Effects of replacing roasted soya beans by broken rice and duckweed on performance of  growing Tau Vang chickens confined on-station and scavenging on-farm

Nguyen Thi Kim Khang  and Brian Ogle*

Department of Animal Husbandry, College of Agriculture,
Cantho University, Vietnam
khangntkim@yahoo.com
* Department of Animal Nutrition and Management,
Box 7024 Swedish University of Agricultural Sciences,
S-750 07 Uppsala Sweden

Abstract

Two trials were carried out to determine the effect of replacing roasted soya beans with broken rice and duckweed (DW) in diets for growing (Tau Vang) chickens. The first trial was done in confinement at the experimental farm of Cantho University; the second was on farms in Long Hoa village in a scavenging system.

The on-station trial was a completely randomized design with 5 dietary treatments and 3 replicates. The control diet was mixed broken rice and roasted soya beans only  (SB100); the other four diets had duckweed available ad libitum, with soya beans at levels of  0, 25, 50 and 75 of the SB100 diet (SB0DW, SB25DW, SB50DW, SB75DW, respectively), fed to growing chickens from 5 to 15 weeks of age.

The proportion of dietary protein contributed by duckweed increased linearly (R² = 0.96) as the content of soya beans in the concentrate was reduced. Total DM intake and live weight gain showed a positive curvilinear relationship with the proportion of dietary protein derived from duckweed.  DM feed conversion was equally related with  the proportion of dietary protein derived from duckweed.  Optimum values were obtained with 75% replacement of  roasted soya beans  protein by duckweed. 

The meat from chickens fed duckweed had a more intense yellow color than that from birds on the soya bean meal control diet. Feeding fresh duckweed to local growing chickens resulted in decreased feed costs compared to the diet with 100% soya beans, especially when 100% and 75% of the soya beans was replaced by broken rice and fresh duckweed.

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 no differences in growth performance among the treatments. The highest economic benefits were on the SCDW diet.

Introduction

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 that duckweed is an example of a tropical feed resource capable of very much higher protein yields than soya beans. 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; Skillicorn  et al 1993). 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.

Objectives

• To evaluate the effects on performance of replacing roasted soya bean meal by broken rice and duckweed in diets for growing chickens from 5 to 15 weeks of age on-station
  
  
• To evaluate the effects of a duckweed supplement for confined and scavenging Tau Vang chickens on the production performance and economic efficiency on-farm

Materials and methods

Experiment 1: Effects of replacing soya beans by broken rice and duckweed in diets for growing chickens from 5 to 15 weeks of age, on-station

Location

The experiment was carried out in the experimental farm of Can Tho University from April to July 2002 (11 weeks).

Experimental animals and design

The experimental animal was the Tau Vang chicken of 4 weeks of age (n=360). 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 +  roasted soya beans (100%)
• SB75DW: broken rice +  roasted soya beans (75% of SB100), mixed diet plus fresh duckweed
• SB50DW: broken rice +  roasted soya beans (50% of SB100), mixed diet plus duckweed
• SB25DW: broken rice +  roasted soya beans (25% of SB100), mixed diet plus duckweed
• SB0DW: broken rice + no  roasted soya beans (0%), plus duckweed

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 (Tables 1 and 2).

Management and data collection

Local chickens (Tau Vang; n=360) from a previous growth experiment (Nguyen Thi Kim  Khang and Ogle 2004) were allocated at random to the 5 dietary treatments.  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 in the experimental pig farm of Cantho University and harvested every day during the experimental period. The soya beans were roasted for 2 hours to neutralize anti-trypsin factors, and then ground in a hammer mill.

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.

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 methods (AOAC 1994).  Calcium and phosphorus contents of feeds were determined by AOAC procedures (AOAC 1994); amino acids were analyzed by HPLC according to Spackman et al (1958) at CASE (Center of Analysis Service of Experiments) in HoChi Minh City.

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.

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 with rice, with 3 crops/year, and 738 ha of 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 to 10 chickens, which scavenge in the garden. Solving the waste-water problem (animal wastes and human waste) is important and as small ponds are available for irrigation of the fruit trees, duckweed was grown on waste-water to provide a feed source for this experiment.

Experimental animals and design

The experimental animals were local 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 of broken rice and  roasted soya beans available from 17.00 h to  07:30 h
• SCDW: scavenging + supplement (broken rice and  roasted soya beans) with  fresh duckweed available ad libitum between 17:00 h and 07:30 h
• CFDW: confined + supplement (broken rice and  roasted soya beans), and fresh duckweed available ad libitum

Management and collection of data

60 chickens at 4 weeks of age were 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. The birds were wing banded according to treatment for easy recognition. The chickens scavenged from 07:30 h to 17:00 h. The concentrate feed (Table 3) and duckweed were offered separately after the chickens were confined in the evening (treatment SCDW). In CFDW the feed and duckweed were always available in separate feeders. In SC the only supplement available from 17.00 to 07.30 was the concentrate.

Drinking water was supplied during the day when scavenging and at night. Feed and duckweed offered and residues were weighed daily. The weights of the chickens were 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 calculated.

Sampling and analysis procedures

Samples of feed and duckweed were analyzed for dry matter, crude protein, Ca, and P by AOAC procedures (AOAC 1994). Thigh muscles were analyzed for DM, CP and EE (AOAC 1994)..

Statistical analysis

For both experiments, data were analyzed by variance analysis using the General Linear Model (GML) option of Minitab version 13.3 (2000). Where applicable, pair-wise comparisons using the Tukey test were done on between-treatment means. Regression analysis was performed on certain criteria using proportion of protein from duckweed as the independent variable.

Results

Experiment 1

Feed and nutrient intake

The proportion of dietary protein contributed by duckweed increased linearly (R² = 0.96) as the content of  roasted soya beans in the concentrate was reduced (Figure 1 and Table 4). In turn, total DM intake increased curvilinearly as the proportion of duckweed protein in the diet increased (Figure 2). Intakes of lysine and methionine, and of phosphorus tended to be higher on the diets containing duckweed.

Figure 1: Relationship between  roasted soya bean content of the concentrate and the proportion of the total protein contributed by duckweed	Figure 2: Effect on DM intake of replacing  roasted soya beans and broken rice by duckweed

Live weight change and feed conversion

Growth rates and feed conversion showed a curvilinear relationship with the proportion of the dietary protein contributed by duckweed with optimum values when duckweed supplied about 25% of the dietary protein (Figures 3 and 4 and Table 5). A similar relationship was apparent for protein conversion into live weight (Figure 5)

Figure 3: Relationship between  the proportion of the dietary protein contributed by duckweed and rate of live weight gain	Figure 4: Relationship between  the proportion of the dietary protein contributed by duckweed and DM feed conversion

Figure 5: Relationship between  the proportion of the dietary protein contributed by duckweed and crude protein conversion

 

Carcass evaluation and chemical composition of thigh muscle

The dry matter content of the thigh muscle was lower and crude protein content tended to be higher on diets with duckweed than on the control (Table 7). The skin of the carcasses had a deeper orange-yellow color on the diets with duckweed supplement compared to the SB100 diet (Photo 1).

Photo 1:  Carcasses of chickens fed the control diet (left) and with 50% replacement of  roasted soya beans by duckweed (right)

Economic analysis

Feed costs were decreased and income increased as duckweed replaced  roasted soya bean protein and broken rice in the diets (Table 8). No cost was assigned to the duckweed as it was assumed it was produced with family labour of zero opportunity cost.

Experiment 2

Feed and nutrient intake

More duckweed was consumed, and it contributed a greater proportion of the dietary protein,  when the chickens were confined compared with when they were scavenging (Table 9).

Live weight and daily weight gain

There were no differences among treatments for changes in live weight and conversion of supplementary feeds (Table 10)

Carcass evaluation and chemical composition of thigh muscle

The length of caecum  and liver weight were higher on the scavenging treatments than for the confined chickens (Table 10).

Discussion

Experiment 1

Duckweed is rich in protein and the amino acid profile is slightly superior to that in soya beans (Haustein et al 1990). The crude protein content can be as high as 40% and duckweed can reproduce rapidly (Lipstein and Hurwitz 1983; Lipstein and Talpaz 1984; Leng  1999; Bui Xuan Men  2001). It has great potential as feed for poultry, in spite of the high moisture content (Haustein et al 1987;  Leng  1999). The duckweed used in these experiments had an average DM content of 6.5 %. The crude protein content (33.7 %) in DM was lower than that found in an earlier study carried out in the Mekong Delta (Biu Xuan Men 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 biodigester effluent.

There were positive relationships between proportion of duckweed protein in the diet and feed intake, growth and conversion. However, these relationships were curvilinear indicating that most of the improvement came about between the control diet and the diet with 13% of the protein derived from duckweed. This implies that factors in addition to the protein were contributing to improved performance observed with duckweed supplementation.  Duckweed is rich in the precursors of vitamin A; in contrast, commercial supplements of vitamin A may well lose much of their potency under hot and humid tropical conditions. Thus part of the nutritional contribution of duckweed to the diet may have been the result of its value as a source of vitamins.

The more intense yellow colour of the meat and the skin from chickens fed duckweed was almost certainly because of its high carotene content. Similar results were reported with ducks fed duckweed as a replacement for  roasted soya beans (Bui Xuan Men 2001).

The bird's digestive tract adapts to the type and quantity of food available (Klasing 1998). Therefore, the greater weight of the gizzard in birds fed duckweed may be because of the 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.

According to Klasing (1998) protein deposition decreases when poorer quality protein is supplied that does not have a good amino acid balance. This implies that the higher protein content of the meat from the duckweed supplemented birds reflected a superior amino acid profile from the combination of soya and duckweed proteins.

The increased economic benefits from the dietary treatments in which duckweed replaced  roasted soya beans did not take into account the extra labour cost of growing and harvesting the duckweed. In general, in family-based farming systems, labour is not considered as an opportunity cost as it is supplied by family members. In these situations replacing purchased inputs (soya beans and broken rice) with feeds grown on the farm is seen as an advantage.

Experiment 2

In the confinement treatment in the on-farm trial, the duckweed contributed only 7.3% of the diet DM and 15.5% of the protein,  compared with 12% and 22.5%, respectively, for the same dietary treatments in the on-station trial. This implies that the duckweed used on the farms was of lower quality, probably because of inadequate fertilization, as the nutritive value of duckweed is directly related to the nutrient concentration in the growth media (Leng 1999).

Conclusions

The results from the on-station study indicate that:

• Live weight gain, feed conversion and economic benefit, improved as duckweed replaced roasted soya beans in the diet.
  
  
• The optimum replacement level for weight gain and feed conversion was with 75% replacement of the roasted soya beans; however, economic benefit tended to favour the diet with 100% replacement of roasted soya beans by duckweed.
  
  
• A scavenging system with supplementary duckweed and a concentrate feed containing only 8% roasted soya beans (SB25DW) gave good results under village conditions.

Acknowledgements

We are very grateful to the MEKARN project, supported by the Swedish International Development Authority (Sida/SAREC) for the financial support of this study.  This paper is based on research submitted by the Senior Author to the Swedish University of Agricultural Sciences in partial fulfillment of the requirements for the MSc degree in Tropical Livestock Systems.

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Received 19 May 2004; Accepted 18 June 2004

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