The study was carried out from March 2002 to December 2002 at
the Experimental Farm of Cantho University, in the South of
Vietnam, and consisted of on-station trials with growing local
breed (Tau Vang) chicks and hens, and an on-farm trial with growing
chickens, to compare the effect of duckweed on growth and economic
performance of scavenging chickens.
The objectives of the research were to
evaluate the effects of level of dietary protein and duckweed
supply on daily feed intakes and growth rate of chicks and to
determine the optimum level of soybean meal in diets for growing
local chickens and laying hens when duckweed is available
ad-libitum. In the 28-day growth trial, 402
day-old Tau Vang chicks were used in a completely randomized design
with 3 levels of protein (CP18, CP20 and CP22) with or without
duckweed supplement. Then growing chickens of 4 weeks of age were
used in a second growth trial with a completely randomized design
with 5 dietary treatments and 3 replicates. The control diet was a
mixture of broken rice and soybean meal (SB100). For the other four
diets, the level of soybean meal was reduced to 75, 50, 25 and 0%
of the control diet, and duckweed was available ad-libitum,
giving 5 diets (SB0DW, SB25DW, SB50DW, SB75DW and SB100
respectively) fed to growing chickens from 5 - 15 weeks of age. In
the final experiment hens were selected on the basis of growth rate
and appearance from the remaining chickens used in the previous
growth trial, and continued on the same treatment as in the growth
trial.
The parameters recorded were feed intake, weight gain,
mortality, feed conversion, feathering rate, carcass value, carcass
proportion and economic benefits for the growing chickens, and egg
number and weight, quality of eggs and yolk pigment, proportion of
fertile eggs and hatchability of eggs for the layer
hens.
The results from the experiment with day-old chicks to 4 weeks
of age showed that total daily dry matter feed intakes were
slightly higher on the CP20 and CP22 diets compared with the CP18
diet (P>0.05) and also higher when duckweed was supplied
compared to the treatments without duckweed. CP from duckweed
decreased with increasing levels of protein in the diets. Chicks
fed DW had slightly higher weight gains compared with chicks fed
the diets without DW (P>0.05).
The findings from the experiment with growing chickens from 5 -
15 weeks of age indicated that feed intakes and daily gains were
highest on the SB50 diet for female chickens and on the SB0 diet
for the male chickens, with the lowest daily weight gains were on
the SB100 diet (P<0.05). The proportion of CP of the total
intake that came from duckweed increased significantly from the
SB75DW to the SB0DW diet (P<0.05). Carcass yields were
significantly higher for chicks fed the SB0, SB25 and SB50 diets,
and lowest for chicks fed the SB100 diet (P<0.05). The meat from
chickens feed duckweed was of 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 cost compared to
the diet with 100% of soybean, especially when 100% and 75% of the
soybean meal was replaced by broken rice, and fresh duckweed was
offered ad-libitum.
The findings from the layer experiment showed that total feed
consumption and concentrate intake were not significantly different
among treatments (P>0.05). Duckweed intake on the SB0DW diet was
significantly higher than for the SB25DW, SB75DW and SB50DW
treatments. In consequence, the proportion of the total crude
protein intake from duckweed was highest on the SB0DW diet and
decreased on the SB25DW, SB50DW diets, which were higher than on
the SB75DW diet (P<0.05). There were no significant differences
in daily CP and ME intakes and feed conversion ratio (P>0.05)
among treatments. Age at first egg was not significantly different
among treatments, although was somewhat higher on the SB100 diet
compared to the other treatments (P>0.05). There were no
significant differences among treatments for egg production, egg
weight, fertility, hatchability or egg quality parameters
(P>0.05). However, yolk pigmentation was significantly better
(P<0.05) for all treatments with duckweed compared to the
control diet.
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 provided ad-libitum to all treatment groups. On each farm 60 chickens from 5 weeks of age were divided into 3 groups. Two groups were allowed to scavenge in the gardens with or without duckweed supplement (SCDW and SC) and one group was confined (CFDW) and given duckweed ad-libitum. The results showed that the weight gain was slightly higher on the SCDW diet than on the SC and CFDW diets (P>0.05). The highest economic benefits were on the SCDW diet compared with the SC and CFDW diets.
Key words: Duckweed, Tau Vang chicks, growing
chickens, layer hens, weight gain, feed intake, egg yolk color,
scavenging, economic benefits.