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.
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.
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).
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.
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.
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.
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.
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.
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.
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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