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Workshop-seminar "Making better  use of local feed resources" SAREC-UAF,  January , 2000

Evaluation of  ensiled shrimp by-products
 for fattening pigs

 

Nguyen Hoa Ly, Le Van An and Le Duc Ngoan

Hue University of Agriculture and Forestry, Hue City, Vietnam
upland@dng.vnn.vn

 

Abstract

An experiment was performed to evaluate different methods for shrimp by-product preservation and to determine its chemical composition. In addition two on-farm feeding trials were performed with growing pigs to evaluate the nutritive value of the ensiled shrimp by-products. In the first experiment three ratios of shrimp by-product (SBP) to cassava root meal (3:1, 2:1 and 1:1 wet weight of shrimp by-product and air-dry weight of cassava root meal) were investigated. The pH of the SBP ensiled with cassava root meal at a ratio of 1:1 decreased during the first week to below 4.5 and remained low up to day 56 of ensiling, whereas the pH of the mixtures with higher ratios of SBP remained above 7.0,  and the material deteriorated rapidly.

 

The first feeding trial was carried out on three farms with a total of eighteen F1 crossbred pigs (MongCai x LargeWhite) fed either the experimental diet with the protein supplied by shrimp by-product ensiled with molasses at a ratio of  3:1 (SBSMO), or a control diet with protein from groundnut cake. For the whole growing period (12 to 60 kg live weight) there were no significant differences between diets in daily live weight gain or feed conversion ratio: 348 and 321g/day, and 4.1 and 4.5, for the control and SBSMO diets, respectively. The second trial was conducted on three farms with sixteen F1 crossbred pigs (MC x LW) fed either an experimental diet with the protein supplied by shrimp by-product ensiled with cassava root meal (SBSCA) or a control diet with the protein from groundnut cake. There were no significant differences between diets. Weight gains were: 353 and 346g/day, and feed conversion 4.2 and 3.8 for the control and SBSCA diets, respectively.

 

Key words: shrimp by-product, silage, molasses, cassava root meal, fattening pigs, economics

 

Introduction

The main system of pig production in Central Vietnam is based on locally available feed resources produced on farm or in the villages. Rice bran, sweet potatoes, cassava, taro and vegetables are the main feeds. The protein content in the diet therefore is very low, and although groundnut cake is sometimes used as a protein source it is expensive and not available throughout the year.

 

In recent years shrimp production for export in Vietnam has increased rapidly, resulting in large quantities of by-product from the shrimp processing industry, estimated recently at around 42,000 tons annually (Nguyen Van Le et al 1995).  The by-product from shrimp processing consists of the head and shell, and is estimated to make up about fifty percent of the total raw material (Nguyen Van Le et al 1995; Balogun and Akegejo-Samsons 1992).

The traditional method to preserve shrimp by-product is salt-based ensiling. However, the high concentration of salt in the silage limits its use for feeding animals. Alternatively, shrimp by-product is preserved in the dry season by sun-drying to produce shrimp by-product meal, although as the shrimps are mainly harvested in the rainy season in Central Vietnam sun drying is difficult to apply as a preservation method.

 

Ensiling with carbohydrate-rich materials may be a more suitable method of preservation (Le Van Lien  et al 1994; Perez 1995). The advantage of silage-making is that this method does not depend on weather conditions, and that it usually produces a palatable feed. The main concern when making silage from shrimp by-product is that it has a high content of protein and a low carbohydrate content, thus making ensiling difficult unless readily fermentable carbohydrates are added. Cassava root meal, which is locally available throughout the year in Vietnam, is rich in carbohydrates and is therefore a potentially useful additive in silage making.

 

The objectives of these experiments were to determine the optimum ratio of shrimp by-product to cassava root meal for ensiling, and to evaluate this product, and shrimp by-product ensiled with molasses, in diets for fattening pigs under small-farm conditions in central Vietnam.

 

Materials and methods

On-station research

Ensiling of shrimp by-product

Shrimp by-products were supplied from the Seafood Processing Factory in Hue City in Central Vietnam. At the factory shrimps are processed by boiling in water prior to removing the head and the shell. These by-products were collected, ground to pass through a 5-mm screen, and mixed with different proportions of cassava root meal (CRM). The ratios of shrimp by-product to CRM were 3:1, 2:1 and 1:1 (wet weight of shrimp by-product and air-dry weight of cassava root meal). The mixtures were placed in 2 litre plastic bags, which were immediately sealed to prevent air contamination. The bags were put in buckets and stored at room temperature (20-30 ^ºC). The chemical composition of shrimp by-product and cassava root meal is shown in Table 1. The silages were ground carefully in a mixer and triple samples for dry matter (DM), pH, crude protein (CP) and ammonia-nitrogen (NH₃-N) determination were taken at day 0, 7, 14, 21, 28 and 56 after ensiling.

Chemical analysis

The chemical composition of the silage and  feed samples were determined using the following AOAC (1985) methods: Dry matter (DM) was measured by drying fresh samples at 100 ^ºC for 24 hours. Total nitrogen (N) was determined on fresh samples by the Kjeldahl method. Ether extract (EE) was determined by Soxhlet extraction without prior acid hydrolysis. Crude fibre (CF) was determined conventionally and acid detergent fibre (ADF) was determined according to Stelmock et al (1985). The ammonia nitrogen (NH₃-N) in the sample was determined by distillation with water and MgO, collection in 0.3 % H₃BO₃ and then titration with standard 0.1 N H₂SO₄. Total ash was the residue after ashing the samples at 550-600 ^ºC. The pH was determined in the liquid obtained by pressing fresh samples of the silage.

 

On-farm research

Animals

Thirty-four F1 crossbred pigs (Mong Cai x Large White) from 6 litters and of similar age and live weight were used. Five litters had 6 piglets and one litter had 4 piglets. All piglets were castrated and vaccinated and were adapted to the experimental feeds for 3 weeks before the start of the experiment. The pigs were kept by 6 families, and the farmers were trained to mix the diets and record data.

Experimental design

Experiment 1: Eighteen pigs with a live weight around 12 to 14 kg were randomly allocated to 3 families. Each farmer kept 6 pigs of the same litter, with 3 pigs per pen. One group of pigs on each farm was fed the experimental diet, which contained shrimp by-product ensiled with molasses (SBSMO) at a ratio of 3:1 (wet weight basis) while the second group was fed the control diet. The experiment lasted for 150 days.

Experiment 2: Sixteen pigs with a live weight around 15 to 18 kg were allocated to 3 families. Two farmers kept 6 pigs of the same litter, with 3 pigs per pen. One farmer kept 4 pigs, with 2 pigs per pen. One group of pigs on each farm was fed the experimental diet (SBSCA), while the second group was given the control diet. The experiment lasted 150 days.

Diets and feeding

    

The diets were composed of rice bran, cassava root meal, groundnut cake and ensiled shrimp by-product (Table 1). In addition, all pigs were fed fresh water spinach daily and had free access to fresh water. Shrimp by-product was bought from the factory within 5 hours after processing and was ground to a maximum size of 1 cm before mixing with the cassava root meal or molasses and ensiling.  The silage containers were opened from 3 weeks after ensiling and onwards, and the SBSCA and SBSMO mixed daily with the other feed ingredients before feeding.

Data collection

Pigs were weighed at the start of the experiment and on the 24^th day of every month during the experiment. They were weighed individually using a cage and a 50 or 100 kg scale. Feed consumption and feed costs were recorded daily by the farmers and the data collected by the researchers every week. Factors influencing the experiment, such as pig illness, environmental temperature, storms and flooding were recorded.

Statistical analysis

Data collected were analyzed by ANOVA using the General Linear Model (GLM) and regression analysis software of Minitab version 12 (1998). Results are presented as least squares means and their standard errors.

 

Results

On-station research

Effect of cassava root meal ratio on ensiled shrimp by-product

With ratios of shrimp by-product to cassava root meal of 3:1 and 2:1 the pH fell only slightly after 7 days, before increasing to its original value after 14 days.  NH₃-N concentrations increased rapidly, and the material had obviously spoiled after 14 days when measurements were discontinued (Table 2).

 

 

For treatment SBSCA 1:1, however, the pH fell to 4.2 after 7 days, and remained at this level up to 56 days. DM content fell after 14 days and then gradually increased to its original level after 56 days, while CP concentration increased after 21 days before falling back to its initial level after 56 days.

 

On-farm research

Pig performance

There were no differences between treatment (Table 3) for final weight, daily live weight gain  and feed conversion ratio (348 and 321g/day, and 4.1 and 4.5 kg feed/kg gain for the control and SBSMO diets, respectively). Similarly the between treatment differences in Trial 2 (Table 4) were small and non-significant. Daily gains and feed conversion values were: 353 and 346g/day and 3.8 and 4.2 kg feed/kg gain for the control and SBSCA diets, respectively.

 

 

 

Cost-benefit analysis of using ensiled shrimp by-products

The SBSCA diet was the least expensive at 2,324 VND/kg DM (Table 5), and the SBSMO diet was the most expensive, at 2,600 VND/kg DM (not including the labour costs of silage preparation). There were no significant differences in feed cost/kg weight gain between treatments.  However, this parameter was slightly lower on diet SBSCA than on the other diets. Using SBSCA reduced the costs by 13% compared to the control diet, while SBSMO increased the costs by 6% compared to the control.

 

 

Discussion

Effect of cassava root meal on ensiled shrimp by-product

Varying the proportions of shrimp by-product to cassava root meal in the silage markedly affected the preservation of the shrimp by-product. Hall and de Silva (1994) considered cassava root meal to be the best additive for silage making, as cassava stimulates lactic acid fermentation to produce a very low pH. This was not confirmed in the present study, as it should be noted that a very high proportion of cassava root meal to shrimp by-product (74:36 on a DM basis) was necessary to preserve the silage, probably due to the relatively low content of readily fermentable soluble starch in cassava root meal, compared with molasses.

 

 Growth performance of pigs fed shrimp by-product ensiled with molasses or cassava root meal

The shrimp by-product silage replaced 50 % of the total crude protein in treatment SBSMO and 70 % in treatment SBSCA, with an average crude protein content in the diets of 13%. There were no significant differences in performance between pigs fed a traditional diet with groundnut cake and the diets with ensiled shrimp by-products as protein sources. Husby (1980) found similar results when growing pigs were fed soyabean meal and crab meal protein diets, and suggested that crab meal could replace 50% of the protein provided by soyabean in barley-soyabean meal diets without any negative effect on pig performance. Perez (1995) reported that fish silage could replace 50 % of the protein from fish meal in pig diets without any negative effects on daily weight gain. In Vietnam, Lien and Thien (1994) studied the nutritional value of fermented shrimp heads and concluded that on a DM basis the shrimp head silage could replace 75 % of the fish meal.

 

Pig performance was rather poor in the present experiment, with growth rates of 320-350 g/day, and feed conversion of 3.8-4.5 kg feed/kg liveweight gain. However, these values are fairly typical for pig performance on small-holdings in central Vietnam, where crossbred local pigs normally attain a slaughter weight of 70 to 80 kg live weight in 10 to 12 months, with a FCR of 4.5 to 5.5 kg feed/kg LWG (Nguyen Thi Loc 1996). The low genetic potential of the local Vietnamese pigs makes them less sensitive to the feed protein quality. However, other studies with improved pigs have shown that high growth rates can be expected with both crab meal (Husby 1980) and fish silage. This indicates that shrimp by-product silage could replace groundnut cake and also other protein feeds as a protein source for feeding both local and improved pigs under farm conditions in Vietnam.

 

Cost-benefit analysis of using ensiled shrimp by-product for feeding pigs

The shrimp by-product ensiled with cassava root meal had the lowest costs measured as feed cost per kg dry matter and feed cost per kg LGW. The costs of using SBSMO were higher than using groundnut cake as a result of the high cost of molasses.

 

Conclusions

It is concluded that:

• Shrimp by-product can be successfully preserved for at least 8 weeks by ensiling with cassava root meal at a ratio of 1:1 (wet weight of shrimp by-product to air-dry weight of cassava root meal).
• The growth performance of pigs fed shrimp by-product ensiled with either molasses or cassava root meal was similar to those fed groundnut cake in traditional diets.
• The most cost-effective ensiling material was cassava root meal, while ensiling with molasses gave lower net benefits than feeding a traditional diet.
• Under practical conditions, shrimp by-product ensiled with cassava root meal can be an inexpensive and readily available protein supplement for pig diets in central Vietnam.

 

Acknowledgements

The study was financially supported by SAREC/SIDA and conducted in cooperation with the Swedish University of Agricultural Sciences and Hue University of Agriculture and Forestry. The authors would like to express their thanks to the farmers in Thuy Duong commune in Hue, who supported and made possible the feeding trials. We also appreciate the excellent  assistance of  Ms. Dao Thi Phuong and Mr. Nguyen Huu Bo.

 

References

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Balogun A M and Akegbejo-Samsons Y 1992  Waste yield, proximate and mineral composition of shrimp resources of Nigeria’s coastal waters. Bioresource Technology  40: 157-161

 

Hall G M and de Silva S 1994 Shrimp by-product ensilation. INFOFISH International 2:  27-30

 

Husby F M 1980  King Crab meal – a protein supplement for swine. Agroborealis 12(1): 4-8 

 

Le Van Lien,  Sansoucy R  and Nguyen Thien 1994  Preserving shrimp heads and animal blood with molasses and feeding them as a supplement for pigs. In:  Proceeding of the 1993 Sustainable Livestock Production on Local Feed Resources Workshop, Hanoi and  Ho Chi Minh City Vietnam pp 24-26

 

Minitab Version 12 1998  Minitab Inc PA USA

 

Nguyen Van Le,  Pham Thi Tran Chau , Nguyen Van Ngoan and Phan Thi Ha  1995

Chemical composition of shrimp by-product meal.  Journal of  Vietnam Fishery 4: 6-8 

 

Nguyen Thi Loc 1996 Evaluation of protein supplementation of traditional diets and cassava root silage for local crossbred pigs under village conditions in central Vietnam. MSc Thesis Swedish University of Agricultural Sciences Uppsala Sweden

 

Perez R  1995 Fish silage for feeding livestock. World Animal Review 82: 34-42

 

Stelmock R L  Husby  F M and Brundage A L 1985 Application of Van Soest’s

acid detergent fiber method for analysis of shellfish chitin. J  Dairy Sci 68: 1502-1506

 

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