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Role of scavenging poultry and duckweed production in farming systems |
Poultry production in Vietnam is based on agricultural
production, and accounts for 19% of the total livestock production,
being second only to pig production (Vang et al., 2000).
Most chickens are kept by small farmer households, who typically
raise 10 - 12 birds by scavenging, supplemented by agricultural
by-products. The meat and eggs are either for home consumption,
thus improving the daily diet directly, or for sale. However, the
efficiency of chicken production is low mainly because of the
limited protein content in poultry diets at the level of
small-scale farmers (Dong et al., 1994).
The use of duckweed as poultry feed has been recognized by many
authors (Haustein et al., 1987, 1990; Islam et al.,
1997; Rodriguez et al., 1997, Leng, 1999; Samnang, 1999).
Duckweed has a high crude protein content and a well-balanced amino
acid profile and is also a good source of vitamins and minerals for
livestock (Landolt et al., 1987; Men et al., 2001).
Even though the moisture content of duckweed can be the first
limiting factor for chickens, duckweed can play important role in
poultry feeding.
Therefore, the present study was carried out to evaluate the
effects of level of dietary protein and duckweed 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.
2.1. Role of scavenging poultry and duckweed
production in farming systems
Scavenging chicken systems are a popular and widespread
traditional farming system in developing countries throughout the
world. There are about 3 billion chickens, kept by villagers in
developing countries (Roberts, 1995). In Africa, they account for
more than 70% of the poultry population (Sonaiya, 1990), and in
Ethiopia it has been reported that they account for 98.5 and 99.2%
of the national egg and poultry meat production, respectively
(Dessie et al., 1996). In Vietnam, village systems are
estimated to produce about 65% of the total chicken meat, from
about 70 million chickens per annum (Vang et al., 2000).
Local breeds are more suitable for raising in this system, and in
the Mekong Delta, most of the village chickens are local breeds
such as the Tau Vang, Ta, and Tre breeds, because they are well
adapted to the local conditions and are good at finding their feed
by scavenging. Improved breeds such as the Tam Hoang and Luong
Phuong from China have been introduced into the Mekong Delta in
response to the increased market demand for meat and eggs.
Duckweed is tiny water plant that grows very well on stagnant
pond surfaces. It can tolerate high nutrient stress, and appears to
be more resistant to pests and diseases than other aquatic plants
in the area. According to Leng (1999), yields of duckweed were
reported to be in the range of 10 to 30 tons/ha/year of dry matter
and the protein yield from duckweed was from 6 to 10 tons/ha/year.
Therefore, duckweed can be an important component of integrated
farming systems and a useful candidate to be developed as a feed
resource. Duckweed grows rapidly on nutrient-rich wastewater and
produces biomass rich in protein (Leng, 1999; Men et al.,
2001). Duckweed used in this study was grown on ponds fertilized
with effluent from biodigesters of the experimental pig farm of
Cantho University. In the on-farm studies duckweed was combined
with raising catfish using wastewater to fertilize the ponds.
Duckweed used in the experiments had an average DM content of 4.7 % (Paper I and III) and 6.5 % (Paper II), which are similar to the study of Men et al. (2001). The crude protein content (37 %) in dry matter was slightly 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) due to the fact that the duckweed in our studies was grown on ponds enriched with digester effluent. The essential amino acids content in duckweed is relatively high compared to other plant proteins, especially lysine, methionine and threonine (Leng, 1999), which will thus have a positive effect on the growth of chickens. Besides, duckweed also supplies vitamins, especially vitamin A, which is destroyed quite rapidly in hot and humid conditions, and which is essential for growth and reproduction, and would have been supplied by the duckweed, which is rich in carotenoids (Landolt et al., 1987; Solomons, 1996). Moreover, duckweed has a high palatability and could have stimulated the chickens to consume more concentrate (Men et al., 2001). With its high carotene content (1,025 mg/kg DM, Men et al., 2001), duckweed markedly deepened the yellow color of the meat and the skin and also resulted in more intense yellow yolks compared the control treatment.
2.2. Factors affecting intake of
chickens
2.2.1. Effect of body weight and daily gain on feed
intake
Smith (2001) stated that feed consumption is higher in heavy
birds than in light birds, and also that the requirements for males
are higher than for females (Han and Backer, 1994). In the growth
trial, birds with higher body weight gain ate more feed, and
consequently had higher DM, CP and ME intakes (Paper I, II).
However, the male chickens obviously have a greater appetite and
consumed more concentrate feed to exploit the genetic potential for
weight gain compared to the female chickens (Paper II). According
to Smith (2001), the efficiency of feed utilization has a close
relationship with the growth rate (Smith, 2001) because a greater
proportion of the food is used for production when growth rates are
high. Lower daily gains are correlated with higher feed, CP and ME
conversion ratios, and significantly lower carcass weight (Paper
II).
2.2.2. Effect of feed selection
Poultry can attain maximum potential growth rate only when
sufficient high quality balanced feed is available. However, they
can select a balanced diet from among several imbalanced feeds
(Funk, 1932; Graham, 1932 cited by Forbes, 1995) and can
approximately meet their protein requirements by taking appropriate
amounts of high and low protein feeds. In Paper I, chicks offered
duckweed on the CP18 treatment consumed more duckweed than on the
CP20 and CP22 diets and thus the overall protein intake was close
to meeting their requirement. Gous et al. (2000) reported
that broiler chickens, when provided with 2 or 3 foodstuffs each
containing just one protein source on a free choice basis, which in
some proportion will meet their requirements, effectively select a
combination that maximizes their biological performance. The
results in Paper II confirm this, as females and males had the
highest feed intakes on the SB50DW and SB0DW treatments and were
thus able to maximize their growth.
Scavenging chickens can get a high proportion of their total
protein intake from insects and other invertebrates (Smith, 2001)
and therefore supplying extra energy is necessary for scavenging,
not only to balance their total intake with respect to energy and
protein, but also to cover the energy expended in moving around to
find feed (Gunaratne, 1999). In the on-farm trial (Paper II) the
birds, when released to scavenge, were observed to move around
continually in their search for feeds. Samnang (1999) reported that
semi-scavenging chickens given supplements of duckweed and soybean
consumed an energy feed (broken rice) in greater quantities than
the protein supplements. The results in the on-farm trial (Paper
II) show that total concentrate intakes were significantly higher
on the treatments with duckweed compared to the SC
treatment.
2.2.3. Effect of nutritional
deficiencies
The uptake of nutrients depends on the effective activities of
enzymes and coenzymes from the gastrointestinal tract. Severe
deficiencies of essential amino acids, vitamins and minerals affect
feed intakes of chickens, and therefore, feed consumption is
reduced (Liem et al., 2003), and the performance is low
(Leeson et al., 1987; Forbes, 1995). Plavnik (2002) found
that the requirements for the individual amino acids are reduced
when the total dietary amino acid level is reduced because of
growth retardation resulting from single or multiple amino acid
deficiencies. The results of Paper II show that the amount of
lysine intake on the SB100 diet was lower than the other diets,
which could explain the lower feed consumption and the weight gain
of chickens on the SB100 diet. However, the performance of chickens
is improved by addition of deficient amino acids (Ishibashi, 1998),
as would have been the case with duckweed in the diet.
2.2.4. Quality of supplement feeds
The poor nutrient composition of a feed may restrict intake and
prevent the young bird achieving its potential growth. With low
protein content in diets, the feed consumption of chickens is
decreased (Fernaùnder et al, 2002). In Paper I, total
feed intakes of birds fed the CP20 and CP22 diets were higher than
on the CP18 diet. In addition, the digestibility and balance of
amino acids present in feed depend on the quality of the protein
supplement in the diet. The result from the growing and laying
trials show that duckweed with its balanced essential amino acids,
is more effective when supplemented in diets with a single protein
source such as soybean.
2.2.5. Other factors affecting intake
There are many factors that affect intake of chickens. The
results of Paper III show that intake per hen will also be
influenced by mortality within the pen, as the effect of the
cockerel will be greater. Egg output also has a major effect on
feed intake and thus the birds with higher egg production rates
also had higher feed DM intakes. However, if ambient temperature is
very high (³31oC) this may have a negative effect
on the feed intake of laying hens.
2.3. Effects of duckweed on production
Duckweed had a generally positive effect on daily gains, and
even on the 22% CP plus duckweed treatment daily gains were
somewhat higher than on the corresponding CP diet without duckweed.
However, recent studies have demonstrated that on conventional
diets for young broiler chickens growth is retarded as levels of
duckweed (25%) increased (Haustein et al., 1992, 1994). On
the diet in which 100% of soybean meal was replaced by broken rice
and duckweed (Paper II), the chickens tended towards reduced weight
gains compared to the SB25DW and SB50DW diets. The explanation for
this is probably that the birds were unable to consume sufficient
duckweed, due to its bulk and high moisture content. The maximum
growth rate was found on the SB25DW diet. Interestingly, when this
diet was evaluated in the on-farm experiment, in which the
duckweed, was supplemented to scavenging chickens it resulted in
better growth rates compared to the confined group given duckweed
and to the scavenging group without a duckweed supplement. Also in
the laying period, when 75% of the soybean meal in the diet was
replaced by broken rice and duckweed not only was egg production
higher, but also the fertile egg rate and hatchability were
improved. However, the high egg production on the SB0DW diet
confirmed the study of Haustein et al. (1987), who reported
that hens produce significantly better than younger chickens when
fed diets containing high levels of duckweed.
2.4. Advantages of local breeds in scavenging
systems
Local breed chickens are mainly raised in scavenging systems
that are still popular in the rural areas, due to the fact that
they can more easily withstand the harsh climatic conditions and
are less affected by diseases, parasites and poor nutrition and
management than improved breeds. They are easy to rear, find their
feed, and can utilize locally available feed resources such as
duckweed and water spinach. Rodriguez and Preston (1999) reported
that local chickens ate much more fresh duckweed than exotics (Tam
Hoang breed from China). In an earlier study of Khang (2001), the
weight gain of a local breed was found to be better than of exotic
chickens under semi-scavenging conditions because they were more
aggressive and active in finding feed in the garden than the
exotics. Another advantage of raising local chickens in scavenging
conditions is the reduced feed costs and labor to take care of
them. In addition the meat and eggs of local chickens are in high
demand in the market, with for example a meat price of 2.5 times
higher compared to industrial chicken meat (Vang et al.,
2000), because the delicate flavor is preferred by
consumers.
2.5. Inputs and outputs, economic
analysis
Replacing soybean by broken rice and duckweed increased growth
rate and egg production of chickens compared to the SB100 diet and
as duckweed and broken rice are low-cost feeds compared to soybeans
therefore the economic benefits were higher on all the duckweed
treatments. The lowest feed costs per kg live weight were on the
SB0DW diet for both female and male chickens. However, the highest
net incomes were on the SB25DW and SB0DW diets, and the lowest
income was on the SB100 diet. This trend continued into the layer
period, with the SB50DW diet resulting in the lowest cost compared
to the other treatments, but the highest profit was on the SB25DW
diet and the lowest benefit was again on the SB100 diet. In
scavenging conditions, the net economic benefit for the farmers was
highest on the SCDW diet due to better performance as a result of
scavenged protein-rich feed sources such as earthworms, insects and
green grasses and weeds.
From the results of these studies it can be concluded that:
The author gratefully acknowledges the Swedish Agency for
Research Cooperation with Developing Countries (Sida-SAREC) and the
Swedish University of Agricultural Sciences for financial and
material support of this study.
I would also like to express my sincere gratitude to my
supervisor Dr. Brian Ogle for his professional guidance,
constructive criticism and enthusiastic help.
I am greatly indebted to Dr. Inger Ledin, Dr. Luu Trong Hieu,
and Dr. Le Viet Ly for their encouragement.
I would like to express my sincere thanks to Dr. Preston and Dr.
Xe for help in the statistical analysis.
I would like to express my sincere thanks to my teachers Mrs.
Minh, Mrs. Men, Mrs. Loan, Dr. Men, Dr. Son, Mr. Thong, my
colleagues and Thoai, Giau, Nghiep, and Duong, students at the
Department of Animal Husbandry of Cantho University for helping me
to run the experiment, for guidance and for performing the chemical
analyses in the laboratory.
And last but not least, a special thanks to my family for their
help, and to my husband for his love and patience.
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