Effect on growth, apparent digestibility coefficients and carcass quality of local Muscovy ducks of feeding high or low protein duckweed (Lemna minor) as replacement for soybean meal in a rice bran basal diet

Dang Thi My Tu, Nguyen Thi Kim Dong* and T R Preston**

Department of Agriculture Science, Mekong University, Vietnam
tudangmk@yahoo.com
* Department of Agriculture and Applied Biology, Cantho University, Vietnam
** TOSOLY, AA#48, Socorro, Santander, Colombia

Abstract

The experiment was done with 72 local Muscovy ducks fed the experimental diets over a period of 84 days. Measurement of coefficients of apparent digestibility was carried out over the period 70 to 75 days; growth performance was measured over the whole period of 56 days (8 weeks). The ducks were bought at 1-day of age from smallholder breeding flocks in Cantho city and fed a commercial diet from 1 to 28 days of age. The treatments were: CTL, a basal control diet including rice bran with soybean meal; HPDW, rice bran with high protein duckweed; LPDW, rice bran with low protein duckweed. The three dietary treatments contained the same level of crude protein of 15% in DM. A premix (vitamins and minerals) was supplied at 2% of the CTL diet. In treatments HPDW and LPDW it was assumed that the duckweed would provide the necessary vitamins and minerals. The HPDW was cultivated in ponds supplied with biodigester effluent according to the optimum treatment in the earlier experiment (paper 1). For LPDW, the duckweed was collected from natural ponds of local farmers.

Final live weight and daily live weight gain were highest when the supplementary protein was from high protein duckweed and lowest when low protein duckweed was the supplement. The growth rate on rice bran supplemented with soybean meal was lower than for rice bran supplemented with high protein duckweed. There were few differences in carcass traits when the ducks were slaughtered, except for a more attractive skin color for the ducks fed duckweed. The heavier gizzard in ducks fed duckweed probably reflected the higher fiber content of these diets. N retention was highest on the high protein duckweed diets and lowest for the low protein duckweed diets. The better economic results on the high duckweed diet resulted from lower feed costs and higher weight at slaughter.

Key words: Biodigester effluent, fiber, NDF, N retention

Introduction

Poultry production is a common activity in Southeast Asia, and is a major source of livelihood for over a million people in the rural areas. In the last two decades, Asian duck production  has become more important, making up 87% of the world's duck population, and duck meat and egg production has increased  more than four  times (Chein Tai and Jui-Jane Liu Tai, 2001). This expansion has mainly come from the preservation of local breeds and strains, such as the local Muscovy duck and several Vietnamese breeds such as the Co and Tau duck (Duong Thanh Liem 2001), and imports of exotic and improved breeds.

Duck production is one component of integrated farming systems which are regarded as being part of a sustainable development in agriculture. Ducks (Anasplatyrhynchos) can be integrated with rice, orchards, cash crops, livestock and fish. Thus, the stakeholders not only can develop their livelihoods without accumulating debts, but also can get extra income through off-farm and non-farm activities (Le Thanh Phong et al 2007). The Mekong Delta, located in the South of Vietnam, is considered as the country’s granary, accounting for 48% of the national rice production (followed by the Red River Delta). Mekong Delta has a warm ambient temperature and high annual rainfall that is suitable for duck production. Natural resources, including paddy rice fields, canal networks, and plant and grasses, for instance, are advantageous for ducks to increase in number. Ducks can effectively utilize low quality feed (agricultural residues, by-products and insects) and can produce highly nutritional foods for humans (Bui Xuan Men et al 1998).

Duck production is diversified into several raising systems according to economic criteria, for example, industrial integrated, medium to large commercial, medium to small commercial and mixed farming systems (integration of rice-ducks, ducks-fish or rice-fish-ducks) or spatial criteria, such as scavenging, semi-confined and confined systems (Edan et al 2006). The large scale system has developed only recently in some areas of the delta. It is generally agreed that better breeds, together with improvements in management of stock health and using local feed resources, as well as other appropriate technologies should enhance sustainable small-scale duck production.

However, the free-raising of ducks in the rice fields or canals (scavenging system) without strict management of outbreaks of diseases is a risk for community health and also duck production. In order to deal with this important issue and create a sustainable duck production, semi-confined and confined systems are being introduced and widely extended, with the aim of limiting the spread of infectious diseases such as Duck Plague and Avian influenza.

Annually, rice mills produce large quantities of grain for export, as well as the by-products (rice husk, rice bran and broken rice). The broken rice is not as valuable as rice grain but it also can be exported or used locally for human consumption. Rice bran is the outer layer of the brown rice kernel (after separating the husk) which is removed while milling brown rice to white. Rice bran is a rich source of nutrients and a pharmacologically active compound and is currently used as livestock feed and for oil production (Tahira et al 2007). According to Houston (1972), rice bran often occupies 5-8 percent of paddy rice (whole grain). Commonly, in Vietnam, the rice mills have produced three kinds of rice bran: the initial bran (mixed with rice husk fragments) and two types of bran produced in the polishing process which are very fine and have higher nutritive value than the initial bran. In the Mekong Delta, rice bran is cheaper than paddy rice and broken rice so it is the most widely available feed resource for duck production.

Objectives

• To evaluate the use of duckweed as a replacement for soybean meal in a basal diet of rice bran on the growth performance and carcass traits of growing Muscovy ducks.
  
  
• To determine apparent nutrient digestibility and nitrogen retention of Muscovy ducks fed experimental diets.

Materials and Methods

Location and climate of the study area

The experiment was carried out in the experimental farm of Cantho Univeristy in Binh Thuy District, Cantho City and the laboratory of the Department of Agriculture and Applied Biology, Cantho University, Vietnam, from July to October 2011.  The climate is divided into two seasons: the rainy season (from May to November) and the dry season (from December to April). The ambient temperature fluctuates between 22⁰C and 25⁰C in the coolest months (December-January) and 32-33⁰C in the warmest months (April-May). Annual rainfall is 1400-2400 mm, and the average humidity varies from 76 to 80%.

Birds, experimental design and treatments

The experiment was done with 72 local Muscovy ducks fed the experimental diets over a period of 84 days. Measurement of coefficients of apparent digestibility we carried out over the period 70 to 75 days; and (ii) growth performance was measured over the whole period of 56 days. The ducks were bought at 1-day of age from smallholder breeding flocks in Cantho city. They were fed a commercial diet from 1 to 28 days of age. The birds were identified and then individually weighed (average initial live weights were around 950 g). All the birds were vaccinated with Duck Plague vaccine and Pasteurellosis vaccine at three and four weeks.

The experiment was arranged as a completely randomized design with 3 diets (Table 1) and 4 replications, and 6 birds per replicate (3 males and 3 females). The treatments were: CTL, a basal control diet including rice bran with soybean meal; HPDW, rice bran with high protein duckweed; LPDW, rice bran with low protein duckweed. The three dietary treatments contained the same level of crude protein of 15% in DM. A premix (vitamins and minerals) was supplied at 2% of the CTL diet. In treatments HPDW and LPDW it was assumed that the duckweed would provide the necessary vitamins and minerals.

Tu The HPDW was cultivated in ponds supplied with biodigester effluent at the rate according to the optimum treatment determined by Dang Thi  My Tu (2012). For LPDW, the duckweed was collected from natural ponds of local farmers.

The feeding trial started when the ducks were 28 days old and lasted to 84 days of age. Apparent total tract digestibility was measured from day 70 to 75 using 2 ducks from each of the treatments.

Housing and management

The ducks were confined in pens constructed from bamboo, with thatched roofs, wire floors and surroundings with nylon nets (Photo 1).  The average density was 3 birds per m².  Natural light was used in the day and electric bulbs at night to allow eating as well as to deter mice. Feeders and drinkers were put in each pen.  The housing, feeders and drinkers were cleaned and duck manure removed daily in the morning. 

Diets and feeding

In the preliminary period (from day 1 to day 28 after hatching) the ducklings were fed a commercial starter diet ad libitum, which contained 12.2 ME MJ/kgDM and 21% CP. The ducks were kept in groups of 6 from 28 to 84 days. The high protein duckweed was cultivated on ponds enriched with nutrients by providing biodigester effluent at the level of 12 %  which gave the highest biomass yield and CP content according to Dang Thi My Tu (2012). The low protein duckweed was collected from natural ponds which received no fertilizer.  Both sources of duckweeds were harvested daily in the early morning. After collection they were put in large plastic baskets and cleaned by a strong water jet and then left for one hour to drain the excess water.

The rice bran and soybean meal were bought on one occasion from a feed store in the city and used during the whole experiment. For treatments HPDW and LPDW, the duckweeds were mixed with the rice bran in proportions to ensure a CP content of 15% in DM. The ducks were given fresh feed ad libitum 4 times a day at 07:30, 11:00, 14:00 and 19:00 h. Water was freely available for the ducks during day and night. The refusals and spillages were collected and weighed daily in the morning to calculate the feed intake. Samples were taken two times per week for analysis of chemical composition. The rice bran, soybean meal and duckweed were analyzed at the start of the experiment. The duckweed was analyzed two times per week.

Sampling procedure for excreta

During the 5-day collection period, samples were taken of the diets. Excreta were quantitatively collected three times daily at 7:00, 13:00 and 18:00 h, then frozen at - 20⁰C. Care was taken to avoid contamination from feathers, scales and debris. Before analysis, excreta was thawed, then pooled within each diet and replicate and dried for 24 h at 55-60⁰C. The dried excreta was weighed, homogenized, and ground to pass through a 0.5mm sieve, and representative samples were taken and stored in airtight plastic containers at -4⁰C for analysis (Ravindran et al 1999).

Measurements and data collection

Feed and nutrient intakes

Daily feed intakes were calculated according to the total feed consumption of the 6 birds in each pen and nutrient intakes were calculated based on feeds consumed and their nutrient concentrations.

Growth parameters

At the beginning of the experiment all 6 ducks per experiment unit were weighed individually and then weekly.

Carcass parameters

At the end of the experiment in the morning before feeding, one male and one female bird from each pen were slaughtered for evaluation of carcass traits and internal organs. Breast muscles were removed to measure DM, CP, EE and ash.

Economic analysis

Economic analyses were done by using current prices in Vietnamese dong (VND) to calculate the differences in total income and total expenses (including feeds, ducklings, labour, vaccines and medicines) and net profit per treatment.

Chemical analysis

Rice bran, soybean meal, the two kinds of duckweeds, feeds offered and refusals were analyzed for dry matter (DM), organic matter (OM), crude protein (CP), crude fiber (CF), ether extract (EE) and ash by standard AOAC methods  (AOAC1990). Analyses of neutral detergent fiber (NDF) followed the procedure of Van Soest et al (1991). 

Statistical analysis

The data were subjected to analyze of variance (ANOVA) by using the General Linear Model (GLM) of Minitab Reference Manual Release 13 (Minitab 2000). Sources of variation were: treatments and error.

Results and discussion

Growth performance

Chemical composition of dietary ingredients

The duckweed from the fertilized ponds (HPDW) contained about 30% more protein than the duckweed harvested from natural un-fertilized ponds (Table 3). The low calcium content of the rice bran was compensated by the high calcium content of the duckweed. Similarly the high phosphorus content of the rice bran balanced the moderately low content of phosphorus in the duckweed. These results justified the decision not to provide a mineral supplement in the diets containing duckweeds.

Feed intakes

Intake of rice bran, total DM and crude protein were highest for the high protein duckweed (HPDW) and lowest for the low protein duckweed (LPDW). The crude protein content of the diets was almost the same (15.1 to 15.3% in DM).

Daily gain and feed conversion ratio

Final live weight and daily live weight gain were highest on the HPDW diet and lowest on the LPDW diet, with the control diet being intermediate between the two duckweed diets. The differences in growth rate can be explained mainly by the differences in feed DM intake (Figure 1). As the crude protein of the diets was similar the explanation for the superiority of the high protein duckweed diet could be the result of a superior biological value of the protein in the duckweed fertilized with biodigester effluent.

The better growth when rice bran was supplemented with high-protein duckweed rather than with soybean contrasts with the research reported by Bui Xuan Men et al (1996), where growth with 100% duckweed replacing soybean meal was 16% poorer. The differences between the two reports could be due to the quality of the duckweed. In the experiment of Bui Xuan Men et al (1996) the duckweed was produced under small farm conditions, whereas in the present experiment the high-protein duckweed was managed in an experimental farm where conditions were more controlled.

Carcass evaluation

The live weight of the slaughtered ducks differed among treatments (Table 6). When the carcass components were adjusted by covariance for differences in slaughter live weight, there were no differences among the treatments other than for the weights of gizzard (which were lowest on the CTL treatment) and heart (lowest on the LPDW treatment). The lighter gizzard on the CTL diet was probably a function of the lower NDF content of this diet (23.5% compared with 26.2 and 27.2 on the HPDW and LPDW diets).  This result is in agreement with a report that showed that gizzard weights for ducks increased with increasing amount of fiber in the diet (Siregar et al 1982; Dong and Ogle 2003). There is no obvious explanation for the lower heart weight on the LPDW diet. 

Economic analysis and health status

Throughout the experiment, the ducks on all diets were healthy, had good appetite and low mortality (1.4%).

The feed cost and total expenses were the highest for the ducks fed rice bran and soybean meal. The higher income from selling ducks on the HPDW diet was due to the higher slaughter weight, the overall result being higher profit on the HPDW diet (Table 7).  The ducks fed the HPDW diet had a natural yellow color of skin and abdominal fat that is attractive to consumers.

Apparent digestibility coefficients

The chemical composition of feed ingredients in the digestibility period was similar to that in the feeding period (Table 8).

The trends in DM intake during the measurement of digestibility were similar to those observed in the overall feeding trial (Table 9).

Results for nitrogen retention supported the growth performance data with highest N retention for the HPDW diet (Table 10). The higher digestibility of the NDF fraction on the duckweed diets, especially the LPDW diet, probably reflects the differences in the nature of the NDF fraction between rice bran and duckweed, as rice bran represented a lower proportion of the DM in the duckweed diets. It is probable that the NDF in rice bran, which originates mainly from the rice husk, is of lower digestibility than the NDF in duckweed.

Conclusions

• Final live weight and daily live weight gain of Muscovy ducks fed a rice bran basal diet were highest when the supplementary protein was from high protein duckweed and lowest when low protein duckweed was the supplement.

• Rice bran supplemented with soybean meal supported poorer growth than when the supplement was high protein duckweed.

• There were few differences in carcass traits when the ducks were slaughtered, except for a more attractive skin color for the ducks fed duckweed.

• N retention was highest on the high protein duckweed diets and lowest for the low protein duckweed diets.

• The better economic results on the high duckweed diet resulted from lower feed costs and higher weight at slaughter.

Acknowledgements

This research was submitted to Cantho University by the Senior Author in partial requirement for the Master of Science degree “ Specialized in Response to Climate Change and Depletion of Non-renewable resources” We wish to acknowledge the support from the MEKARN Program, financed by Sida.  Gratitude is expressed to the students who helped to carry out this study and to the Department of Agriculture and Applied Biology of Catho University for access to research facilities,

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Received 4 March 2012; Accepted 25 March 2012; Published 2 April 2012

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