Golden apple snails and Tra fish by-products as protein supplements in diets of fattening ducks                            

Bui Xuan Men and Nguyen Thanh Cong*

Colledge of Agriculture and Applied Biology, Cantho University, Vietnam,
bxmen@ctu.edu.vn
*Agricultural Extension Center, Dongthap province

Abstract

Two on-farm experiments were conducted in Dongthap province and Cantho City of the Mekong Delta in rainy seasons of 2008 and 2009 to evaluate the use of golden apple snails (Pomacea) and Tra fish (Pangasius) by-products as protein supplements to replace the soybean meal in diets of ducklings. In experiment 1, 72 commercial meat ducks (Cherry Valley breed) were used in a completely randomized design, with 3 dietary treatments and 4 replicates. The ducks were fed 0, 50 and 100% of the diet protein from snails replacing that from soybean meal.  In experiment 2, 480 crossbred meat ducks (crosses of Cherry Valley drakes and Nong Nghiep ducks) were allocated to 4 treatments with 3 replicates and 40 ducks balanced for sex per replicate (pen). The dietary treatments were 100% soybean meal (SBM) as protein supplement, 50% of SBM replaced by Tra fish by-products (TF50), 100% of SBM replaced by Tra fish by-products (TF100), and 50% of SBM replaced by golden apple snails (GS50). The diets were offered ad-libitum to the ducks from 21 to 60 days old.

Daily live weight gains of the ducks supplemented with the snails were higher and feed conversion better  compared with ducks fed the SBM diets. Total DM intakes of the ducks offered the SBM and GS50 diets were higher than those fed the TF50 or TF100 diets, the lower intake on the latter reflecting the higher fat content of these diets. Weight gains were depressed with the highest level of TF but did not differ among the remaining. Feed conversion showed the opposite trend with best conversion on the TF 100 diet.

The use of golden apple snails and Tra fish by-products as protein supplements in the diets of meat ducks had several benefits including decreased feed cost, increased employment opportunities (gathering snails in the rice fields and working in the Tra fish processing plants) and decreased pollution (toxic chemicals are otherwise used to kill the snail pests).

Key words: Benefits, feed conversion, growth, pollution, soybean meal

Introduction

Living in the marketing mechanism process the producers in the Mekong Delta are facing with big problems for animal and aquaculture production from high inputs due to  dramatic increases of price of animal feeds and output fluctuations of product prices. At present, if producers use commercial feeds with rather high price to raise ducks they will get very low or no benefits from the activities.

Golden apple snails are seen be seriously damaging pests to the young rice fields and economic loss to rice producers. Also, use of toxic chemicals to eliminate the pests is difficult because of wide distribution of the population, high costs and environmental pollution. Beside the pests water hyacinth plants grow very well in the diches or canals in the Delta. Sometimes it is big problems for water traffic of the boats and use of the plants for animal feeds are rather few.

In recent years fish producers have been encouraged to increase Tra fish production for both for national consumption and export. Yield of the fish produced annually has been over 1 million tonnes (plan for 2020 being 2 M tons) of which 70% is in the form of by-products such as heads, backbone, skin, fat and internal organs. So, a big amount of the by-product could be recycled as energy (from the fat) and as feed (protein and mineral sources for poultry).

In order to maintain the duck production in a sustainable development several ways are carried out to partially replace the traditional system to keep the ducks, of which integrated duck-fish system  has proved to have advantages to apply for producers of the Delta. In the integrated system, ducks will be kept in slat/wire floored houses built over the fish pond and fed several kind of feeds gathered from the village or purchased from local markets. The costs from litter and management will be decreased to minimum. The system is safe for ducks because producers can control and vaccinate against infectious diseases. Wastes (water, mud) from the fish pond can be used as fertilizers for rice or vegetables. Growing plants on the wastes also decreases or eliminates pollution to the environment.

Objectives

• To use Tra fish by products and golden apple snails produced or gathered in the local area as protein supplements to replace imported soybean meal.
• To reduce feed cost for growing ducks to increase benefits for producers.
• To consume the by-products from fish processing plants and to eliminate the snails in the rice fields without toxic chemicals to reduce environmental pollution.
• To create jobs and incomes for household laborers in the agricultural areas.

 Methods and materials

Experimental sites and seasons

The experiments were carried out on farmer holdings in Lapvo district, Dongthap province at the end of the rainy season in 2008 and in Omon district, Cantho City at the end of the rainy season in 2009. The main agricultural products of the farmers in the areas are rice, with some supplementary income from tree fruits, fish and animals (Men et al 2003, 2005, 2007, 2009a, 2009b). 

Experiment 1. Use of golden apple snails as a protein supplement in diets of meat-type ducks.

Experimental design

Seventy-two 28-day-old ducklings were allocated at random to three treatments, with four replicates in one farm at the end of the rainy season in 2008. Each replicate group, consisting of 6 ducks was housed in a separate pen. The ducks were allocated to three diets that contained 16% crude protein (CP), but with different protein sources as follows:.

(1)   Protein only from soybean meal (SBM) as a control diet (SBM100)

(2)   A diet with golden apple snails (GS) replacing 50% protein of the SBM (SBM50)

(3)   A diet with 100% protein replacement of SBM by the GS (SBM00)

These diets were offered to the ducks ad libitum five times per day up to 60 days of age.

The ducks were housed in a shed divided into pens. The pens were made from plastic net attached bamboo frames, with thatched roofs and sand floors covered with rice straw for bedding, and with an average density of one duck per 0.3 m². The ducks also had access to outside covered sand yards combined with small ditches as baths with an area of 1 m² per duck. Feeders used were rectangular plastic basins and drinkers were round plastic containers linked to a plate so that water was filled automatically. Natural and electric light was used to maintain a total of 24 hours light each day.    

Diets and feeding

The chemical composition of the feeds is shown in Table 1. The moisture content of golden apple snails (without shells) was rather high (81.6%). However, the protein content of the GS was very high (56.4% in DM).

The crude protein content in all diets was kept constant at 16% based on 88% of DM of the control diet. However, the amounts as fed in the SBM50 and SBM00 treatments were higher than of the control treatment (SBM100) because fresh golden apple snails with high moisture replaced soyabean meal. In order to make advantages for the ducks in the control treatment consuming the mash diets a small amount of fresh water was mixed with the mash before feeding to the ducks (Table 2).   

Experiment 2. Use of Tra fish by-products and golden apple snails as protein supplements in diets of crossbred meat ducks.

Experimental design

480 twenty-one day old ducklings were used for the experiment. The trial was carried out on a small farm in Omon district, Cantho City at the end of the rainy season in 2009. The ducks in the experiment were kept on plastic net floors with access to fish ponds for swimming and with biosecure controls, and were randomly allocated into four treatment groups, with three replicates. Each experimental unit (plot) consisted of 20 ducks, balanced for sex. The ducks were given four diets that contained 16% CP, but with different protein sources from SBM, Tra fish by-products (TF) and golden apple snails (GS). 

The experimental treatments were:  

CTL: rotein supplement only from SBM as a control diet

TF50:  A diet with TF replacing 50% of the protein of the SBM

TF100:   A diet with 100% replacement of the SBM by the TF

GS50:  A diet with GS replacing 50% of the protein of the SBM

 The ducks were given these diets ad-libitum up to 60 days of age.

 Diets and feeding

The chemical composition of the feedstuffs is shown in Table 3. The moisture content of golden apple snails was  highest  (78.3%) and then Tra fish by-products (56.9%). The protein content of the GS was  higher (54.9% in DM) than for TF (28.7%).

The crude protein content in all diets was kept constant at 16% based on 87% of DM (DM of the control treatment) .

Chemical analyses

The feeds were analysed for proximate constituents by AOAC methods (AOAC 2000). Metabolizable energy (ME) of the diets was calculated from chemical analysis data using the equation of Nehring and Haenlein (1973): ME (kcal/kg) = 4.26 X₁ + 9.5 X₂ + 4.23 X₃ + 4.08 X₄. The calculated digestable protein, digestible fat, digestible fibre and digestible nitrogen free extractives (g/kg of feed) are represented by X₁ through X₄, respectively. Estimated digestibility coefficients are according to NIAH (1992). The diets of the ducks in both experiments 1 and 2 were formulated by WinFeed software (2004).   

Statistical analyses

The data were analysed by analysis of variance using the ANOVA General Linear Model procedure of MINITAB (2003).

Economic analyses

Economic analyses were carried out using current prices in Vietnamese Dong (VND: 18,000 (2008) and 19,000 (2009) VND=1US$) to compare feed cost per unit live weight gain among the diet treatments.  

Results

Experiment 1: Evaluation of partial or complete replacements of golden apple snails for soyabean meal for feeding meat-type ducks

Growth rate and feed conversion were improved by replacing SBM with the golden apple snail (Table 6; Figure 1).

Figure 1: Daily weight gains of the ducks offered diets with or without GS

Carcass weights tended to be heavier on the GS diets. The thigh and breast muscle weights were much higher in the ducks fed diets with GS even after considering the increased carcass weights (Table 7).

The lowest feed costs per kg of live weight gain was for the SBM00 diet, in which the protein supplement was completely replaced by fresh golden apple snails (Table 8). There would thus appear to be marked economic benefits to the producers using golden apple snails gathered in the rice fields as a protein feed in diets of growing meat-type ducks.

Experiment 2: Evaluation of partial or complete replacement of soybean meal by Tra fish by-products and golden apple snails forcrossbred meat ducks

Daily total DM intakes of the ducks offered the CTL and GS50 diets were higher than those fed the TF50 or TF100 diets (Table 9), the lower intake on the latter reflecting the higher fat content of these diets. Weight gains were depressed with the highest level of TF but did not differ among the remaining diets (Figure 2). However, feed conversion showed the opposite trend with best conversion on the TF 100 diet.

Figure 2: Daily weight gains of the crossbred ducks supplemented with TF or GS

The data in Table 10 show that there were no differences for carcass yields, breast and thigh muscle proportions and leaf fat yields of the ducks offered the diets with or without Tra fish by-products or golden apple snails as protein supplements.  

The lowest feed cost per kg of live weight gain was with the TF00 diet, in which the protein supplement was completely replaced by fresh Tra fish by-products.

 Conclusions

• The ducks offered the diets with golden apple snail obtained daily weight gains, feed conversion ratios and breast and thigh muscle proportions, better than those with soybean meal.

•  Use of golden apple snail as a protein supplement to replace soybean meal decreased feed cost by 20 to 27%.

•  Tra fish by-product and golden apple snail can replace 50% of soybean meal in diets of growing crossbred meat ducks.

•  Use of Tra fish by-product and golden apple snail as a replacement for 50% of the protein from soybean meal in diets for growing crossbred meat ducks decreased the feed cost by 20-27%

References

AOAC 2000 Official methods of analysis. Association of Official Analytical Chemists, Washington, DC.

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Bui Xuan Men and Ogle R B 2003 Productivity and environmental and economic evaluation of integrated duck-rice-fish systems on smallholdings in the Mekong Delta of Vietnam. Proceedings National Workshop-Seminar “Sustainable Livestock Production on Local Feed Resources” Agricultural Publishing House. HCM city.

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