Effect of offering fresh duckweed (Lemna minor) to chickens fed restricted levels of maize meal and protein conentrate in confinement  

Du Thanh Hang

Hue University of Agriculture and Forestry, Hue
hangduthanh@yahoo.com.vn

Abstract

 

Forty-five Luong Phuong chickens at 30 days of age were randomly distributed into 3 replications of five treatments (3 chickens per experimental unit). The birds were offered a basal diet based on maize and soybean meal (16% crude protein in the DM)  offered ad libitum or restricted to  60, 70, 80 or 90% of the ad libitum intake. On all the diets the birds had free access to fresh duck weed.

 

When the concentrate was freely available, the chickens consumed fresh duckweed in amounts equivalent to 7% of the total DM intake and 15% of the total protein intake,  giving a protein content in the diet DM of 17.5%.  These proportions increased to 15 and 30%, for DM and protein, respectively, and the overall protein content of the diet increased to 19.4%, when the concentrate offer level was reduced to 60% of ad libitum intake. Feed DM intake, live weight gain and feed DM conversion became poorer as the proportion of duckweed in the diet increased, and there was no saving in concentrate usage per unit live weight gain.  Under the conditions of the present study, with a basal diet of maize and protein coentrate (16% protein in DM), there was no advantage in restricting the intake of the concentrate  and providing ad libitum duckweed, as the chickens were unable to eat enough fresh duckweed to compensate for the restriction in the concentrate allowance. 

Key words: Local feed resources, water plants

Introduction

In Central Vietnam, protein-rich feed resources for monogastric animals in general and for chickens in particular are scarce and expensive.  The main protein sources are fishmeal and groundnut cake but the prices are relatively high, and storage is also a problem, particularly in the case of groundnut cake. Possible alternatives to these conventional protein meals are the leaves of forage trees and shrubs and water plants`(Preston 2006).

The potential nutritive value of duckweed (Lemna minor) in poultry diets has long been recognized (Haustein et al 1988; Leng 1999). Duckweed has also received research attention because of its great potential to remove mineral contaminants from waste-waters emanating from sewage works. When effectively managed in this way duckweed can yield from 10 to 30 tonnes DM/ha/year containing up to 43% crude protein, 5% lipids and a highly digestible dry matter (Leng 1999).

Haustein et al (1988) suggested that although earlier studies had included duckweed in poultry feeds at relatively low concentrations (5 to 10% in DM), this was with duckweed of poor quality (high fiber and ash, and less than 20% protein). With higher quality duckweed (from 30 to 40 % protein, low ash, high carbohydrate), Haustein et al (1988) reported that duckweed could substitute most of the soybean meal and fish meal in diets of laying hens. According to these authors, the optimal level of duckweed in the diet was 15% but even at 40%, egg quality was not affected. However, an important point is that in these experiments  the duckweed was dehydrated to a dry meal.

Dehydration of duckweed is rarely feasible at the level of small scale farmers, because of it high moisture content (about 95%). This study therefore aimed to evaluate the feeding of fresh duckweed as a supplement to a maize / concentrate diet.

Material and Methods

Experimental design

Forty-five Luong Phuong chickens at 30 days of age, with average weight 80g, were randomly distributed into 3 replications of five treatments (3 chickens per experimental unit). Over a 30 day experimental period the birds were given a basal diet (based on maize and a 42% protein concentrate) offered ad libitum or restricted to  60, 70, 80 or 90%  of the ad libitum intake. On all the diets the birds had free access to fresh duck weed. The basal diet was ground yellow maize + protein concentrate (X4000 from VIFOCO company with 42% crude protein), mixed in  a 30:70 ratio to  provide 16% crude protein in the DM.

Housing system

Three temporary structures (considered as replications) made of bamboo matting and fence posts were built to house the chickens. Each house was separated into 5 pens measuring 0.5 m x 1m using wooden frames and heavy commercial grade wire mesh. Each pen was provided with two feeders (one for the maize-protein mixture and one for duckweed) and an automatic watering device. 

Feeding system

Duckweed was collected from natural ponds, washed with clean water,  and offered ad libitum according to the following procedure: approximately 70% of the total duckweed offered (the exact amount was recorded) was mixed with the concentrate and offered in four meals during the day in one of the feed troughs. The remaining 30% of the duckweed was offered in a separate feed trough.

Measurements

An adaptation period of 10 days was allowed before starting the collection of data. Feed offered and refused was then measured daily before and after each of the meals. The weight of each chicken was recorded every 5 days. Samples of feed were taken every 5 days and analysed for dry matter and crude protein according to AOAC (1990) procedures. After finishing the 30 day trial, 3 chickens from each treatment were slaughtered to determine the weights of carcass and offals (intestine, gizzard and liver) and to record presence of parasites.
 

Results and Discussion

The average content of crude protein in the duckweed throughout the experiment was 38% in DM, a value at the high end of the range reported by Leng (1999). The intake of duckweed increased as the degree of restriction of the concentrate was increased (Table 1); but this did not compensate for the reduced intake of concentrate, thus total DM intake declined (Figure 1), which in turn led to a reduced live weight gain (Figure 2).  

 

Figure 1: Effect of restricting the concentrate allowance on intake of DM as duckweed and as total diet 

 When the concentrate was freely available, the chickens consumed fresh duckweed in amounts equivalent to 7% of the DM and 15% of the protein in the overall diet, giving a final protein level in the diet DM of 17.4% (Table 2). These proportions increased to 15 and 30%, for DM and protein, respectively while the protein content of the diet increased to 19.9%, when the concentrate offer level was reduced to 60% of ad libitum. However, total feed DM conversion, and also concentrate conversion, became poorer as the proportion of duckweed in the diet increased, thus there was no saving in concentrate usage per unit live weight gain. 

 Under the conditions of the present study, with a basal diet of maize and protein supplement (16% protein in DM) fed to growing Luong Phuong chickens, there was no apparent benefit from including fresh duckweed in the diet, as the principal economic parameters (live weight gain and feed conversion) deteriorated as the level of duckweed in the diet was increased.  This contrasts with reports of studies with dehydrated duckweed (Haustein et al 1968), where complete replacement of the fish meal / soya bean component of the diet reduced performance only slightly.  

Table 3: Effect of reducing the offer level of concentrate on weight of cacass and offals  of Luong Phuong chickens (duckweed was offered ad libitum on all treatments )
	Offer level of concentrate (% of ad libitum)
	60	70	80	90	100	Prob
Means after correction by covariance for differences in final live weight
Cacass, g	1326	1380	1395	1456	1452	0.76
Liver, g	36.2	37.0	34.5	38.5	35.5	0.41
Gizzard, g	49.6	33.0	33.0	26.5	35.6	0.061
Intestine, cm	153	138	131	115	126	0.39
Caecum, cm	10.3	11.5	12.7	12.8	12.5	0.24
Thigh, g	147	165	175	173	178	0.79
Chest muscle, g	158	172	169	194	197	0.48

 The changes in the carcass and digestive tract reflected the lower growth rates when the concentrate allowance was restricted (Table 3). 

In the present study, the basal diet was already relatively rich in protein (16% in DM) and in energy (30% maize grain), thus supplementation of the diet with duckweed effectively reduced the energy content while raising the protein to levels that were probably in excess of  requirements.  Under these conditions, the reduction in performance caused by supplementation with duckweed  was a logical outcome.  Future studies should be with basal diets of high energy but low protein content, in order to provide the conditions for the duckweed to provide a major part of the protein of the diet. 

Conclusions

• Restriction of the basal diet of maize and protein supplement (16% protein in DM),  offered to Luong Phuong chickens, led to increases in the intake of duckweed, but this did not compensate for the reduction in the concentrate intake, thus total DM intake declined as did live weight gain.

• Future studies should be with basal diets of high energy but low protein content, in order to provide the conditions for the duckweed to provide a major part of the protein of the diet.

Acknowledgements

The author wishes to thank the MEKARN project, financed by Sida, for providing financial support for this study.

References

AOAC 1990  Official methods of analysis of the Association of Official Analytical Chemist (15^th Edition.), Washington, DC

Haustein A T, Gilman R H, Skillicorn P W, Hannan H, Diaz F, Guevara V, Vergara V,  Gastanaduy A  and Gilman J B 1994 Performance of broiler chickens fed diets containing duckweed (Lemna gibba). Journal of Agricultural Science, Cambridge 122 :285-289

 

Leng R A 1999 Duckweed - A tiny aquatic plant with enormous potential for agriculture and environment. APHP series, FAO, Rome
 

Preston T R 2006 Forages as protein sources for pigs in the tropics. Workshop-seminar "Forages for Pigs and Rabbits" MEKARN-CelAgrid, Phnom Penh, Cambodia, 22-24 August,  2006. Article #2 RetrievedMay 7, 113, from http://www.mekarn.org/proprf/preston.htm