Livestock Research for Rural Development 16 (8) 2004

Citation of this paper

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 (R = 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.

Key words:  Chickens, conversion, duckweed, economic benefits, feed intakes, local, weight gain,  scavenging,


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


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:

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).

Table1.  Composition of the experimental diets (as fed)

 

SB100

SB75DW

SB50DW

SB25DW

SB0DW

Broken rice

65.3

73.3

81.3

89.3

97.3

 Roasted soya beans

32

24

16

8

0

Shell meal

1

1

1

1

1

Bone meal

1

1

1

1

1

Vitamin premix

0.2

0.2

0.2

0.2

0.2

Lysine

0.3

0.3

0.3

0.3

0.3

Methionine

0.2

0.2

0.2

0.2

0.2

Duckweed

0

Ad libitum

Ad libitum

Ad libitum

Ad libitum

Cost (VND/kg)

3110

2942

2774

2606

2438



Table 2. Chemical composition of the experimental diets

 

SB100

SB75DW

SB50DW

SB25DW

SB0DW

Duckweed

Dry matter

89.2

88.9

88.7

87.9

88.7

6.5

As % of DM

Crude protein

19.1

17.8

15.7

13.2

8.9

33.7

Amino acids

 

 

 

 

 

 

   Lysine

1.10

0.98

0.87

0.76

0.63

0.9

   Methionine

1.31

1.24

1.17

1.08

0.98

0.7

   Threonine

1.67

1.55

1.15

1.07

0.87

1.7

Crude fibre

4.8

4.7

2.7

1.6

1.1

7.3

Ether extract

6.5

5.4

4.2

2.7

1.6

5.9

Calcium

0.6

0.7

1.1

1.2

1.3

1.02

Phosphorus

0.4

0.4

0.5

0.3

0.3

1.6

ME, MJ/kg*

13.4

13.4

13.4

13.4

13.4

7.92

*Calculated


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:


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.

Table 3: Composition of the concentrate feed (% as air dry)

Broken rice

89.3

 Roasted soya beans

8

Shell meal

1

Bone meal

1

Vitamin premix

0.2

Lysine

0.3

Methionine

0.2

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 (R = 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.

Table 4.  Mean values for nutrient intakes of growing Tau Vang chickens fed diets in which duckweed replaced  roasted soya beans meal and broken rice

Item

SB100

SB75DW

SB50DW

SB25DW

SB0DW

SEM

P

Feed intake, g/day

 

 

Total DM

 

 

 

 

 

 

 

      Female

30.3

37.4

42.6

39.6

38.8

3.50

0.23

      Male

39.0

44.5

47.6

48.3

49.0

4.80

0.59

Concentrate DM

 

 

 

 

 

 

 

      Female

30.3

34.2

38.4

34.5

31.3

3.31

0.48

      Male

39.0

41.3

42.7

42.9

40.3

4.49

0.97

DW DM

 

 

 

 

 

 

 

      Female

 

 3.2c

4.2b

5.1b

7.5a

0.40

0.00

      Male

 

3.2c

4.9b

5.4b

8.7a

0.50

0.00

Crude protein

 

 

 

 

 

 

 

      Female

 5.7c

  8.5a

   9.0a

8.4b

8.5a

0.70

0.04

      Male

7.4

9.7

10.2

9.7

10.3

1.00

0.27

Crude protein %

 

 

 

 

 

 

 

Of DM intake

 

 

 

 

 

 

 

      Female

19.0b

22.7a

21.1a

21.1a

22.2a

0.67

0.02

      Male

19.0

21.7

21.3

20.3

22.1

0.60

0.06

From DW

 

 

 

 

 

 

 

      Female

 

14.2c

17.9b

23.5b

33.7a

1.20

0.00

      Male

 

12.3c

18.1b

21.7b

32.6a

1.10

0.00

Amino acids, g/day        

Lysine, g

 

 

 

 

 

 

 

      Female

0.33

0.43

0.45

0.41

0.41

0.03

0.08

      Male

0.43

0.49

0.51

0.48

0.5

0.05

0.78

Methionine, g

 

 

 

 

 

 

 

      Female

0.40

0.45

0.48

0.41

0.36

0.04

0.29

      Male

0.51

0.53

0.53

0.50

0.45

0.05

0.83

Calcium & phosphorus, g/day          

Calcium, g

 

 

 

 

 

 

 

      Female

0.28

0.33

0.35

0.32

0.29

0.03

0.41

      Male

0.36

0.39

0.4

0.38

0.37

0.03

0.95

Phosphorus, g

 

 

 

 

 

 

 

      Female

0.16

0.22

0.25

0.23

0.24

0.02

0.64

      Male

0.21

0.26

0.28

0.28

0.3

0.03

0.24

ME, MJ/day

 

 

 

 

 

 

 

      Female

0.40

0.49

0.55

0.50

0.48

0.05

0.24

      Male

0.52

0.58

0.61

0.62

0.61

0.06

0.81

Ca:P

 

 

 

 

 

 

 

      Female

1.71a

   1.47b

   1.43b

     1.35c

   1.19d

0.02

0.00

      Male

1.71a

1.51b

1.43b

1.38c

1.21d

0.02

0.00

abcd Means without common superscripts within rows are different at P<0.05

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

 

Table 5. Mean values for changes in live weight and feed conversion in growing male and female chickens (Tau Vang) fed diets with duckweed replacing  roasted soya beans and broken rice

Item

SB100

SB75DW

SB50DW

SB25DW

SB0DW

SEM

P

Live weight, g

 

 

 

 

 

 

 Initial

 

 

 

 

 

 

 

    Female

290

292

289

307

263

14.5

0.38

    Male

350

334

336

346

341

11.6

0.85

 Final

 

 

 

 

 

 

 

    Female

637c

905ba

1102a

1090a

891b

42.8

0.00

    Male

769b

1033ab

1145a

1156a

1222a

57.4

0.02

Daily gain

 

 

 

 

 

 

 

    Female

5.0b

8.9a

11.7a

11.4a

9.4a

0.7

0.00

    Male

5.9b

  10.0ab

11.7a

11.5a

12.5a

1.0

0.00

FCR, kg DM/kg gain

 

 

 

 

    Female

6.1a

4.3b

3.6b

3.5b

4.2b

0.3

0.00

    Male

6.6a

4.4ab

  4.1b

  4.1b

 3.9b

0.6

0.03

Crude protein conversion, g protein/g LW gain

 

 

 

    Female

1.15a

0.97ab

0.77b

0.74b

0.92b

0.06

0.01

    Male

  1.26a

 0.96b

    0.87b

   0.87b

   0.82b

0.1

0.06

abc Means without common superscripts within rows are  different at P<0.05


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).

Table 7. Mean values for changes in composition of the thigh muscle in male and female chickens (Tau Vang) fed diets with duckweed replacing  roasted soya beans meal and broken rice

Item

SB100

SB75DW

SB50DW

SB25DW

SB0DW

SEM

P

Dry matter, %

 

 

 

 

 

 

 

      Female

25.6a

25.1a

23.9b

24.2b

22.3c

0.30

0.00

      Male

26.7a

24.6b

24.4b

24.2b

24.1b

0.50

0.03

Crude protein, %

 

 

 

 

 

 

 

      Female

79.3

84.4

92.5

85.3

92.7

3.40

0.09

      Male

79.0

90.3

84.4

81.6

86.5

2.60

0.42

Ether extract, %

 

 

 

 

 

 

 

      Female

12.1

7.6

7.1

10.2

7.2

2.00

0.36

      Male

9.5

8.0

8.3

10.6

9.3

2.00

0.90

abc Means without common superscripts within rows are different at P<0.05

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.

Table 8.  Mean values for changes in  feed costs and income  (15,250VND = 1USD) for male and female chickens (Tau Vang) fed diets with duckweed replacing  roasted soya beans meal and broken rice

Item

SB100

SB75DW

SB50DW

SB25DW

SB0DW

Total feed cost, VND

 

 

 

 

 

    Female

6,449

7,507

7,772

6,600

5,762

    Male

8,305

8,744

8,676

8,291

7,365

Income, VND

 

 

 

 

 

    Female

12,744

18,100

22,030

21,800

17,814

    Male

15,386

20,650

22,900

23,120

24,434

Margin of income over feed costs, VND

 

 

    Female

6,295

10,592

14,258

15,200

11,308

    Male

7,081

11,906

14,224

14,829

17,069

 

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).

Table 9.  Mean values for changes in  feed intake of growing Tau Vang chickens given concentrate and duckweed in confinement (CFDW) or scavenging (SCDW), or only concentrate and scavenging (SC)

Item

  CFDW

 SCDW

    SC

      SEM

        P

Feed intake, g/day

Total DM

38.3a

37.4a

34.7b

0.78

0.02

Concentrate DM

35.5

36.1

34.7

0.85

0.52

Duckweed  DM

2.8a

1.3b

-

0.10

0.00

Crude protein

5.5a

5.2b

4.6c

0.10

0.001

Crude protein, %

Of  DM intake

14.1a

13.5b

13.0c

0.20

0.001

As duckweed in total protein

15.5a

7.9b

-

0.90

0.001

abc Means without common superscripts within rows are  different at P<0.05


Live weight and daily weight gain

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

Table 10. Mean values for changes in live weight and feed conversion  (supplementary feed only) of growing Tau Vang chickens given concentrate and duckweed in confinement (CFDW) or scavenging (SCDW), or only concentrate and scavenging (SC)

Item

CFDW

SCDW

SC

SE

P

Live weight, g

 

 

 

 

 

    Initial

250

249

242

15.9

0.93

    Final

1018

1110

1017

63.8

0.52

    Daily gain

10.5

12.4

11.0

1.20

0.56

FCR, kg DM/kg gain

3.04

2.66

2.81

0.29

0.67


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).

Table 10. Mean values for carcass traits of Tau Vang chickens given concentrate and duckweed in confinement (CFDW), or scavenging (SCDW), or only concentrate and scavenging (SC)

Item

CFDW

SCDW

SC

SEM

P

Live weight, g

 

 

 

 

 

     Female

1068

1096

1063

61.9

0.91

     Male

1062

1103

1012

50.4

0.46

Carcass weight, g

 

 

 

 

 

     Female

682

680

644

47.3

0.81

     Male

646

660

650

31.7

0.46

Carcass yield, %

 

 

 

 

 

      Female

63.6

62.0

60.6

1.3

0.24

      Male

60.0

59.9

59.8

1.1

0.74

Liver weight, g

 

 

 

 

 

      Female

26.0 b

32.0 a

32.5 a

1.9

0.05

      Male

28.0b

36.7a

35.0a

1.9

0.02

Gizzard weight, g

 

 

 

 

 

      Female

33.0

36.3

32.5

2.4

0.49

      Male

34.0

33.3

31.7

3.3

0.88

 Caecum length, cm

 

 

 

 

 

      Female

14.2

15.6

14.7

0.4

0.09

      Male

13.5b

17.9a

15.7a

0.9

0.02

  Breast angle, o

 

 

 

 

 

      Female

69.0

73.0

71.0

1.9

0.35

      Male

68.8

67.7

66.3

0.2

0.21

ab Means without common superscripts within rows are different at P<0.05


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:


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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