Monitoring the nutritional value of feed components for aquaculture along the supply chain - an East African case study

R Nalwanga, D M Liti*, H Waidbacher**, J Munguti*** and W J Zollitsch****

National Fisheries Resources Research Institute(NaFIRRI), P.O Box 343, Jinja(Uganda)
* Moi University, Department of Biological Sciences, P.O Box 1125 Eldoret (Kenya)
** BOKU- University of Natural Resources and Applied Life Sciences Vienna, Department of Water, Atmosphere and Environment, 17 Max-Emanuel-Straße, A-1180 Vienna (Austria)
*** Kenya Marine & Fisheries Research Institute, Sangoro Aquaculture Station, P.O Box 136 PAP-Onditi Kisumu (Kenya)
**** BOKU- University of Natural Resources and Applied Life Sciences Vienna, Department of Sustainable Agricultural Systems, Division of Livestock Sciences, Gregor Mendel-Straße 33, A-1180 Vienna (Austria)
werner.zollitsch@boku.ac.at

Abstract

Constraints in the supply with high-quality feed constitute a main obstacle for the development of aquaculture in Sub-Saharan African countries. The nutritional quality both of commercially manufactured fish feed and of diets produced on-site by fish farmers, depend on the quality of feed ingredients used. This study was conducted in order to collect information about the nutrient content of selected feed components at different points of the supply chain. Additionally, the nutrient composition of commercial fish feeds was analyzed for a comparison with their labeled nutrient contents. For fish, fish meal, cottonseed cake, sunflower seed cake and maize bran samples were collected at landing sites, oil mills, milling sites, stores and shops in the Lake Victoria region of Uganda and Kenya, and were subjected to proximate analysis. The costs per unit of protein of feed ingredients were also estimated.

The results of the present study show that serious adulteration occurred between the primary outlet and the store or shop level. The main adulteration material most probably was sand. The deterioration of the nutritional value of feed ingredients coincides with the composition of the commercial fish feeds being substantially below the values labeled; this also affects the relative costs per unit of nutrient. It is recommended that whenever possible, ingredients should be purchased from landing sites and oil mills for fish (meal) and oilseed cakes, respectively, in order to get fairly accurately formulated feeds for fish farms. It should also be noted that the reduced feeding value is coinciding with increasing market prices along the supply chain, leading to a disproportionate increase in relative costs per unit of nutrient. It is therefore suggested that a set of measures should be developed to assure feed quality. Strategic sampling and regular feed analysis can be implemented immediately in order to improve the situation especially for small-scale fish producers who rely on purchased feed or feed ingredients.

Key words: Fish meal, fish production, protein, proximate analysis, quality control

Introduction

Aquaculture has a great potential in the struggle for improvement of the nutritional situation of the human population and in the alleviation of poverty of rural people especially in developing countries (Tacon 2001). At global level, aquaculture has grown tremendously from a production of less than 20 million tonnes in 1990 to a production of 60 million tonnes in 2004. However, in Sub-Saharan Africa, and even more so in Uganda, aquaculture has developed at a slower rate (FAO 2006). One of the major factors for the slower growth is the quality and price of manufactured fish feeds which producers usually rely on. As a response, efforts have been made to replace the expensive dietary protein from fish meal by cheaper plant protein sources and thereby support the production of inexpensive fish feeds (Gatlin III et al 2007; Liti et al 2006; Munguti et al 2006; Liti et al 2005; Mbahinzireki et al 2001; El-Sayed 1998).

Despite consulted efforts in developing suitable feeds and intensive evaluation of potential feed components, the impact of their processing and handling on nutritional quality and relative nutrient costs along the supply chain has largely been neglected. No reliable data are available about the nutritional value of both individual feed components and manufactured fish feed typically used in Eastern Africa. However, in the field there is anecdotal evidence of substantial differences between labelled and actual nutrient contents for fish feeds. Similar differences have been confirmed for feed for livestock which is also used in aquaculture in Eastern Africa (Liti et al 2005). Since the quality of complete feeds depends on the quality of ingredients (Glencross et al 2007; Li at al 2006; Aksnes and Mundheim 1997), the nutrient content of feed ingredients should be seen as a starting point for any attempt of improving feed quality at the production level.

Therefore the present study was conducted to evaluate the nutritional quality and cost implications of selected, relevant feed ingredients for fish feeds at outlets which are typically accessed by small-scale producers in the Lake Victoria region of Uganda and Kenya. Additionally, the nutrient composition of some relevant commercial fish feeds was also analyzed in order to compare it with their labelled nutrient contents.

Materials and methods 

Feed samples

For the present study, samples were collected of the major fish feed ingredients (fish meal, cottonseed cake, sunflower seed cake and maize bran) from different outlets. The outlets were categorized according to their position in the supply chain and included pimary outlets (i.e. landing sites at Lake Victoria, oil mills, grain factories), secondary outlets such as milling plants where only grinding takes place and final outlets such as stores and shops in the Lake Victoria region (Table 1). Additionally, samples of formulated commercial feeds frequently used in the Lake Victoria region of Uganda were also collected from feed mills, dealers and farmers. Costs per kilogram of feed (component) were recorded in interviews at the respective level. Information about nutritional quality given on feed labels was also considered.

All samples were sun dried for three days before they were crushed. Two-hundred grams of each sample were ground into fine particles using an electric grinder fitted with a 1 mm sieve (Thomas-Wiley intermediate mill, 3348-L10 series, USA). The ground samples were stored in sampling bottles until proximate analysis was performed in the laboratory of Sagana Aquaculture Centre of the Ministry of Fisheries Development – Fisheries Department, Kenya.

Chemical analysis

Analyses of crude protein, crude fibre, ether extracts, ash and moisture were done in triplicates, generally following AOAC (1995) procedures. Dry matter (DM) was determined by drying 5 g of sample to constant weight in an oven at 103°C. Ash was then determined by ashing the 5 g at 550°C in a muffle furnace for 4 ½ hours. Crude protein (CP) was quantified by the standard micro-Kjeldahl method, using a sample size of 0.4 g. Ammonia was distilled into 70 ml of 4 % boric acid solution, prior to titration with 0.1 M HCl. A factor of 6.25 was used to convert Nitrogen to CP. Crude fibre (CF) was determined by boiling 0.5 g of sample (1.0 g in the case of samples with an expectedly low fibre content such as fish meal) in a solution of 3.13 % H₂SO₄ for 10 minutes. The remaining sample was then rinsed repeatedly with hot water, followed by acetone to remove fats. The sample was then boiled in 1.25 % NaOH for another 10 minutes and afterwards repeatedly rinsed with hot distilled water. The residue was oven dried at 103°C for 24 hours, cooled in a desiccator and weighed. The residue was ashed at 550°C in a muffle furnace for 4 ½ hours. CF was quantified by expressing the loss in weight after ashing as a percentage of the original weight of the sample. Ether extracts (EE) were gravimetrically analyzed using a sample size of 2 g in a Soxhlet extractor with petroleum ether (boiling point 40-60°C). N-free extracts (NfE) were estimated by difference of (DM-CP-EE-CF-Ash).

Calculations

Costs per unit of CP were calculated based on cost per kilogram of ingredient or feed from different sources (with an assumed exchange rate of 1 US$=1,717.8 Uganda Shillings) and results from proximate analysis.

Statistical analysis

All data were subjected to one-way analysis of variance (ANOVA) using SPSS software (SPSS 2004). All data given in percent were transformed (arcsin√(p/100)) prior to statistical analysis. Variance homogeneity and data normality were tested by Levene test and Kolmogorov-Smirnov and Shapiro-Wilk, respectively. Bonferroni multiple range test and t-test were used to compare differences among individual means (Kraps and Lamberson 2004). Treatment effects were considered to be significant at p<0.05.

Results 

In the following sections, the results are presented for nutrient contents of single feed ingredients sampled at different outlets, for manufactured complete fish feeds and for the cost implications along the supply chain. The latter includes the relationship between market price and reduction in nutritional value as indicated by CP content.

Nutrient contents of feed ingredients

Results from proximate analysis of fish and fish meal showed that the contents of CP and EE decreased significantly from landing sites to stores and shops, while CF, NfE and especially ash increased tremendously from landing sites to stores and shops (p<0.05; Figure 1).

Fish from landing sites showed the significantly highest protein levels of 66 % on average. In stores, there was a significant decrease in the protein and lipid levels while ash, CF and NfE showed an increase as compared to fish from the landing sites (p<0.05). This trend continued from the store to the shop level (Figure 1). Variability as described by the standard deviation was also greater for protein and ash contents of fish meal from shops (±4.39 % and ±7.12 %, respectively) as compared to fish from landing sites (1.55 % and ±.4.14 %, respectively).

Like fish meal, the nutritional quality of cottonseed cake significantly decreased from oil mills to shops (Figure 2). Contents of CP, CF, EE and NfE showed a decreasing trend from oil mills to shops while ash levels showed a dramatic increase (p<0.05) along the chain of distribution.

Samples from oil mills on average had a significantly higher CP content (31.4±4.61 %) than cottonseed cake collected at milling plants where grinding took place (27.9±2.97 %) and stores (26.8±0.31 %), while samples from shops had the lowest CP content (22.4 ±1.91 %; p<0.05). In terms of ash, there was a tremendous increase from oil mills to shops (6.0±1.23 % vs. 32.7±2.59 % vs. 43.4±1.61 % for oil mills, stores and shops, respectively). CF levels significantly decreased from 17.1±5.23 % in oil mills to 10.4±2.81 % and 11.5±7.60 % in stores and shops, respectively. Overall, cottonseed cake purchased from shops had the lowest nutritional value, as characterised by low protein and highest ash contents, the best nutritional quality in terms of CP and lipid content was found for samples from oil mills.

A similar trend was observed for sunflower seed cake, which also significantly decreased in its nutritional quality throughout the chain of distribution: CP, and EE, but also CF showed a decreasing trend from oil mills to shops, while the opposite was true for ash and NfE (for the latter, this only applies up to the store level; Figure 3).

Unground sunflower seed cake from oil mills and milling plants showed significantly higher protein levels (25.1±2.51 % and 25.5±2.05 %, respectively) as compared to stores and shops (22.3±1.55 % and 16.8±1.62 %, respectively). Samples collected at stores showed a higher CP content than those sampled from shops (p<0.05). CF levels significantly decreased from oil mills and milling plants (31.6±6.40 % and 27.1±9.48 %, respectively) to stores and shops (17.6±7.07 % and 11.8±2.43 %, respectively), while ash levels increased from 4.7±0.23 % for samples from oil mills to 38.4±22.81 % for samples collected in shops (p<0.05).

Unlike fish, fish meal and oilseed cakes, maize bran did not show such distinct differences in its nutritional value along the chain of distribution (Table 2)

On average, maize bran from grain mills showed a protein content of 12.8±0.51 % which was significantly different from that of samples from stores (15.3±0.21 %), but similar to values found on shop level (13.8±1.65 %). Overall, only minor differences could be found for the proximate composition of maize bran from different outlets.

Nutrient contents of manufactured complete feeds

In order to get preliminary information about whether the differences in the nutrient contents of single feed components as described may also be reflected in the nutritional quality of commercial complete fish feeds, samples have been collected from feeds which are commonly available in the Lake Victoria region of Uganda, including a mixed feed produced in Kenya (Table 3).

Only for the pelleted fry feed which is a product imported from the USA and for the pelleted Grower 3 from Kenya, the analysed CP content matched and even exceeded the CP content that was labelled. These two feeds also clearly differed from the other ones in their ash content. Among the other feedstuffs analysed, only Grower 1 had a CP content that came close to the labelled value.

Large differences were observed for the relative costs of protein of the feedstuffs analysed. Based on this trait, the feedstuffs can be roughly differentiated into 3 classes: the Fry feed clearly provides the most costly protein, protein from both starter feeds plus Grower 1 and 2 costs between 1.1 and 1.6 US $ per kg, while the Grower 3 represents the most inexpensive source of protein.

Cost implications along the supply chain

The costs per unit of protein significantly increased along the supply chain for all feed components (Figure 4).

The costs per kilogram of fish protein in shops is three times that in landing sites, while costs per kilogram of protein from oilseed cakes in shops is double that in oil mills. The shops are the most expensive outlets, followed by stores, while the best cost-efficiency is found for landing sites and oil mills, respectively.

Discussion 

The results presented herein revealed that the nutritional quality of the investigated ingredients varied from source to source. There was a significant decline especially in protein content of the ingredients from primary outlets to outlets positioned downstream the supply chain: ingredients from landing sites and oil mills had a better nutritional quality than ingredients from stores and shops. These changes in nutritional quality were most probably due to deliberate adulteration. Most likely, the predominant adulteration materials were of inorganic origin, as supported by an increase in ash (Figures 1 to 3).

The nutritional quality of fish meal and the oilseed cakes was highest in primary outlets, i.e. landing sites and oil mills, respectively, which indicates that the contamination happened somewhere further downstream the supply chain. The CP content of fish from landing sites reported here are in the range of values reported for similar material from Lake Victoria, but the lipid content did not reach the respective level (Oduho et al 2005). Stores sold fish meal of significantly inferior quality as compared to fish from landing sites. Fish meal from stores had lower protein levels and substantially higher ash levels (Figure 1). These results and information collected during interviews with the ingredient dealers suggest an adulteration of fish meal by adding inorganic materials such as shells of young Pila ovata and sand to increase weight. The already relatively high ash content of samples from the landing sites is probably due to an inadvertent contamination with sand of fish put on the ground for sun drying (Oduho et al 2005; Sablani et al 2002). Certain characteristics of screened ash of fish meal also supported the hypothesis that sand had been added: fish meal from stores and shops had higher fractions of large grains of sand than fish sampled at landing sites. The colour of fish meal ash also varied from landing site through stores to shops: samples from landing sites had gray ash of lower particle size, while the fish meal from stores and shops showed brown, coarse ash. It should be noted that the quality of fish meal further decreased from stores to shops. Although not as distinct as for ash, the elevated CF content of samples from stores and even more from shops point to a possible contamination with fibrous material. According to information from interview partners, cottonseed cake, roasted maize bran and sometimes goat faeces may have been added to fish meal.

The nutritional quality of cottonseed cake correlates with its physical form. In milling plants, the ground cottonseed cake had a lower nutritional quality than the unground cottonseed cake even from the same source (Figure 2). The observed difference in nutritional quality was probably due to the mixing of cottonseed cake of different nutritional qualities after grinding. Dealers gave evidence of mixing of expensive, high quality cottonseed cake from Tanzania oil mills with the cheaper, fibrous cottonseed cake from Uganda and Kenya oil mills. The mixture is then sold at the higher price of pure Tanzania-cottonseed cake to increase profit. This was especially seen at two milling plants, where the unground products had higher CP and lower CF levels than the ground products from the same plants.

Not only physical form, but also handling influences the nutritional quality of cottonseed cake: samples from stores and shops had a lower nutritional quality as compared to those collected at oil mills and milling plants. This was probably due to the addition of both inorganic and organic materials. In interviews with store and shop keepers, the addition of materials such as sand and roasted maize bran was mentioned. The high levels of ash may confirm the addition of sand, while the low levels of CF in cottonseed cake from shops indicate the addition of roasted maize bran. Maize bran contains lower levels of CF as compared to cottonseed cake (Munguti et al 2006). However, the relatively high levels of CP in relation to ash levels in stores and shops may suggest the addition of nitrogen containing materials such as animal wastes. For example, in shops CP levels were on average 22 % as compared to 28 % and 31 % in stores and milling plants, respectively. Ash levels on average were 43 % in shops and at such high levels of ash one could expect lower CP contents.

Like fish (meal) and cottonseed cake, the nutritional quality of sunflower seed cake is also influenced by handling. Similar to cottonseed cake, samples from oil mills and milling plants were of higher nutritional quality than those from stores and shops. The dramatically high levels of ash in sunflower seed cake from shops suggest the addition of inorganic materials (sand). Information collected in interviews with dealers also supports the deliberate addition of sand to samples from stores and shops.

Unlike fish (meal) and oil cakes, maize bran from factories, stores and shops had almost identical nutritional quality. The apparent lack of manipulation of the nutritive value is on the one hand probably due to its low market price (Figure 5). Relating the relative loss in protein of feed components observed along the supply chain to the average market price of feed components results in a significant (p<0.05) positive correlation of 0.98: the higher the price of an ingredient, the higher the change in protein content along the chain of distribution. On the other hand, cereal brans usually are not further processed after milling and separation, which also prevents them from contamination and undeliberate adulteration.

Cost implications

Despite the decreasing nutritional quality of feed ingredients, the cost per kilogram of an ingredient increases between different outlets. This results in disproportionately increasing costs per unit of nutrient along the chain of distribution. For feed components of both animal and plant origin, the costs per unit of protein is highest in shops and lowest in landing sites, oil and grain mills (Figure 4). These price differences and the quantitatively or temporarily limited availability of certain high-quality feed components provoked many studies on the replacement of fish meal by plant protein sources (Gatlin III et al 2007; Gaber 2006; Liti et al 2006; Mugunti et al 2006; Ng et al 2006; Mbahinzireki et al 2001; El-Saidy 1999). Despite their high price, animal protein sources such as fish meals may possess specific benefits, such as high acceptability, good digestibility, well balanced amino acid profiles and a high content of polyunsaturated fatty acids (Gatlin III et al 2007; Lin and Shiau 2007; Li et al 2006; Miles and Chapman 2006; El-Sayed 2004; Hardy and Barrows 2002; Watanabe 2002; Jauncey 1998). However, in this study, cottonseed cake was more cost effective than sunflower seed cake in terms of costs per kg of CP, especially at the store and shop level (Figure 4).

Nevertheless it must be kept in mind that the replacement of fish meal by plant protein sources may result in reduced specific weight gain and increased feed conversion ratios due to impaired protein quality of the diet. However, this may vary with the fish species under culture. Therefore and despite the fact that animal protein sources are more costly than plant protein sources, ingredients of animal origin and especially fish meal may be essential for rapid fish growth and high yields (Jose et al 2006).

In Uganda, feed millers reported to purchase most of their ingredients from landing sites and factories. However, the majority of fish producers are still small-scale farmers who make feeds on their farms. For them, knowing sources of ingredients with reliable nutritional composition at a reasonable price is a prerequisite for their economic success.

Commercial feeds

Except one, all locally produced commercial feeds had lower than the advertised protein levels. The nutritional quality and cost of fish feeds largely depend on protein-rich ingredients, especially fish meal (Jose et al 2006; Miles and Chapman 2007). The great differences in the nutritional quality of certain ingredients purchased at different outlets are probably one of the contributing factors for not meeting the target protein levels in locally formulated feeds. Because of the lack of information about the nutritive value of feedstuffs used in the field, farmers obviously buy very expensive feeds of inferior quality. A similar problem will occur for commercial feed producers who use data from feed tables rather than from chemical analysis of their feed components as the basis of feed formulation. For example, the two starter feeds had similar or even lower protein contents as compared to the grower feeds (Table 3) and are therefore not sufficient to cover the high protein requirement of fingerlings (Lim and Webster 2006; Jauncey 2000). The results for commercial feeds presented herein are in agreement with Liti et al (2005) who found lower than labelled protein contents of commercial pig and poultry feeds used for feeding tilapia. This is likely to result in poor fish yields and high costs and may even constitute a factor hampering the development of local aquaculture.

Concerning the cost per unit of protein of the two starter feeds present on the market in Uganda (Table 3), Starter 2 is less costly than Starter 1. However, it should be noted that Starter 2 is in a mashed form, while Starter 1 is pelleted, which may actually influence fish growth rates. Pelleting improves feed utilisation and hence growth rates (Chu 2000; Jurgens 1997; NRC 1993). Additionally, the decreased feed waste associated with pelleted diets further reduces environmental problems associated with high nutrient loads. A study published by Chu (2000) on the relationship between physical structure of feed and feed loss showed less feed wastage with pelleted feeds than with mash feed. However, Jurgens (1997) reported that pelleting increases the cost of the feed by 3 to 5 US $ per metric ton of feed and this is reflected in market prices. Thus pelleting contributes to the price differences presented in Table 3. The imported fry feed (Table 3) met the target crude protein level of 44%. Nevertheless it should be noted that its price on the local market (3.71 US$ per kilogram) is so high that the majority of farmers cannot afford it.

Poor quality feed ingredients not only affect the economic returns for farmers through poor fish yields, but also cause problems in feed manufacturing: high sand levels may cause substantial wearing of technical equipment, especially the pelleting units. A case of serious problems due to wearing of the pelleting dies and rollers because of the use of sandy ingredients was reported from Zambia (Jauncey 1998).

Conclusions 

• The nutritional value of important ingredients for fish diets is likely to be substantially different between different outlets in the supply chains for the Lake Victoria regions of Kenya and Uganda. The magnitude of the differences and the likely causality point to deliberate adulteration, which mainly occurred between the primary outlets and the level of stores and shops. The degree of adulteration is correlated with the market price of components. Fish meal and oilseed cakes are specifically affected, with sand and certain organic materials being the main contaminants. Thereby not only the nutrient content of single feed components is significantly lowered, but also the nutritional value of locally formulated fish feeds is likely to be deteriorated, as could be shown herein for some selected feeds.

  
  

• Therefore quality assurance schemes should be developed in order to improve the situation described herein. As one element of such a scheme, some kind of quality control of feed ingredients is needed at all outlet levels in order to secure the production of fish feeds of sufficient quality. Thereof, regular feed analysis on the basis of strategic sampling should be implemented immediately. Specific attention should be given to outlets at the downstream part of the supply chain. Among the great number of feed components, fish meal should be given a high priority in quality control schemes as it is the most costly and most important component for balancing supply and requirement for essential nutrients. While the development of a suitable quality assurance scheme will be important for all fish producers and the related feed industry, small-scale fish producers will most strongly depend on such a set of measures, as they usually lack the opportunity to implement sophisticated quality control measures.
   

Acknowledgements 

The authors thank the Austrian Academy of Sciences and the Netherlands Fellowship programme (NFP) for funding. Special thanks are expressed to the IPGL programme co-ordinator G. Winkler and his team. The authors gratefully acknowledge additional funding from the European Community via the EU-FP6-BOMOSA project (INCO-CT-2006-032103). The authors also take the opportunity to thank the partners of the BOMOSA project for providing laboratory infrastructure at Sagana Aquaculture Centre. S.J. Balirwa and L. Ndawula (NaFIRRI) as well as F.W.B. Bugenyi (Makerere University) are acknowledged for their support.

Disclaimer 

The views expressed in this publication are the sole responsibility of the authors and do not necessarily reflect the views of the European Commission. Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of the information contained herein.

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Received 2 April 2009; Accepted 24 June 2009; Published 1 September 2009

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