Effects of duckweed on the laying performance of local (Tau Vang) hens

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

Eighty local (Tau Vang) laying hens at 19 weeks of age were allocated to 5 dietary treatments and 3 replicates. The control diet was a mixture of broken rice and roasted soya beans (SB100) with no duckweed For the other four diets duckweed was available ad libitum, giving 5 treatments with roasted soya beans at levels of 0, 25, 50, 75 and 100% (SB0DW, SB25DW, SB50DW, SB75DW and SB100 respectively).

Intakes of feed DM and concentrate DM were not different among treatments. Intake of duckweed increased as the roasted soya beans content of the concentrate diet was reduced, contributing up to 29% of the total dietary protein on the zero soya bean basal feed. The crude protein content of the total diet declined linearly (from 16.8 to 12.5% in DM) as the roasted soya beans protein contribution was reduced from 100 to 0%. Age at first egg decreased in a curvilinear response to the proportion of dietary protein contributed as duckweed, with optimum values around the 75% replacement level. Eggs produced per layer in the 56 day period were linearly related with percent protein from duckweed. There was no consistent trend for feed conversion into eggs. Average egg weight and the proportion of total eggs weighing over 38 g tended to show a curvilinear response to the proportion of protein derived from duckweed with optimum values at around 20% as duckweed protein. Both fertility of incubated eggs and hatchability of fertile eggs showed curvilinear relationships with proportion of protein derived from duckweed, with optimum values at around 15% and 25% as duckweed protein for fertility and hatchability, respectively. The yolk pigmentation of the eggs increased in response to protein derived from duckweed. The yolk index of eggs from hens on the SB100 diet was slightly lower (0.38) than the recommended standard of 0.4. Highest production and better fertility and hatchability of eggs from hens consuming the SB25DW diet resulted in highest numbers of chicks hatched and the highest gross income and margin over feed costs..

It is concluded that egg production, egg quality, feed conversion and net profit are highest when fresh duckweed replaces 75% of the protein from roasted soya beans in a diet based on broken rice. Even at 100% of roasted soya beans replacement by duckweed, the egg production and margin of income over feed costs were better than on the control diet in which the supplementary protein came only from roasted soya beans.

Key words: Duckweed, egg production, laying hens, yolk pigmentation

Introduction

In earlier studies (Nguyen Thi Kim Khang and Ogle 2004), duckweed successively replaced the whole of the roasted soya beans in a broken rice basal diet for growing Tau Vang chickens, with improved growth performance.

The objectives of this experiment were to determine the effect of duckweed as a replacement for roasted soya beans on laying and reproductive performance of Tau Vang hens.

Materials and methods

Experimental design

Eighty local (Tau Vang) laying hens at 19 weeks of age were allocated to 5 dietary treatments and 3 replicates. The hens were selected on the basis of growth rate and appearance from the remaining chickens used in a previous growth trial (Nguyen Thi Kim Khang and Ogle 2004), and continued on the same treatments as in the growth trial. The dietary treatments were:

SB100: broken rice + roasted soya beans (100%) with no duckweed (control)
SB75DW: broken rice + roasted soya beans (75% of SB100) plus fresh duckweed
SB50DW: broken rice + roasted soya beans (50% of SB100) plus duckweed
SB25DW: broken rice + roasted soya beans (25% of SB100) plus duckweed
SB0DW: broken rice + no roasted soya beans (0%) plus fresh duckweed

The dry feed component of each diet contained decreasing levels of roasted soya beans and increasing amounts of broken rice (Tables 1 and 2). A vitamin - trace mineral premix was included in all diets. Synthetic lysine and methionine were added to all diets to meet recommended requirements according to NRC (1994).

Table 1. Ingredient composition of the experimental diets
	SB100	SB75DW	SB50DW	SB25DW	SB0DW
Broken rice	67.5	74.5	81.5	88.5	95.5
Soya bean	28.0	21.0	14.0	7.0	0.0
Shell meal	2.0	2.0	2.0	2.0	2.0
Bone meal	2.0	2.0	2.0	2.0	2.0
Vitamin Premix	0.2	0.2	0.2	0.2	0.2
Lysine	0.2	0.2	0.2	0.2	0.2
Methionine	0.1	0.1	0.1	0.1	0.1
Duckweed	0	Ad libitum	Ad libitum	Ad libitum	Ad libitum
Cost (VND/kg)*	2906	2767	2627	2486	2345
* Excluding the duckweed

Table 2. Chemical composition (%) of the experimental diets and duckweed (DW)
	SB100	SB75DW	SB50DW	SB25DW	SB0DW	DW
Dry matter	86.4	89.9	86.1	85.5	86.2	4.7
As % of DM
Crude protein	16.8	14.2	12.3	10.7	9.9	37.3
Amino acids
Lysine	0.79	0.71	0.63	0.53	0.31	0.9
Methionine	0.43	0.41	0.4	0.37	0.31	0.7
Crude fibre	1.91	1.55	1.53	1.4	1.14	5.85
Ether extract	5.34	4.21	2.68	1.17	0.48	9.62
Ash	6.23	6.02	6.1	5.21	5.14	17.91
Calcium	1.50	1.38	1.39	1.29	1.18	0.97
Phosphorus	0.66	0.60	0.60	0.57	0.53	1.53
ME, MJ/kg*	13.2	13.2	13.2	13.1	13.1	9.3
* Calculated

Feeding and management

The laying hens were confined in pens with 5 or 6 hens and one cockerel. The amount of diet offered was 10% (DM basis) of body weight. Feed was weighed daily in the morning. Feed residues were taken every morning and afternoon before feeding. The feed samples were dried and bulked at weekly intervals and stored for analysis. The duckweed was grown on ponds fertilized with effluent from biodigesters on the experimental pig farm of Cantho University and harvested every day during the experimental period. The fresh duckweed was offered ad-libitum in separate feeders and supplied 2 or more times per day. Amounts offered were given with increased frequency according to the recorded intake, to ensure there was minimum wastage of duckweed. The refusals were collected and weighed every morning and afternoon before feeding to calculate the actual intakes of dry feed and duckweed. As there were considerable differences between treatments in the age at production of the first egg, data were collected and analyzed for eight weeks after the first egg for each treatment.

The parameters recorded were:

Feed and duckweed intake
Egg number and egg weight
Quality of eggs and yolk pigment
Proportion of fertile eggs and hatchability of eggs (eggs weighing at least 38 g, laid from around 25 days after first egg and onwards, were collected and tested for fertility [by candling] and hatchability).

Analytical procedures and calculations

Samples of feed and duckweed were analyzed for N, DM, ether extract and crude fibre using standard methods (AOAC 1994). Amino acids were analyzed using HPLC (High-performance liquid chromatography) according to Spackman et al (1958).

Eggs were collected daily and recorded for the entire replicate group throughout the experimental period. Eggs laid during 7 days were kept together and weighed on a replicate basis. Average hen production was calculated from the total number of eggs actually collected divided by the total number of hens present in each group at the end of each week. The records of feed consumption were thus for each week for each replicate.

Shell thickness and albumen height (taken halfway between its outer edge and the outer edge of the yolk) were measured using a micrometer. The indices of albumen, yolk and egg shape (Bao 1978; Smith 2001) were calculated as:

Albumen index = Albumen height/(average of short and long diameter of albumen)
Yolk index = Yolk height/Yolk width
Egg shape = Breadth of egg/length of egg

Yolk pigmentation was measured using the Roche color pan with 1 to14 color score. Yolks numbered 1 to 6 are light yellow, 7 to 10, medium yellow and from 11 to 14 are dark yellow.

Statistical analysis

The data were analyzed by ANOVA using the General Linear Model option of the Minitab software, version 13.31 (Minitab 2000). Comparisons between the treatments were tested by pair-wise comparisons using Tukey's procedure (Minitab 2000).

Results

Feed and nutrient intakes

Intake of duckweed increased as the roasted soya bean content of the concentrate diet was reduced (Table 3), contributing up to 29% of the total dietary protein on the zero soya bean basal feed. However, the crude protein content of the total diet declined linearly (from 16.8 to 12.5% in DM) as the roasted soya bean protein contribution was reduced from 100 to 0%.

Table 3. Mean values for feed intake of Tau Vang laying hens fed diets of broken rice and soya beans replaced by duckweed
	SB100	SB75DW	SB50DW	SB25DW	SB0DW	SEM	P
DM intake, g/day
Total	41.3	47.5	37.5	44.0	54.6	7.47	0.58
Concentrate	41.3	44.9	35.2	40.4	49.4	7.30	0.72
Duckweed	0.0	2.6^b	2.3^b	3.6^ab	5.2^a	0.52	0.00
Crude protein
Total intake, g/day	6.95	7.33	5.21	5.63	6.81	1.12	0.63
From concentrate, g/day	6.95	6.35	4.34	4.30	4.88	1.06	0.33
From duckweed, g/day	0.00	0.98^b	0.86^b	1.33^ab	1.93^a	0.19	0.00
% in diet DM	16.8^a	15.5^b	13.8^c	12.8^d	12.5^e	0.24	0.00
% from duckweed	0.0	13.4^c	16.1^b	23.7^ab	28.7^a	2.25	0.00
Lysine, g/day	0.32	0.40	0.29	0.32	0.30	0.05	0.68
Calcium, g/day	0.62	0.64	0.51	0.55	0.64	0.10	0.87
^abcdeMeans without common superscripts within rows are different at P<0.05

Age at first egg decreased in a curvilinear response to the proportion of dietary protein contributed as duckweed, with optimum values around the 75% replacement level (Table 4 and Figure 1). Eggs produced per layer in the 56 day period were linearly related with percent protein from duckweed (Figure 2). There was no consistent trend for feed conversion into eggs (Table 4).

Table 4. Mean values for egg production and feed conversion of Tau Vang laying hens fed diets of broken rice and soya bean replaced by duckweed
	SB100	SB75DW	SB50DW	SB25DW	SB0DW	SEM	P
Production
FCR, kg feed /kg egg	1.76	2.03	1.69	1.79	2.31	0.33	0.67
Age at 1^st egg, days	191	177	160	144	173	12.7	0.17
Eggs /layer	7.60	9.90	13.5	16.0	16.2	2.90	0.22
Egg weight, g	40.8	42.5	44.9	43.5	41.8	1.65	0.49
% eggs >38g	66.3	62.1	80.7	71	50.7	15.3	0.72
Reproduction
Laying rate, %	16.7	20.7	23.6	28.7	33.0	4.44	0.16
Fertile eggs*, %	66.7	79.2	74.1	75.1	61.0	13.3	0.89
Hatchability^**, %	38.9	70.0	75.4	82.2	68.7	12.2	0.21
* Proportion of fertile eggs from incubated eggs ** Proportion of hatched eggs from fertile eggs


Figure 1: Relationship between dietary protein from duckweed and age at 1st egg	Figure 2: Relationship between dietary protein from duckweed and egg production

Average egg weight (Figure 3) and the proportion of total eggs weighing over 38 g (Figure 4) tended to show a curvilinear response to the proportion of protein derived from duckweed with optimum values at around 20% as duckweed protein..


Figure 3: Relationship between dietary protein from duckweed and egg weight	Figure 4: Relationship between dietary protein from duckweed and percent of eggs weighing > 38g

Reproductive performance

Both the fertility of incubated eggs and the hatchability of fertile eggs showed curvilinear relationships with proportion of protein derived from duckweed, with optimum values at around15% and 25% as duckweed protein for fertility (Figure 5) and hatchability (Figure 6), respectively.


Figure 5: Relationship between dietary protein from duckweed and fertility	Figure 6: Relationship between dietary protein from duckweed and hatchability

Egg quality

The yolk pigmentation of the eggs increased as a curvilinear response to protein derived from duckweed (Table 5 and Figure 7). Albumen index, yolk index and shell thickness were not different among treatments. However, the yolk index of eggs from hens on the SB100 diet was lower (0.38) than the recommended standard of 0.4 according to Bao (1978).

Table 5. Mean values for quality of eggs from Tau Vang hens fed diets of broken rice and soya bean, partially or wholly replaced by duckweed
	SB100	SB75DW	SB50DW	SB25DW	SB0DW	SEM	P
Yolk pigmentation	5.5^b	9.7^a	11.2^a	12.2^a	12.2^a	0.72	0.00
Egg yolk, %	28.5	31.51	29.8	30.6	30.8	1.49	0.68
Shell thickness, mm	0.34	0.35	0.37	0.35	0.36	0.02	0.67
Egg shape	75.5^ab	75.2^ab	73.4^ab	77.7^a	69.2^b	1.54	0.01
Index of Albumin	0.07	0.07	0.06	0.07	0.08	0.01	0.22
Index of Yolk	0.38	0.41	0.41	0.43	0.44	0.01	0.11
^a,b Means without common superscripts within rows are different at P<0.05

Figure 7. Relationship between yolk pigmentation and proportion of protein derived from duckweed

Economic analysis

Size of eggs determine selection for incubation and reached a maximum when duckweed supplied 24% of the dietary protein (SB25DW). Highest production and better fertility and hatchability of eggs from hens consuming this diet resulted in highest numbers of chicks hatched and therefore the highest gross income and margin over feed costs (Table 6).

Table 6. Mean values (per laying hen) for economics of egg production in Tau Vang hens fed diets of broken rice and soybean, partially or wholly, replaced by duckweed during the 8 week experimental period after appearance of the first egg (duckweed cost not included)
	SB100	SB75DW	SB50DW	SB25DW	SB0DW
Total feed consumption, g	2,027	2,296	2,147	2,462	2,966
Feed cost, VND/kg	2,906	2,767	2,627	2,486	2,345
Total feed cost, VND	5,890	6,353	5,640	6,120	6,955
Eggs produced in 8 weeks	7.6	9.9	13.5	16.0	16.2
Eggs weighing >38g	5.0	6.2	10.9	11.4	8.2
Fertile eggs	3.4	4.9	8.1	8.5	5.0
Hatched chicks	1.3	3.4	6.1	7.0	3.4
Eggs weighing <38g	2.6	3.8	2.6	4.6	8.0
Income, VND	8,280	18,159	27,502	33,673	23,386
Sale chicks, VND *	5,217	13,645	24,368	28,093	13,787
Sale of eggs, VND **	3,063	4,514	3,134	5,580	9,599
Margin over feed, VND	2,390	11,806	21,862	27,553	16,431
* 4,000 VND/chick; ** 1,200 VND/egg

Discussion

The duckweed was of good quality, with a crude protein content of 37.3% in DM, probably because the ponds on which it was grown were fertilized with effluent from biodigesters charged with pig manure.. Although the DM content was only 4.7%, the hens on the SB0DW treatment were able to consume 111 g fresh duckweed daily with no reduction in intake of the supplementary concentrate feed. Similar observations were made with ducks offered broken rice and up to 100% replacement of the roasted soya beans by fresh duckweed (Bui Xuan Men et al 1995). The total supply of crude protein on the zero soya bean diet (6.8 g/day) was similar to the that on the control diet (6.95 g/day) with all the protein derived from soybean. According to Kakuk (1988, cited by Liem et al 2003), the daily protein requirement to satisfy reproduction is 5.6 g/day (for hens of body weight of 1.6 kg).

The low egg production of the hens on the control diet could have been due partly to their slower growth rates (see Nguyen Thi Kim Khang et al 2004) prior to selection for the present experiment. Studies by Milby et al (1953) and Leeson et al (1979, 1987) indicated that early growth depression often leads to reduced mature body size and thereby adversely affects adult performance. According to La Thi Thu Minh (1998), age at first egg for local hens in Vietnam is from 160 to 165 days, which is similar to the mean age in our experiment, although the variation was considerable, ranging from 144 days for the SB25DW treatment to 191 days for the controls.

The mean shell thickness on all treatments was higher than the recommendation for local chickens (Bao 1978) of 0.32 mm, which suggests that duckweed had no negative effect on the absorption of calcium. The standard index for egg shape is 75% (Smith 2001), which was met by hens on all treatments, other than the one with 100 replacement of roasted soya beans by duckweed. Yolk colour favoured all the diets containing duckweed as did the yolk index This could be caused by improved supply of vitamin A or xanthophyll (George 1989). Albumin quality was slightly below the standard for all treatments except for SB0DW which could be related to the high temperature (mean maximum of 31^oC), as George (1989) reported that high temperatures reduced albumin index. The second possible reason relates to the time of lay, because the hens were in the first phase of egg production.

The highest economic benefit on the SB25DW diet was a result of the higher rate of egg production, increased egg size and better fertility and hatchability when compared to the other treatments.

As in the experiment with growing Tau Vang hens (Nguyen Thi Kim Khang et al 2004), response to duckweed was curvilinear for most traits with optimum values achieved when duckweed supplied about 25% of the total dietary protein. It is not clear why performance should decrease as between the SB25DW and SB0DW diets, although this infers that a combination of the three protein sources (broken rice, roasted soya beans and duckweed) is superior to the more restricted combination of broken rice and duckweed.

Conclusion

It is concluded that egg production, egg quality, feed conversion and net profit are highest when fresh duckweed replaced 75% of the protein from roasted soya beans in a diet based on broken rice.
Even at 100% of roasted soya beans replacement by duckweed, the egg production and margin of income over feed costs, were better than on the control diet in which the supplementary protein came only from roasted soya beans.

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.

References

AOAC 1994 Official methods of analysis of Association of Official Analytical Chemists. Washington, D.C.

Bui Xuan Men, Ogle R B and Preston T R 1995 Use of duckweed (Lemna spp) as replacement for soya bean meal in a basal diet of broken rice for fattening ducks. Livestock Research for Rural Development. (7) 3: http://www.lrrd.org/lrrd7/3/2.htm

Duong Thanh Liem, Bui Huy Nhu Phuc and Duong Duy Dong 2003 Feed and Animal Nutrient requirements. Agriculture Publishing House. Department of Animal Husbandry. University of Agriculture and Forestry.

George J M 1989 Poultry products technology. Second edition. Food Products Press, Inc. Library of Congress cataloging in Publication Data.

La Thi Thu Minh 1998 Studies on the Tau Vang chickens. Unpublished data, Department of Animal Husbandry.Cantho University.

Leeson S and Summers J D 1987 Effect of immature body weight gain on laying performance. Poultry Science 66, 1924.

Leeson S and Summers J D 1979 Step-up protein diets for growing pullets. Poultry Science 58, 681.

Milby T T and Sherwood D H 1953 The effect of restricted feeding on growth and subsequent production of pullets. Poultry Science 32, 916

Minitab 2000 User's guide to statistics. Minitab Inc., USA.

Nguyen Van Bao 1978 Basis of multiplying and rearing poultry. Scientific and Technical House. Hanoi. (Translated from Wirtschaftgeflugel zucht -

haltung- futterung veb Deutscher landwirtschaftsverlag. Berlin).

Nguyen Thi Kim Khang and Brian Ogle B 2004 Effects of dietary protein level and a duckweed supplement on the growth rate of local breed chicks. Livestock Research for Rural Development. Vol. 16, Art. #54 Retrieved, from http://www.lrrd.org/lrrd16/8/khan16054.htm

Smith A J 2001 Poultry. The Tropical Agriculturalist. Revised edition. Macmillan Education LTD. London and Oxford.

Spackman. D H, Stein W H and Moore S 1958 Automatic recording apparatus for chromatography of amino acids. Analysis Chemistry 30, 1190.

Received 19 May 2004; Accepted 18 June 2004

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