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Metabolizable Energy in Different Shea Nut (Vitellaria paradoxa) Meal Samples for Broiler Chickens¹

H. K. Dei^*,2, S. P. Rose^*, A. M. Mackenzie^* and V. Pirgozliev

^* The National Institute of Poultry Husbandry, Harper Adams University College, Newport, Shropshire TF10 8NB, United Kingdom; and Scottish Agricultural College, ASRC, Ayr, KA6 5HW, United Kingdom

² Corresponding author: hdei{at}harper-adams.ac.uk

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Shea nut meal is obtained after fat extraction from shea nuts produced in West Africa. Two experiments compared the ME of different shea nut meal samples. The objective of the first experiment was to estimate the TME_n of 2 expeller shea nut meal samples and a single nonindustrial shea nut meal sample using a precision-fed broiler assay. The second objective was to compare the nutrient composition of 6 collected shea nut meal samples (i.e., 4 expeller, 2 nonindustrial) as well as 2 defatted samples (1 expeller, 1 nonindustrial) and to examine the differences in AME between the samples. The 8 shea nut meal samples were fed at 3 dietary levels (0, 2, 4%) in a nutritionally complete basal diet to 180 Ross male broiler chicks (12 to 20 d) in an AME assay. The mean TME_n (3,577 kcal/kg of DM) of expeller samples was higher (P < 0.001) than TME_n (3,017 kcal/kg of DM) of the nonindustrial sample. The dietary level of shea nut meal had a significant (P < 0.01) effect on AME with the 4% level tending to give a lower AME than the 0 or 2% levels. However, increasing levels of defatted shea nut meals from 2 to 4% had no effect on AME of the diets. It was concluded that the available energy concentrations in the shea nut meal samples were low relative to their nutrient compositions and variable due to the content and nature of the residual fat. The variation observed among samples indicates that industrial expeller shea nut meal samples are preferable to nonindustrial meals for use in poultry rations. The nutritional quality of shea nut meal still needs improvement to allow it to be a valuable feed ingredient.

Key Words: shea nut meal • metabolizable energy • broiler

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
The shea tree (Vitellaria paradoxa, Gaertn.) grows in West Africa, and the nuts are harvested primarily for their fat content. Increasing world demand for shea fat as a cocoa butter substitute, as well as for cosmetics (Hall et al., 1996) has increased the supply of shea nut meal in sub-Saharan Africa. Shea nut meal is the residue that remains after fat extraction from the harvested nuts, and fat extraction from shea nuts is either conducted by a nonindustrial water-based method or industrial mechanized processes (e.g., screw-press). There is a paucity of information on the potential of shea nut meal for use in poultry feeds. Some studies have been conducted on broiler growth performance (Annongu et al., 1996; Atuahene et al., 1998; Olorede et al., 1999). However, there is a lack of information on the dietary energy availability of the meal. There are variable fat extraction efficiencies in the industry (Womeni et al., 2002) that could cause large variations in the gross energies of different products. The utilization of shea fat by poultry is poor because it is highly saturated (Dei et al., 2006) and may frequently have high free fatty acid content.

The first objective of this study was to compare the TME_n of 2 expeller shea nut meal samples and a single nonindustrial shea nut meal using a rapid TME chicken assay. The second objective was to determine the effects of 6 shea nut meal samples (4 expeller meals from 2 different factories and 2 nonindustrial meals) and 2 defatted samples (1 expeller and 1 nonindustrial) on dietary AME at 3 inclusion levels (0, 2, and 4%) by using an AME broiler assay.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Shea Nut Meal Samples

Six shea nut meal samples were obtained from Ghana for the study. Four of the shea nut meal samples were produced by the same industrial process (expeller fat extraction), but by different factories [Shebu-Loders Croklaan Ltd., Savelugu, Ghana (3 samples) and Juaben Oilmills, Juaben, Ghana (1 sample)]. The industrial expeller shea nut meal process involved steaming (wet heating) the kernels before fat extraction using a screw-press. Two additional shea nut meal samples were obtained from a local, nonindustrial (water-based fat extraction) processor (Christian Mothers Association, Tamale, Ghana). This material was produced by a traditional method of roasting the kernels, grinding in a mill prior to water-based fat extraction using hand kneading, scooping off the fat emulsion, and sun-drying the residue. Three of the 6 shea nut meal samples were produced during the 2004 growing season and the other 3 in 2005. All the samples obtained were stored at ambient temperatures at source (approximately 25°C) and, after transport, in cold storage at 4°C (UK).

Two additional shea nut meal samples were prepared by removing the residual fat from 2 of the shea nut meals collected (1 expeller meal and 1 nonindustrial meal from the 2004 season). The fat in the shea nut meal was removed through continuous extraction with petroleum ether (boiling point 40 to 60°C) using a Soxtec system (Foss Ltd., Didcot, UK).

True Metabolizable Energy Broiler Assay

Three shea nut meals [2 expeller meals (2004 and 2005) from the Shebu-Loders Croklaan Ltd. and 1 nonindustrial meal (2004)] were used for this experiment. Each shea nut meal was fed to 1 of 8 Ross 308 male broilers in a randomized block design according to an adapted precision feeding technique to determine TME_n (McNab and Blair, 1988). This modified TME bioassay improves the TME method originally devised by Sibbald (1976) by extending the excreta collection time from 24 to 48 h as well as feeding dextrose before and once during the collection period to decrease the stress on the birds used for the determination of endogenous losses. The experiment was conducted at the Scottish Agricultural College, Auchincruive, UK, and was approved by the Scottish Agricultural College Animal Ethics Committee. All experimental birds were previously fed the same commercial diet. At 45 d of age, the birds were placed on a raised slatted floor pen with no access to feed, litter, or droppings. Water was supplied ad libitum throughout the study via a suspended nipple drinker line. After 24 h the birds were given 50 mL of 60% glucose solution. After a further 24 h, each bird was fed 30 g of the test samples and placed in individual cages (0.5 m x 0.8 m floor area) designed to collect excreta, at a constant house temperature of 20°C and 23 h of light per day. Birds used for endogenous loss estimation were fed 50-mL glucose solution instead of the experimental diets. The excreta voided by each bird were collected for 48 h, frozen, and freeze-dried.

AME Broiler Assay

This experiment was conducted at the National Institute for Poultry Husbandry, Harper Adams University College and was approved by the Animal Ethics Committee, Harper Adams University College, UK. Ross 308 male broiler chicks were reared in a solid-floored pen and fed a crumbled-pellet broiler starter diet (CP = 23.5%, ME = 3,026 kcal/kg) for 12 d. At 12 d of age, 180 broilers of similar body weight were individually caged (0.3 m x 0.3 m x 0.36 m) and fed 1 of 17 mash experimental diets to 20 d of age. The basal diet (Table 1) was diluted with shea nut meal at 0, 2, and 4%. The calculated nutrients in the basal diet met NRC (1994) specifications for broilers, except ME that was low by 300 kcal/kg. During the 8-d experiment, the feed offered during the last 4 d was restricted to an amount estimated to be 70% of ad libitum feed intake of the control diet based on ad libitum feed intake (recorded the previous day) of birds kept for that purpose. This was done to avoid any confounding of lower feed intakes due to the presence of dietary shea nut meal. Shea nut meal contains relatively high levels of tannins (i.e., comparable with that of sorghum) so some reduction of voluntary feed intakes would be expected. The excreta were collected daily and stored at 4°C until the combined 4-d sample was then immediately dried in a forced-draught oven at 60°C.

The shea nut meal samples were ground in a laboratory mill fitted with a 1-mm mesh screen. Dry matter content of the samples was determined by drying the samples in an oven at 100°C. The nitrogen content of the samples was determined by the combustion method (AOAC, 2000) using Leco (FP-528 N; Leco Corp., St. Joseph, MI) with EDTA as a standard. The crude protein content of the samples was calculated from its nitrogen composition (N x 6.25). The gross energy content of samples was determined by adiabatic bomb calorimeter (model 1261; Parr Instrument Co., Moline, IL) with Analar sucrose used as a standard. Crude fat content of samples was determined by the ether extraction method (AOAC, 2000) using a Soxtec system (Foss UK Ltd.) following digestion by hydrochloric acid (4 M) using the wet digestion method (AOAC, 2000). The free fatty acid content of the fat extracted from the samples was determined by the titration method (AOAC, 2000) and expressed as percent oleic acid. The ash content of samples was determined by combustion in a muffle furnace for 24 h at 500°C. Calcium and phosphorus contents of the samples were determined using atomic absorption spectrophotometry (Smith-Hieftje 1000; Thermo Electron Corp., Hampstead, UK) and standard wavelength spectrophotometry (DU 640; Beckman, Fullerton, CA), respectively. The measurements of total, soluble and insoluble nonstarch polysaccharides on fat-free samples (AOAC, 2000) were carried out according to procedures outlined in the Megazyme nonstarch polysaccharides assay kit (Megazyme International Ireland Ltd., Bray, County Wicklow). The excreta samples were analyzed for their contents of dry matter, nitrogen, and GE as described earlier. Each chemical component of the samples was determined in duplicate.

The amino acids in the samples were determined at the Animal Nutrition Division of Degussa Ltd. (Hanau, Germany) using an HPLC (Biochrom 20; Amersham Pharmacia Biotech, Cambridge, UK). The AOAC (2000) methods were used that involved oxidation of the protein with performic acid followed by acid hydrolysis. Tryptophan was determined following alkaline hydrolysis in an autoclave.

Total extractable tannins were determined at the Wildlife Habitat/Nutrition Laboratory of the Department of Natural Resource Sciences, Washington State University, Pullman, according to the procedure of Martin and Martin (1982) using the BSA binding assay. The results were obtained as tannin binding capacity in milligrams of BSA precipitate per gram of sample. Both proanthocyanidins and hydrolysable tannins in the samples were determined at the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, Olsztyn, Poland. The proanthocyanidins were determined by the acid-butanol reagent method of Porter et al. (1986) as cyanidins using DU 7500 (Beckman) and detected at a 550 nm wavelength. Hydrolysable tannins were determined as gallic acid after enzymatic hydrolysis by tannase according to the procedure of Karama et al. (2006) using a Shimadzu HPLC system (Shimadzu Corp., Kyoto, Japan) and detected at a 280 nm wavelength. The saponin in the samples was determined at the Institute of Agricultural Research and Training, Ibadan, Nigeria) by the method of Wall et al. (1952). The sample was extracted with ethanol in a soxhlet apparatus, and the extract was defatted with benzene in a continuous liquid-liquid extractor. The addition of butanol formed a butanol-saponin extract that was quantified using rat red blood cells.

Calculations

The AME value of the diet was calculated from the GE values of the diet and excreta using the formula

The TME_n contents of the shea nut meal samples were calculated based on equations of Sibbald (1976) as follows: TME = [(EI – EO)/FI] + (FEL/FI), TME_n = TME – (8.22 x ANR/FI) – (8.22 x FNL/FI); where EI is gross energy intake (kcal), EO is gross energy output (kcal), FI is the feed intake of the feedstuffs (30 g), ANR is apparent nitrogen retention (g), FEL is fasting energy loss (kcal) from the feed deprived birds, and FNL is fasting N loss (g). Nitrogen retained in tissues can be catabolized to yield energy-containing excretory compounds that contribute to fasting energy loss. Therefore, the gross energy excreted was corrected to zero-N balance using a factor of 8.22 kcal/g (Hill and Anderson, 1958).

Data and Statistical Analysis

Source of shea nut meal was considered the treatment factor for the TME_n broiler assay, whereas source and level were considered as treatment factors with tier level of cages as a blocking factor for the AME broiler assay. In both assays, outliers that were greater than 3 standard deviations from the treatment means were removed from the data sets for all variables. The ANOVA of data and orthogonal contrasts were used to compare the treatment means [GENSTAT (Lawes Agricultural Trust, 2005)]. The relationship between the determined AME of the samples and their chemical composition was examined by linear regression within groups (industrial or nonindustrial meals) techniques.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
There were variations in the fat content, free fatty acids, and tannins of shea nut meal samples produced by the 2 different processing methods (Table 2). The nonindustrially produced meals had a higher fat content than the industrially produced expeller meals. This could be due to the different efficiencies of fat extraction methods within the industry (Womeni et al., 2002) that are particularly more efficient for the expeller method compared with the water-based, nonindustrial method. Also, the operational efficiency of the expeller process could influence the level of residual fat of the meal and explain the variation in fat of the 4 expeller meal samples that were used in this study. The nonindustrial meals had a much greater proportion of free fatty acids (FFA) than the expeller meals. The FFA content of the total fat tended to be higher in the 2004 than the 2005 samples. The variation observed in the FFA content of the fat could either be due to a seasonal effect on kernels, harvesting, and nut preparation methods (Hall et al., 1996) or poor storage conditions at source after fat extraction due to oxidation.

Removal of the residual fat in the 2 different shea nut meal samples reduced the saponin contents of the samples (Table 2). The unsaponifiable material in unrefined shea fat (e.g., sterols) is high relative to other vegetable oils (Padley et al., 1994). Therefore, processing methods that substantially improve fat extraction efficiency (for example solvent extraction processes) from the shea kernels may enhance the quality of this by-product for feeding poultry.

Although the nonindustrial shea nut meal had a high fat content (Table 2), it had a lower (P < 0.001) TME_n than the expeller meals (Table 3). However, both expeller meals had similar TME_n. The TME_n of the nonindustrial nut meal was 560 kcal/kg lower than the mean values of the expeller meals. The nonindustrial meal’s high residual fat content as well as high concentration of FFA of the fat (Table 2) might have accounted for its lower energy availability. Shea fat consists of stearic (43.0%), palmitic (3.6%), arachidic (1.5%), pentadecanoic (0.2%), oleic (44.9%), linoleic (6.4%), and erucic (0.4%) acids and has a low unsaturated-to-saturated fatty acid ratio (1.1). Thus it is highly saturated and has relatively low ME content (Dei et al., 2006). Triglycerides with low unsaturated-to-saturated fatty acid ratios have been shown to have lower ME concentrations (Ketels and De Groote, 1989), particularly at high dietary concentrations (Wiseman et al., 1986). Also, there is a negative relationship between the FFA level of a fat and its ME (Huyghebaert et al., 1988; Wiseman and Salvador, 1991). In the TME assay, shea nut meal was the sole feed. Therefore, the relatively high fat content of the samples could have markedly reduced the estimate of ME because not only did the meals have a high dietary concentration of saturated fats but also had high FFA concentrations. The high nonstarch polysaccharides in the shea nut meals (Table 2) could be another cause of their relatively low energy availability. Morgan and Trinder (1980) used an in vitro study and found a low digestible organic matter and total digestible nutrients in a shea nut meal sample that they attributed to the fiber content of the meal. It is also possible that the high tannin contents of the meals could have had a pronounced negative effect on ME (Smulikowska et al., 2001).

Addition of the 8 shea nut meal samples to the balanced diets showed there was an interaction between the source and level on AME. The dietary level of the 6 original, as-received shea nut meal samples had a significant (P < 0.01) effect on AME with the 4% level giving a lower AME than the 2% level (Table 4). However, this effect was not evident for the 2 defatted samples. Increasing dietary inclusion levels from 2 to 4% of these 2 samples had no effect on AME of the diets (Table 4). Even though the AME of refined shea fat is approximately 5,263 kcal/kg (Dei et al., 2006), there was no relationship between the level of residual fat in the shea nut meal and AME. However, the lack of relationship between total fat level and AME suggests that another quality factor may also have been important. All the shea nut meal samples had residual fats with relatively high FFA contents, and in particular, the nonindustrial samples had very high FFA levels. This indicates that the residual fat in the shea nut meal may not contribute significantly to its ME content as expected. The defatted shea nut meals had high metabolizability (AME/GE; mean of 0.842) compared with the other 6 shea nut meal samples (mean of 0.526). This gives further evidence that the fat content of shea nut meal may have a deleterious effect on ME although the defatting process also reduced the saponin concentration by 60 to 66% in the shea nut meal (Table 2).

	ACKNOWLEDGMENTS

 
The financial assistance provided by the Ghana Educational Trust Fund (GETFUND) as well as technical assistance provided for amino acid analysis by Fontaine and the staff (Degussa Feed Additives Laboratory, Germany) and saponin analysis by Adeboye Fafiolu (College of Animal Science and Livestock Production, University of Agriculture, Abeokuta, Nigeria) is gratefully acknowledged.

	FOOTNOTES

 
¹ Part of the data in this paper was presented as a poster at World Poultry Science Association UK Branch Annual Meeting (April 2007).

Received for publication July 17, 2007. Accepted for publication December 10, 2007.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dei, H. K. Articles by Pirgozliev, V. Search for Related Content PubMed Articles by Dei, H. K. Articles by Pirgozliev, V.