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.
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
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
SB50DW: broken rice + soybean meal (50% of SB100), mixed diet plus
SB25DW: broken rice + soybean meal (25% of SB100), mixed diet plus
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.
3.1. 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).
4.1. 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.
The results from the on-station and on-farm study indicate that:
AOAC.1994. Official methods of analysis of Association of Official Analytical
Chemists. Washington, D.C.
Haustein, A.T., Gilman, R.H., Skilicorn, P.W., Ventura, G. 1987. Safety and
efficacy of Sewage grown Lemna as a protein source for chickens. 6340
Sunny Spring, Columbia, Maryland 21044.
Haustein, A.T., Gilman, R.H., Skilicorn, P.W., Hannan, F.Diaz., Guevara, V.,
Vergara, V., Gastanaduy, A., Gillman, J.B. 1994. Performance of broiler
chickens fed diets containing duckweed (Lemna gibba). Journal of
Agricultural science, Cambridge 122, 285-289.
Haustein, A.T., Gilman, R.H., Skilicorn, P.W., Verara, V., Guevara, V.,
Gastanaduy, A. 1990. Duckweed, a useful strategy for feeding chickens:
performance of layers. Poultry Science 69, 1835-1844.
Klasing, K.C. 1998. Comparative Avian Nutrition. Library of Congress
Cataloging in Publication data. British Library, London, UK.
Leng, R.A. 1999. Duckweed - A tiny aquatic plant with enormous potential for
agriculture and environment. FAO Animal Production and Health.
Lipstein, B., Hurwitz, S. 1983. The nutritional value of sewage-grown samples
of Cholorella and Maicractinium in broiler diets. Poultry Science 62, 1254-
Lipstein, B., Talpaz, H. 1984. Sewage-grown algae as a source of pigments of
broilers. British Poultry Science 25, 159-165.
Martin, R. 1999. Soybean meal quality. ASA. Http://www.asa-europe.org/pdf/
Men, B.X. 2001. Use of duckweed as a protein supplement for growing ducks.
Doctoral thesis. Swedish University of Agricultural Sciences. Uppsala 2001.
Minh, D.V. 1999. Effect of energy and protein supplementation stratergy on the
performance of local and improved scavenging hens in Northern Vietnam.
MSc. Thesis. Swedish University of Agricultural Sciences. Department of
Animal Nutrition and Management.Uppsala.
Minitab statistical software version 13.31. 2000. User's guide to statistics.
Minitab Inc., USA.
NRC. 1994. Nutrient Requirements of Poultry. Ninth revised edition. National
Academy Press. Washington, D.C.
Preston, T.R. 1995. Tropical Animal Feeding. FAO. Animal Production and
Samnang, H. 1998. Pasture Versus Integrated Farming System As Scavenging
Source For Local And Exotic Chickens. Livestock Rural Development.
Volume 10, number 3.
Siregar, A.P., Cumming, R.B., Farell, D.J. 1982a. The nutrition of meat-type
ducks. II. The effects of variation in the energy and protein contents of diets
on biological performance and carcass characteristics. Australian Journal of
Agricultural Research 33, 365-375.
Skillicorn, P., Spira, W., Journey, W. K. 1993. Duckweed Aquaculture - A new
aquatic farming system for developing countries. Washington, D.C.
Spackman., D.H., Stein, W.H.,Moore, S.1958. Automatic recording apparatus for
chromatography of amino acids. Analysis Chemistry 30, 1190.