Nutritional evaluation of sorghum germ meal as a substitute for sorghum in broiler diets

Animal Feed Science and Technology, 44 ( 1993 ) 93-100

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0377-8401/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved

Nutritional evaluation of sorghum germ meal as a substitute for sorghum in broiler diets E.A. Elzubeir*, S.K. Jubarah Institute of Animal Production, Universityof Khartourn, Khartoum North, Shambat, P.O. Box 32, Sudan (Received 10 September 1991; accepted 11 May 1993)

Abstract

Sorghum germ meal (SGM) samples were analysed for proximate composition and then fed to broiler chicks as a substitute for sorghum, on an isoenergetic basis. At the lowest levels of inclusion SGM replaced 0, 25 and 50% and at the highest levels 75 and 100% of sorghum apparent metabolizable energy (AME). On average, SGM contained 989.8 g kg-~ dry matter, 126 g kg-1 crude protein, 280 g kg -1 ether extract, 45.4 g kg -~ crude fibre, 39.39 g kg -~ ash, 0.1 g kg-1 calcium, 0.4 g kg -~ phosphorus, 2250 mg ( 100 g)-1 phytic acid equivalent and 17.92 MJ kg-~ calculated metabolizable energy. Increasing SGM inclusion resulted in increasing dietary crude fibre and phytic acid content. Increased dietary SGM levels resulted in a linear reduction in body weight (P< 0.01 ) and weight gain (P< 0.05), and a decrease in feed intake. The feed:gain ratio showed a linear increase (P< 0.01 ). Dressing percentage, pancreas and abdominal fat relative weights showed a linear increase (P< 0.01 ) in response to increase in SGM. Bursa relative weight was not influenced by dietary SGM inclusion. Replacement of more than 25% of sorghum AME with SGM AME resulted in poor broiler performance.

Introduction Sorghum is the leading cereal crop in the Sudan. It constitutes the main staple food and a raw material for industrial processing. Sorghum is wet milled primarily to produce starch or starch hydrolysed to glucose. Sorghum germ meal (SGM) is the first by-product of that process, and is separated from the heavier endosperm in a continuous liquid cyclone after grinding in an attrition mill (Kent, 1983 ). The other two by-products, sorghum gluten feed and gluten meal, have been evaluated in poultry diet by Elzubeir et al. (1990) and Hamid and Elzubeir (1990), respectively. SGM production in Sudan has increased steadily from 25 000 t in 1989 to 75 000 t in 1990. It is of high energy and low protein content, with an oil content ranging between 18.5% and 30.8% (Hulse et al., 1980). We have little information on the nutritive value of this by-product, but it is presumed to *Corresponding author.

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make a worthwhile contribution in poultry rations. The present study was conducted to evaluate the effect of replacement of sorghum with SGM on broiler chicks' performance. Materials and methods Two tons of SGM were obtained from the Sudanese Arab Starch and Glucose Company, and composite samples were analysed for proximate composition, calcium, phosphorus and phytic acid content (Table 1 ). Five experimental diets were formulated; these consisted of a control diet with sorghum (Feterita) as the main cereal source, and four other diets in which sorghum was replaced by increasing amounts ( 126.9, 253.8, 380.7 and 507.6 g kg-~ ) of SGM on an isoenergetic basis (Table 2). These levels will replace 25, 50, 75 and 100% of the apparent metabolizable energy contributed by sorghum in the control diet. The experimental diets were formulated to meet the requirements for essential nutrients as outlined by the National Research Council (1984). They were calculated to be isonitrogenous, isoenergetic, and equal in sulphur amino acids and lysine. The calculated composition of the diets (Table 2 ) was based on the actual analysis of ingredients used. Six hundred 1-day-old unsexed, commercial hatchery chicks were sexed and fed a control diet (Table 2 ) for a period of 7 days. At the end of the seventh Table 1 Chemical composition of sorghum germ meal (SGM) (g kg - ~) Component

As-fed basis

Dry matter Crude protein ( N × 6.25) Ether extract Crude fibre Ash Calcium Phosphorus Nitrogen-free extract ( N F E ) Metabolizable energy ( ME ) ( M J k g - 1) Phytic acid ( m g per 100 g)

989.80 126.00 280.35 45.40 39.34 0. l 0 0.40 508.91 17.92 2250.00

Amino acid values i (g k g - 1)

Lysine Methionine Cystine Tryptophan Leucine Isoleucine

4.0 5.0 4.0 1.0 3.0 6.0

N F E is a calculated value. ME is calculated from the equation of Lodhi et al. (1976). ~Analysed values are means of duplicate samples.

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Table 2 Composition and analysis of the experimental diets (g kg- ~) Ingredient

% ME substitution of SGM for sorghum 0.00

Sorghum Sorghum germ meal Groundnut meal Sesame meal Cotton seed oil FillerI Bone meal Oyster shell L-lysine HCI DL-methionine Salt Vitamin and mineral premix2

621.1 0.0 215.3 100.1 14.2 0.0 27.3 7.64 7.76 2.1 2.5 2.0 1000

25 465.7 126.9 190.0 141.0 8.97 21.7 26.76 5.9 7.31 1.26 2.5 2.0 1000

50 310.5 253.8 190.0 154.0 4.8 42.69 27.1 5.1 6.85 0.66 2.5 2.0 1000

75 155.3 380.7 188.8 170.0 0.0 62.78 27.1 4.4 6.39 0.03 2.5 2.0 1000

100 0.0 507.6 196.0 174.3 0.0 79.89 27.7 4.0 6.0 0.01 2.5 2.0 1000

Calculated composition

ME (MJ kg- ~) Crude protein Lysine Methionine Tryptophan Calcium Available phosphorus Phytic acid3

13.39 230.2 12.0 5.0 2.31 12.0 5.0 0.0

13.38 230.2 12.0 5.0 2.38 12.0 5.0 2.86

13.39 230.2 12.0 5.0 2.39 12.0 5.0 5.71

13.38 230.9 12.0 5.0 2.43 12.0 5.0 8.87

13.52 230.5 12.0 5.0 2.43 12.0 5.0 11.42

964.2 242.3 36.2 67.1 81.1 0.51

954.1 240.6 30.3 80.7 118.2 0.46

959.1 232.7 54.4 93.8 131.4 0.47

966.0 241.5 65.3 121.6 157.1 0.47

950.6 229.3 81.3 187.6 128.6 0.48

D e t e r m i n e d analysis

Dry matter Crude protein (N× 6.25 ) Ether extract Crude fibre Ash Specific gravity

tSand was used as an inert filler. 2Vitamin and mineral premix provides (per kilogram diet): vitamin A 15 00 IU, vitamin D3 3000 IU, vitamin B1 2 mg, vitamin B2 5.5 mg, vitamin BI2 0.01 mg, D-calcium pantothenate 10 mg, vitamin E 5 mg, vitamin K 3 mg, niacine 25 mg, choline chloride 120 rag, ethoxyquin l0 mg, manganese oxide 32.26 mg, potassium iodide 0.706 mg, cobalt sulphate 0.572 mg, zinc oxide 25 mg, copper oxide 2.566 mg, ferrocarbonate 40.646 mg. 3Phytic acid contributed by SGM inclusion. day, 250 chicks were selected by discarding the lightest and heaviest, and were r a n d o m l y a l l o c a t e d i n t o 25 p e n s , i n g r o u p s o f 10 c h i c k s ( f i v e m a l e a n d f i v e f e m a l e t o n e g a t e sex d i f f e r e n c e s ) p e r p e n , i n a n o p e n - s i d e d d e e p - l i t t e r p o u l t r y house. The experimental diets (Table 2 ) were randomly assigned to the pens (five pens per dietary treatment). Feed and water were provided ad libitum,

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and a 24 h photoperiod was maintained throughout the 6 week experimental period. Records were kept daily for mortality and weekly for live weight and feed consumption. Leg abnormalities were determined by subjective evaluation of each bird; only chicks showing a medium or severe degree of bowing were considered to be abnormal. At the end of the sixth week of the experimental period the birds were starved of feed for 18 h, then four chickens (two male and two female) were selected on the basis of average pen weight from each dietary replicate (pen). They were individually weighed, tagged, slaughtered, scalded, manually plucked and allowed to drain on a wooden table. Eviscerated carcass and organ weights were recorded and dressing percentage was determined.

Chemical and statistical analysis Chemical analysis of SGM and the experimental diets was carried out according to the standard methods (Association of Official Analytical Chemists, 1974). The phytic acid content of SGM was determined by the method of Wheeler and Ferrel ( 1971 ), and the metabolizable energy content of SGM was calculated from its chemical composition by the equation of Lodhi et al. (1976). The specific gravity of each experimental diet was determined by comparing the weight of a measured volume of feed ( 100 ml) with the weight of the same volume of distilled water. The amino acid content of SGM was determined at Hanover University, Germany. The protein was hydrolysed with 6 N hydrochloric acid and the hydrolysate was treated with 9-fluorenylmethylchloroformate, then the amino acid derivatives were separated using reversed-phase chromatography and measured in a fluorometer at 260 nm (extinction) and 310 nm (emission). Methionine and cystine were determined after oxidation to methionine sulphone and cystic acid, respectively. The data obtained were subjected to analysis of variance, and significant effects were partitioned into linear and quadratic components to evaluate the responses of those effects, as described by Snedecor and Cochran ( 1971 ). Results

The results of the proximate analysis, calculated metabolizable energy and phytic acid equivalent of SGM are presented in Table 1. In comparison with sorghum, millet, maize, wheat and barley (National Research Council, 1984), SGM is superior with respect to metabolizable energy and ether extract, and contains considerably less calcium and more phosphorus and crude fibre. With the exception of wheat and millet, SGM contained more crude protein than the other cereals. The results shown in Table 3 demonstrate that inclusion of SGM in diets for broiler chicks depressed final body weight, and increased (feed: gain ratio,

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Table 3 Effect on broiler chicks' performance of feeding sorghum germ meal (SGM) (age of chicks at end of test was 7 weeks) SGM: sorghum substitution (%)

Final body weight (g per bird)

Feed intake (g per bird)

Weight gain (g per bird)

Feed: gain ratio (gg-l)

Incidence of leg abnormality (%)

Mortality

0:100 25:75 50:50 75:25 100:00 ±Pooled SEM

1821 1745 1441 1310 1116 30.9Lb

3574 3349 3131 3071 2985 62.6

1748 1669 1365 1235 1040 30.3 ¢

2.05 2.01 2.30 2.49 2.87 0.04 ",b

2.0 0.0 2.0 4.0 12.0 1.77

6.0 2.0 6.0 6.0 8.0 1.81

(0~)

"Linear effect significant ( P < 0.01 ). bQuadratic effect significant ( P < 0.01 ). CLinear effect significant (P< 0.05 ). Table 4 Dressing percentage, viscera, abdominal fat, and relative weight of organs (expressed as % body weight) (chicks were fed a control diet or one of few levels of SGM substitution for sorghum, and were aged 7 weeks at slaughter) SGM: sorghum substitution

Dressing percentage

Liver

Pancreas

Bursa

Abdominal fat

Viscera

00:100 25:75 50:50 75:25 100:00 +Pooled SEM

67.72 65.40 63.78 62.07 59.70 0.80 a

2.03 2.24 2.60 2.59 3.03 0.09 a'b

0.27 0.23 0.27 0.29 0.30 0.01 a

0.23 0.23 0.23 0.23 0.22 0.02

0.98 0.75 0.76 0.54 0.39 0.11 a

20.77 22.66 25.99 26.38 28.99 0.9 ~,b

aLinear effect significant ( P < 0.01 ). bQuadratic effect significant ( P < 0.01 ).

which both showed linear (P< 0.01 ) and quadratic (P< 0.01 ) responses. The dietary SGM substitution reduced feed intake and weight gain, which showed linear (P< 0.05) responses. The results in Table 4 show that dressing percentage and abdominal fat relative weight decreased with increase in the dietary SGM level (P<0.01), whereas liver and viscera relative weights increased, showing linear (P<0.01) and quadratic (P<0.01) responses, and pancreas relative weight showed a linear (P< 0.01 ) effect. Increasing dietary substitution of SGM did not result in a significant change in bursa relative weight, and neither mortality nor incidence of leg abnormalities were affected, although they tended to increase with increasing level of SGM. Discussion The chemical analysis of SGM used in the present experiment gave values (Table 1 ) which are at variance with those reported by Kent (1983), as the

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SGM it has slightly higher crude protein and lower oil content. The determined phytic acid equivalent ( 2.25% ) is higher than the highest limit ( 1.31% ) specified by Hulse et al. (1980). These compositional variations are attributable to sampling procedure, blended proportions of the other by-products or cultivar differences. The poor performance of chicks associated with feeding SGM observed in this study confirms the findings of Jubarah and Elzubeir (1992 ). It can be seen from the calculated and determined composition of the experimental diets (Table 2) that their crude fibre and phytic acid contents increased as a result of increasing the SGM substitution level. Owing to the high oil content of SGM, which is consistent with the increasing determined dietary ether extract, one could speculate on the role of the increasing use of inert filler (sand) in the SGM dietary treatments. Results reported by Farjo et al. (1986) showed that broilers were able to regulate their feed intake to ensure sufficient nutrient intake to satisfy their requirement, and birds given sand-diluted diets increased their feed consumption in proportion to the inclusion rate of sand, thus compensating for the reduction in nutrient density. Accordingly, one might expect similar live weights for all dietary treatments, as sand aids in the grinding of feed particles. The results obtained in this study agree with the findings of Cabel and Waldroup (1990), who reported that sand may not have the bulk necessary to restrict nutrient intake, as shown by decreasing feed intake and body weight gain, which may suggest that the beneficial consequences might have been negated by the increasing SGM level, in addition to the reduction in the proportion of readily digestible starch that would have been contributed by the replaced sorghum. The slight reduction in specific gravities of the dietary treatments from that of the basal diet indicates that factors other than the reduced bulkiness of the diets contributed to the reduced performance of chicks, as the increment in dietary filler might offset the increasing effect of crude fibre on the bulkiness of the dietary treatments. The increase in crude fibre content of the diets containing SGM may in part explain the poor weight gain and feed utilization, which seemed to be due to an interaction between the feeding levels and the digestibility of the nutrient. Kondra et al. (1974), Deaton et al. (1979) and Abdelsamie et al. (1983) have reported that high dietary fibre content increased viscera relative weight, which is consistent with the result obtained in this study. The linear reduction in abdominal fat of chicks fed increasing levels of SGM is consistent with the finding of Gous et al. (1990), who showed that the abdominal fat content was generally reduced by diluting the feed with dietary fibre, which also reduced live weight gain. The increase in liver and pancreas relative weights may suggest that the metabolic functions such as digestion, nutrient transport and the excretion of metabolic products were enhanced by feeding SGM. Although there are no specific data on phytic acid effect on broiler performance, its effect on performance of chicks used in this study

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c a n n o t b e r u l e d out, as p h y t i c acid has b e e n s h o w n to h a v e chelating a n d p r o t e i n b i n d i n g effects ( L i k u s k i a n d F o r b r e , 1964; N e l s o n et al., 1971; O ' D e l l a n d de B o l a n d , 1976; N w o k o l o a n d Bragg, 1977; D o h e r t y et al., 1981; B a l l a m et al., 1 9 8 4 ) . Visual o b s e r v a t i o n s i n d i c a t e d t h a t levels a b o v e 50% S G M s u b s t i t u t i o n for s o r g h u m s e e m e d to i n f l u e n c e e x c r e t a consistency. E x c r e t a a r o u n d the cloaca were sticky, a n d d r o p p i n g s in the p e n s were wet. T h e d i e t a r y t r e a t m e n t s did n o t significantly i n f l u e n c e m o r t a l i t y a n d i n c i d e n c e o f leg a b n o r m a l i t i e s , despite the t e n d e n c y o f b o t h to increase w i t h d i e t a r y S G M substitution. A l t h o u g h S G M has h i g h e r a p p a r e n t m e t a b o l i z a b l e energy a n d p r o t e i n cont e n t t h a n s o r g h u m , S G M c a n n o t be u s e d as a s u b s t i t u t e for s o r g h u m at the levels t e s t e d in this e x p e r i m e n t . T h e high fibre a n d p h y t i c acid c o n t e n t o f S G M m a y be c o n t r i b u t i n g factors.

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