Nutritive value of feedstuffs for poultry in Ghana: chemical composition, apparent metabolizable energy and ileal amino acid digestibility

A Donkoh and V Attoh-Kotoku 

Department of Animal Science, Faculty of Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi - Ghana

armdonkoh@yahoo.co.uk

Abstract 

A range of Ghanaian poultry feedstuffs were evaluated for their nutrient quality. The samples were subjected to chemical analysis to obtain gross composition and apparent metabolizable energy (AME) data and also to ileal digestibility bioassay, using broiler chickens, to determine the digestibility of each of the amino acids (AA) in each of the samples of feedstuffs under evaluation.

For the cereals (maize, sorghum I and sorghum II) and cereal by-products (wheat bran, rice bran, maize bran and dried brewer’s spent grains), differences in crude protein, crude fibre and crude fat contents as well as AME and ileal digestibility of protein and amino acids were observed. The mean tannin content of low tannin sorghum (sorghum I) was determined to be 0.38%, while the corresponding value for high tannin sorghum (sorghum II) was 1.87%. Tannin content affected AME and ileal AA digestibility negatively.

For the high protein feedstuffs (fishmeal I, fishmeal II, blood meal, soyabean meal and cotton seed cake), differences were also observed among feedstuffs with respect to crude protein, fat, AME and ileal protein and AA digestibilities. Amino acids contained in blood meal are well digested by broiler chickens than amino acids contained in the other high protein feedstuffs. The fishmeal samples show a wide variation in gross compositional values, AME contents and AA digestibility coefficients. It is concluded that the digestibility of amino acids varies greatly among different feedstuffs, thus the use of digestible values rather than tabulated gross compositional values should improve the precision of dietary formulation.

Keywords: cereals, cereal by-products, high protein feedstuffs, nutritive quality, precision dietary formulation

Introduction

Maize is the most common cereal grain fed to poultry in most developing countries including Ghana and is the main source of energy. Sorghum is a cereal grain that is routinely grown in the arid and semi-arid tropical areas of the world. This crop is tolerant to drought and high temperatures and has the advantage that it can be produced on marginal soils. Grain sorghum has the potential to serve as alternative to maize in poultry diets. However, highly variable nutritional qualities have resulted in poultry and pig producers discriminating against grain sorghum as feed source. Also, little information is available about the nutritive value of Ghanaian varieties of sorghum when fed to poultry. Wheat bran, which consists almost entirely of the coarse outer coatings of the wheat kernel, is one of the most popular and important poultry feedstuffs. Other cereal by-products that are used in feeding poultry include rice bran, maize bran and brewer’s spent grains.

Fishmeal is an important constituent in poultry diets because of its high protein content, good amino acid profile and highly digestible protein in the diets of simple stomached animals, and it is therefore essential to understand all the parameters affecting protein quality. They also provide an important supply of essential vitamins and minerals as well as varying amounts of highly digestible energy (Windsor and Barlow 1981). Research data indicate that blood meal is of high nutritional value to poultry when fed in combination with other protein sources (Donkoh et al 1999, 2001). Oil seed cakes and meals are very valuable poultry feeding-stuffs. According to Church and Pond (1988), soya bean meal is one of the best plant protein sources available and is a highly favoured feed ingredient as it is of high energy value, quite palatable and results in excellent performance when used for feeding different animal species. Cotton seed cake is also a valuable component of poultry rations and is known to contain a high concentration of good quality protein (Papadopoulos and Ziras 1987).

Information on the relative ability of the different feedstuffs to supply digestible rather than total nutrients is necessary for accurate diet formulation (Furuya and Kaji 1989). The ileal measure of dietary amino acid digestibility has been shown to be superior to the faecal method in detecting small differences in the digestibility of amino acids, especially for less digestible protein sources (Sauer et al 1981).

However, no or little information on nutrient digestibility is available for Ghanaian feedstuffs, in spite of their frequent use in poultry diets. The aim of the present study was to determine and compare the apparent metabolizable energy and ileal digestibilities of total nitrogen and amino acids in a range of feedstuffs available in Ghana for feeding poultry.

Materials and methods 

Feed ingredients

One sample each of maize, wheat bran, rice bran, maize bran, brewer’s spent grains, solar-dried blood meal, soyabean meal, cotton seed cake and two samples of sorghum and fishmeal obtained from commercial feed suppliers, were evaluated in this experiment. The maize used in this study was the normal white hybrid maize. The two types of sorghum were selected based on the tannin contents. Sorghum I was a representative of a low tannin-containing sorghum and sorghum II of a higher tannin-containing sorghum. The two extreme sorghums were chosen to provide a comprehensive test of the effect of tannin on nutrient quality. The wheat bran was obtained as a by-product of the manufacture of wheat flour, while rice bran and maize bran were by-products obtained during the milling of rice and maize for human food, respectively. The dried brewer’s grains is a bulky, low energy feedstuff obtained as a brewery by-product. The two fishmeals, which differed in crude protein content (636 and 487 g crude protein kg^-1 DM), were designated as fishmeal I and fishmeal II. Fishmeal I originated from Peru. It was made from anchovies. No detailed information was available on its method of manufacture. Fishmeal II was made from waste obtained during the processing of tuna fish and contained high amounts of bones. The blood meal was made from blood obtained as a result of pig and cattle slaughterings. The blood was pre-heated for 30 mins at a temperature of 60⁰C and further dried in a solar dryer at 35 – 50⁰C to a moisture content of 100 g kg^-1 DM. The soyabean meal was the ground residue of screw-pressed soyabeans. The cotton seed cake was the residue of cotton seed oil extraction. The feed ingredients under evaluation were milled through a 3-mm hammer mill (Christy and Norris Ltd., Chelmsford UK) to produce the meals.

Animals and housing

A total of 144 male broiler chickens were placed in deep litter pens and used to determine the apparent metabolizable energy (AME) and ileal amino acid digestibility of the feed ingredients under test. Chicks were fed a commercial starter diet until 21 d of age. At 21 d of age, birds were weighed and randomly placed in battery cages, each measuring 40 x 33 x 41 cm, and fed a broiler finisher diet until 35 d of age.

Determination of apparent metabolizable energy

Seventy-two of the chickens (i.e. 6 birds per ingredient) were used to determine the apparent metabolizable energy (AME) contents of the twelve feed ingredients under test. Birds were fed ad libitum on a broiler finisher diet for 1 week prior to force-feeding (Sibbald 1986). The birds were housed in individual cages with collection trays, fasted for 24 h and force-fed 90 g of the test ingredient. Excreta were collected daily for 48 h after force-feeding, oven dried at 60⁰C for 48 h, equilibrated to ambient conditions, weighed and ground (Dale and Fuller 1983). The test ingredients and faecal samples were analysed for gross energy by bomb calorimetry.

Determination of apparent ileal nitrogen and amino acid digestibilities

Cereals and cereal by-products to be assayed were mixed with minerals and vitamins (Table 1).

High protein raw materials to be assayed were mixed with corn starch, minerals and vitamins (Table 2) in order to provide dietary crude protein (N x 6.25) concentrations of 209 g kg^-1.

Chromic oxide (0.30%) was incorporated into the diets as an indigestible marker. Seventy-two male broiler chickens were kept individually in battery cages with wire mesh floors. The broiler chickens were randomly allocated to the twelve experimental diets such that there were six birds per diet.  Each bird had free access to its respective experimental diet for a 7-d period. Diets were fed in mash form. Water was available ad libitum. At 42 d of age, birds were killed by an overdose of anaesthetic 4 h post-feeding and the terminal ileal contents (mid-way between the ileal-cecal junction and Meckel’s diverticulum and 2 cm anterior to the ileal cecal junction) were collected by slowly flushing out the contents into a plastic bag, with 10 ml deionised water from a plastic syringe. Ileal digesta samples collected from birds on a particular diet were freeze-dried over a 96-h period prior to analysis.

Chemical analysis

Samples of the feedstuffs were chemically analysed for key nutritional characteristics: dry matter, protein, ether extract, fibre and ash according to standard procedures (AOAC 1990). Samples of the ileal digesta were also analysed for nitrogen and amino acids. Amino acid contents were determined by ion exchange chromatography following hydrolysis in 6N hydrochloric acid at 110⁰C for 24 h. Methionine and cysteine were determined as methionine sulphone and cysteic acid after oxidation with performic acid. Tryptophan, being destroyed during acid hydrolysis, was not determined. The chromium contents of four 100 mg samples of each diet and triplicate 15 mg samples of ileal digesta were analysed using atomic absorption spectrophotometry (Costigan and Ellis 1987). Tannin content in sorghum was determined using the vanillin HCl method (Burns 1971).

Data analysis

Calculations to determine AME, based on faeces, were performed according to the procedure of Bartov (1995). Estimates of apparent nitrogen and amino acid digestibilities were determined using ileal samples and calculated from the dietary ratio of N or amino acids to chromium relative to the corresponding ratio in the ileal digesta. The digestibility values for the diets were taken to represent values for the feedstuffs because the other dietary ingredients were protein free. The apparent digestibility data were subjected to analysis of variance to compare differences between feedstuffs. Differences between means were examined using Duncan’s multiple range test (Snedecor and Cochran 1989).

Results and discussion 

Proximate analyses and amino acid concentrations of the feedstuffs are shown in Tables 3 and 4. Crude protein of cereals and cereal by-products varied from 82.3 in maize to 207 g kg^-1 DM in brewer’s spent grains (Table 3). Not only were the levels of protein in the cereal by-products higher than the cereal grains, but the amino acids were also higher. The crude fibre content was generally high in cereal by-products and low in the cereal grains ranging from 21.1 in maize to 164 g kg^-1 DM in brewer’s spent grains. Among the cereal grains evaluated, the content of crude protein was highest for sorghums I and II and lowest for maize. Similar to crude protein contents, the total amino acid contents were highest for sorghum I followed by sorghum II and maize. The high total amino acid contents in the grain sorghums were mainly due to the extremely high glutamic acid and leucine contents. The lysine content of maize was almost the same in the two types of grain sorghums. The highest crude protein and amino acid contents in the grain sorghums, than in maize, are consistent with other observations (Adeola et al 1994; Lawrence et al 1995; Yin et al 2002).

All of the cereal grains contained almost the same level of fat. Sorghum I contained 0.38% tannin and sorghum II contained 1.87% tannin. Among the cereal by-products, dried brewer’s spent grains are higher than wheat bran, rice bran and maize bran in protein content.

The crude protein of the high protein feedstuffs ranged from 411 in cotton seed cake to 853 g kg^-1 DM in solar-dried blood meal, with corresponding lysine contents of 19.0 and 81.4 g kg^-1 DM, respectively (Table 4). Except for fishmeal II, the crude protein and lysine contents of the protein feedstuffs of animal origin were higher than those of the plant protein sources. This is in agreement with Parkhurst and Mountney (1988) who indicated that animal proteins are generally of higher quality than those of plant origin since they are richer in the sulphur-containing amino acids. 

The values presented here for the proximate composition of solar-dried blood meal are close to the values reported by NRC (1994). The results indicate a very high concentration of protein in solar-dried blood meal. NRC (1994) reported high protein contents of 881 g kg^-1 DM for vat-dried blood meal and 889 g kg^-1 DM for spray- or ring-dried blood meal. Solar-dried blood meal contained substantial amounts of indispensable amino acids, including lysine, methionine, arginine, cystine, leucine and threonine but was very poor in isoleucine. The observed differences in nutrient composition between fishmeal I and fishmeal II also suggest variability in nutritive value with type of fishmeal. The variation in nutrient composition of fishmeal may have resulted from differences in raw materials used (i.e. differences in proportions of bone and soft tissue in the raw materials) or processing method or a combination of these two factors. Fishemal II contained considerable amounts of bone in the raw materials used for fishmeal manufacture which resulted in meal low in protein and essential amino acids, but high in ash. The amino acid profile of soya bean meal indicates it is deficient in methionine. Cotton seed cake has a lower lysine content when compared to soya bean meal.

The AME values and digestibility coefficients are presented in Tables 5 and 6. The AME values of the cereal grains and cereal by-products ranged from 5.80 MJ kg^-1 DM in wheat bran to 13.1 MJ kg^-1 DM in maize. The AME values for the cereals and cereal by-products samples were different, which is a reflection of the different compositions. In general, the AME values for cereal grains are higher than for cereal by-products probably because of the higher fibre contents of the cereal by-products. Tannins present in sorghum may impair the ability of the chicken to digest dietary nutrients. The amount of tannin present in the grain sorghum greatly influenced the AME of the samples.

Overall, the apparent digestibility values for amino acids in cereal grains are higher than for cereal by-products (wheat bran, rice bra

Schneeman (1978) has shown that both wheat bran and rice bran per se can inhibit trypsin activity in vitro. Much of the protein in the brans is involved with structural carbohydrates and the solubility of the bran protein is not high in aqueous solutions until the pH exceeds 9.0 (Connor et al 1976). This factor, combined with the presence of protease inhibitors, may reduce protein digestibility. High levels of fibre in the diet increase the rate of passage in chickens (Warren and Farrell 1991). This may also help to account for the lower apparent digestibility of amino acids from the cereal by-products. Among the cereal grains, amino acid digestibility coefficients are higher for maize than for the two types of sorghum. The sorghum coefficients are more variable and depend on the tannin content. High tannin content affects the digestibility of amino acids. For example, the results indicate that cystine digestibility is lowered by tannin content in sorghum. Tannins are a group of phenolic compounds that bind to digestive enzymes, gut proteins involved in nutrient absorption and also form nutritionally unavailable polymers with dietary proteins (Jung and Fahey 1983; de Lange 2000). This explains in part the large variability observed for the low tannin sorghum (sorghum I) and the high tannin sorghum (sorghum II). This is in agreement with the study of Cousins et al (1981) who found that the apparent ileal digestibility of amino acids in pigs fed sorghum varying in tannin concentrations (0.83, 0.88, 3.17 and 3.40 mg of catechin equivalents per 100 mg of grain) was decreased (P<0.05) as the tannin concentration increased.

The AME values of high protein feed ingredients varied from 7.80 MJ kg^-1 in cotton seed cake to 14.3 MJ kg^-1 DM in fishmeal I (Table 6). Except for fishmeal II, the apparent digestibility coefficients for amino acids in animal protein feedstuffs were higher than for those of plant origin. This could be attributed to the fact that plant proteins are more resistant to breakdown in the gastro-intestinal tract than animal proteins (Pusztai 1985; Begbie and Pusztai 1989). Amino acids contained in blood meal tended to be the most digestible. Published data (Batterham et al 1986) indicate that dried blood meal protein can be highly digestible. The nutritive value of fishmeals is highly variable and can be related to the quality and type of raw material as well as the species of fish being processed.

Lower digestibilities were found for fishmeal II because of the high amounts of bones included in the meal. Different systems used in the manufacture and the drying of the meals can also have a significant effect on quality (Johnston and Savage 1985). Severe heating during drying will lower digestibility and cause some loss of essential amino acids. For the plant protein feedstuffs, the data indicated that the amino acids contained in soya bean meal are well digested by broiler chickens than amino acids contained in cotton seed cake.

The variability shown in the nutrient composition and in the protein digestibility of the feedstuffs under evaluation is of particular importance nutritionally and economically. When these digestibility coefficients for the essential amino acids are combined with the gross amino acid values, figures which more accurately reflect the value of the protein supplied by the various feedstuffs, are generated. Thus the digestible amino acid values vary considerably between the sources. Some feedstuffs are better than others, but this can only be determined through the development of a simple, inexpensive ileal assay procedure. For example, sorghum I and sorghum II have the same gross value for lysine (2.50 g kg^-1 DM), but sorghum I provides 2.14 g kg^-1 DM digestible lysine and sorghum II only 1.98 g kg^-1 DM.

Conclusions 

• In the absence of better information, nutritionists are currently forced to use tabulated ‘average’ gross compositional values generated in other countries. Thus, dietary amino acids will be over-formulated as insurance against inclusion of poorer quality feedstuffs. Obviously, such an approach is not optimal, and is costly to the poultry producer. It is proposed to collect a wide range of feedstuffs, both conventional and non-conventional, from around the country to reflect differences in the processing plants used and the methods employed in production of certain ingredients such as fishmeal, blood meal, cotton seed cake and soyabean meal. By the use of standard evaluation technique it is hoped to develop mathematical equations to allow the prediction of the quality of a feedstuff from its chemical and/or physical characteristics. In this way, it may be possible to provide a means by which the prices will more accurately reflect the value of the product to users. Producers will thus be able to make more informed decisions on the purchase of feedstuffs.

References 

Adeola O, Rogler J C and Sullivan T W 1994 Pearl millet in diets of White Peking ducks. Poultry Science 73: 425

Association of Official Analytical Chemists 1990 Official Methods of Analysis. 15^th edition. Association of Official Analytical Chemists, Arlington, Virginia

Bartov I 1995 Differential effect of age on metabolizable energy content of high protein-low energy and low protein-high energy diets in young broiler chicks. British Poultry Science 36:  631 – 643

Batterham E S, Lowe R F,  Darnell R E and Major E J 1986 Availability of lysine in meat meal, meat and bone meal and blood meal as determined by the slope-ratio assay with growing pigs, rats and chicks and by chemical techniques. British Journal of Nutrition 55: 427 –  440

Begbie R and Pusztai A 1989 The resistance of proteolytic breakdown of some plant (seed) proteins and their   effects on nutrient utilization and gut metabolism. In: M. Friedman (editor). Absorption and Utilization of Amino Acids. Volume III. CRC Press, Boca Raton Fl. p. 241 – 263

Burns R E 1971 Method for estimation of tannin in sorghum grain. Agronomy Journal 63:  511 – 512

Church D C and Pond W G 1988 Basic Animal Nutrition and Feeding. 3^rd Edition. John Wiley and Sons Inc., New York

Connor  M A,  Saunders R M and Kohler G O 1976 Rice bran protein concentrate prepared by wet extraction. Cereal Chemistry  53: 488 –  496

Costigan P and Ellis K J 1987 Analysis of faecal chromium derived from controlled-release marker devices. New Zealand Journal of Technology 3:  89 – 92

Cousins Jr B W, Tanksley T D, Knabe D A and Zebrowska T 1981 Nutrient digestibility and performance of pigs fed sorghums varying in tannin concentration. Journal of Animal Science 53: 1524 – 1537 http://jas.fass.org/cgi/reprint/53/6/1524

Dale N M and Fuller H L 1983 Oven drying vs. freeze drying of excreta in true amino acid availability and true metabolizable energy assay. Poultry Science 62: 1407 – 1408

de Lange C F M 2000 Characterization of non-starch polysaccharides. In: P J Moughan, M W A Verstegen and M I Visser-Reyneveld (editors). Feed evaluation: Principals and Practice. Wageningen Pers, Wageningen. pp. 77 – 88

Donkoh A, Atuahene C C,  Anang D M and Ofori S K 1999 Chemical composition of solar-dried blood meal and its effect on performance of broiler chickens. Animal Feed Science and Technology 81: 299 – 307

Donkoh A, Anang D M, Atuahene C C, Koomson B and Oppong H G  2001 Further studies on the use of solar-dried blood meal as a feed ingredient for poultry. Journal of Animal Feed Science 10: 159 – 167

Furuya S and Kaji Y 1989 Estimation of the true ileal digestibility of amino acids and nitrogen from the apparent values for growing pigs. Animal Feed Science and Technology 26: 271 – 285

Johnston J N and Savage G P 1985 Nutritive value of New Zealand produced fish meal. Proceedings of the Nutrition Society of New Zealand 10: 73

Jung H G and Fahey G C Jr 1983 Nutritional implications of phenolic monomers and lignin: a review. Journal of Animal Science 57: 206 – 219 http://jas.fass.org/cgi/reprint/57/1/206

Lawrence B V, Adeola O and Rogler J C 1995 Nutrient digestibility and growth performance of pigs fed pearl millet as a replacement for corn.  Journal of Animal Science 73: 2026 - 2032 http://jas.fass.org/cgi/reprint/73/7/2026.pdf

National Research Council 1994 Nutrient Requirements of Domestic Animals. Nutrient Requirements of Poultry. 9^th revised Edition. National Academy Press, Washington, DC

Papadopoulos G and Ziras E 1987 Nutrient composition of Greek cotton seed meal. Animal Feed Science and Technology 18: 295 – 301

Parkhurst C R and Mountney G J 1988 Poultry Meat and Egg Production. Avi Nostrand Reinhold Co. Inc., New York, p. 701 – 702

Pusztai A 1985 Constraints on the nutritional utilization of plant proteins. Nutrition Abstracts and Reviews (Series B) 15: 363 – 369

Sauer W C, Kennelly J J,  Aherne F X and Chicon R M 1981 Availabilities of amino acids in corn, wheat and barley for growing pigs. Canadian Journal of Animal Science 57: 585 – 597

Schneeman B O 1978 Effect of plant fibre on lipase, trypsin and chymotrysin activity. Journal of Food Science 43: 634 – 638

Sibbald I R 1986 The TME System of Feed Evaluation: Methodology, Feed Composition Data and Bibliography. Animal Research Centre Contribution 85-19, Ontario

Snedecor G W and Cochran W G 1989 Statistical Methods. 8^th Edition. Iowa State University Press, Ames

Warren B E and Farrell D J 1991 The nutritive value of full-fat and defatted Australian rice bran. V. The apparent retention of minerals and apparent digestibility of amino acids in chickens and adult cockerels fitted with ileal cannulae. Animal Feed Science and Technology 34: 323 – 342

Windsor M and Barlow S 1981 Introduction to Fishery By-Products. Fishing News Books Ltd., Farnham, England

Yin Y L, Gurung N K, Jeaurond E A, Sharpe P H and de Lange C F M 2002 Digestible energy and amino acid contents in Canadian varieties of sorghum, pearl millet, high-oil corn, high-oil-high-protein corn and regular corn samples for growing pigs. Canadian Journal of Animal Science 385 – 391

Received 16 December 2008; Accepted 23 December 2008; Published 10 March 2009

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