requirements, especially for protein, by consuming more
of another protein source with a high protein content and
biological value, in this case duckweed. Another point is the high
palatability of duckweed that could stimulate chickens to increase
their intakes. In an earlier study in the Mekong delta, duckweed
consumption of ducks was higher on a diet without soybeans and
increased to meet nutrient requirements for growth (Men et al.,
2001). The lower feed consumption of chickens on the SB100 diet
could however possibly indicate problems with the effectiveness of
processing the soybeans to destroy trypsin inhibitors (Martin,
1999).
The level of soybean in the diets thus affected protein intake.
However, the total protein intake may also be affected by the
potential for weight gain. The amounts of protein consumed by male
chickens were higher than female chickens because of the higher
requirement for male chickens due to their higher genetic growth potential.
The ratio between Ca and P, according to NRC (1994), to maintain
optimum growth rate of chicks, is 1.6:1, and even though the ratio
on the SB0DW diet was only 1.2, daily weight gain was still quite
good. There were no significant differences in ME intake between
treatments (P>0.05), and Siregar et al. (1982 a), and Men
et al. (2001) have shown that the ME consumed is relatively
constant and independent of concentration of dietary protein and
ME.
The daily weight gain was significantly different among the
diets and the results show that both female and male chickens had
the lowest final live weight and daily weight gain on the SB100
diet. The reduced feed consumption was the main cause of the poor
growth performance. The diets with different proportions of broken
rice and duckweed replacing soybean meal did not give significantly
different daily weight gains, but all were significantly higher
than for the diet without a duckweed supplement (SB100). Haustein
et al., (1994) showed that the weight gains of broiler
chickens fed duckweed (Lemna gibba) were higher than
for chickens fed a standard ration. Higher levels of duckweed
supplement in the diet, however, reduced growth rate of chicks
(Haustein et al., 1994), especially the females. Average
daily gain and feed consumption of female chicks on the SB0 diet
tended to be lower, probably because of the bulkiness and low dry
matter content of duckweed (Men et al., 2001). The results
from this trial suggest that duckweed, with its balanced essential
amino acids, is more effective when supplemented in diets with a
single protein source such as soybean. Lower daily gains are the
explanation for the significantly higher feed, CP and ME conversion
ratios, and significantly lower carcass weight on the SB100 diet
compared to the other treatments.
The meat and the skin from chickens fed duckweed were more
intense yellow than from those on the soybean meal only diet
because of the high carotene content in duckweed (Men et
al., 2001).
The bird's digestive tract adapts to the type and quantity of
food available (Klasing, 1998), and therefore, the gizzard weight
in this experiment tended to be higher on the diets with duckweed
supplement because of higher intakes of fiber. Klasing (1998) also
reported that crop capacity increased on diets high in grass or
leaves compared with a diet based on ground grains. Dry matter
content of thigh muscle was lower on the diets supplemented with
duckweed compared to the SB100 diet due to the lower fat content in
the muscle. According to Klasing (1998) protein deposition
decreases when poorer quality protein is supplied that does not
have a good amino acid balance, and therefore there will be a
higher potential for fat deposition.
The more duckweed consumed, the higher the economic benefits,
due to the lower feed costs and the higher weight gains on the
SB25DW and SB0DW diets (for female and male chickens, respectively)
compared to the SB100 diet.
4.2. Experiment 2
Total intakes of DM, crude protein and other nutrients such as
lysine, methionine, calcium and phosphorus were significantly
higher for the groups given duckweed (CFDW and SCDW) (P<0.05).
Chickens in the SCDW and SC treatments would have found foods with
high protein contents, such as earthworms, insects or green grass
and also trace nutrients when they scavenged all day in the garden
(Haustein et al., 1990; Samnang, 1998; Minh, 1999). These
contributed to meeting their nutrient requirements for growth, and
therefore their concentrate feed intakes were reduced when compared
with the chicks that were confined. Total feed and nutrient intakes
for the confined and scavenging birds were probably similar and
therefore the daily gains on these treatments were not different.
However, as the concentrate intake was only about 10% lower for the
scavenging treatment without duckweed compared to confinement, this
implies that the contribution of scavenging to the total feed
intake was rather low, and that supplement feeds are required for
chickens in scavenging conditions for normal growth.
There was no significant difference among treatments for the
carcass weight and carcass yield, because of the similar weight
gains among treatments. However, the liver weight and the caecum
length were higher on the scavenging treatments. According to
Klasing (1998) the length of caecum increased with increased food
intake or increased dietary fiber. The size of the liver changes
after a meal and also depends on level of nutrition (Klasing,
1998), which could have been higher for the scavenging birds. The
feed cost per kg gain on-farm was slightly higher on the SCDW diet.
However, net income was highest on this treatment due to slightly
higher final live weights.
5. Conclusions
The results from the on-station and on-farm study indicate that:
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