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Rapid Tests of Wheat Nutritive Value for Growing Chickens
Journal of Cereal Science 34 (2001) 181–190 doi:10.1006/jcrs.2001.0390, available online at http://www.idealibrary.com on
Rapid Tests of Wheat Nutritive Value for Growing Chickens S. P. Rose∗‡, L. A. Tucker∗§, P. S. Kettlewell† and J. D. A. Collier∗ Harper Adams University College, ∗National Institute of Poultry Husbandry; †Crop and Environment Research Centre, Edgmond, Newport, Shropshire TF10 8NB U.K. Received 25 July 2000
ABSTRACT Two series of broiler chicken feeding experiments quantified the differences in growth performance of broiler chickens fed either six different U.K. wheat cultivars from one harvest year or six wheat samples that comprised two cultivars (Dean and Beaver) each grown in three harvest years. Differences in broiler growth performance were compared to four rapid tests of wheat quality (specific weight, Hagberg falling number, water-extract viscosity and endosperm hardness) and the determined true metabolisable energy. Broilers fed the cultivar Dean had higher (P<0·001) weight gains and lower (P<0·05) feed conversion ratios compared to those fed Beaver. Samples from a harvest year (1992) in which there was high rainfall in the month during which harvest occurred resulted in lower (P<0·05) broiler feed conversion ratios. Endosperm hardness and water-extract viscosity were both linearly related (P<0·05) to differences in broiler feed conversion ratios but there was no (P>0·05) reduction in unaccountable variation from including both variables in a multiple regression analysis. The measurement of endosperm hardness by near infra-red spectroscopy is rapid and has the potential to be used to discriminate nutritive value between wheat samples on their arrival at poultry feed mills. 2001 Academic Press
Keywords: wheat, nutrition, chickens, hardness, viscosity.
INTRODUCTION Proprietary broiler chicken feeds contain up to 70% by weight of cereals. The choice between cereals primarily depends upon their relative price per unit of available energy, and wheat is the main cereal used in broiler chicken feeds in most northern European countries. Within the U.K. for example, 5·4 million tonnes of home-produced wheat are used in animal feeds1 and the broiler chicken industry (750 million birds per annum) uses approximately 20% of this total. Wheat will typically provide 55% of the metabolisable energy
‡ Corresponding author. E-mail: [email protected] § Current Address: Finnfeeds International Ltd, Marlborough, SN8 1AA, U.K. 0733–5210/01/050181+10 $35.00/0
(ME) and 35% of the protein supplied in a proprietary wheat-based broiler feed. Economically efficient broiler feeds must achieve a low feed conversion ratio (FCR) (kg feed eaten per kg of weight gain) but also allow the birds to maximise their rates of weight gain. There is evidence that the FCRs and growth rates of broiler chickens are affected by the use of different wheat samples2. The poultry feed industry needs reliable tests to indicate the nutritional value of the different wheat samples that they receive at their mills. Commercial feed mills may determine the content of moisture, crude protein and ether extract by near- infra red spectroscopy (NIR) on incoming grain samples, however, none of these proximate nutrients are good indicators of the resulting broiler chicken growth performance. Specific 2001 Academic Press
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weight (test weight) of the sample is another rapid measurement that may be used to indicate nutritional quality of a wheat sample. However, there is also a poor relationship between specific weight of wheat samples and the growth performance of chickens3. The specific weight of wheat samples can be affected by cultivar, agronomic and environmental factors that may not also affect the nutritional value of the wheat sample4. Polysaccharides comprise up to 80% of wheat grain, thus variation in their composition could have major effects on the nutritional value of a wheat sample. Tests that measure different characteristics of the polysaccharide content of wheat could possibly relate to differences in nutritional value. Three rapid tests are currently available that meet this criterion. Wheat viscosity is related to the content of soluble non-starch polysaccharides in wheat5 and is linearly related to the differences in in vivo digesta viscosity when wheat samples are fed to broiler chickens6. Hagberg falling number is related to the reciprocal of alpha-amylase activity in wheat grains7 and endosperm hardness is related to the milling characteristics and subsequent rate of gelatinisation of starch granules8. Total starch and non-starch polysaccharides are correlated with the metabolisable energy (ME) content of wheat9, but variation in the determined ME between wheat samples may not be a good indicator of the growth performance of broiler chickens given the samples in nutritionally complete diets. A review of published experiments established that differences in broiler FCRs and growth rates due to feeding different wheat samples were not correlated with differences in the determined ME10. There is a lack of information on the variation in the characteristics of the wheat starch and its nutritional value for poultry. There is little variation in the digestibility of wheat starch when fed to chickens but chemical or structural characteristics may affect the efficiency of utilisation of the digestible starch11. Wheat starches are a mixture of amylose and amylopectin and the ratio of these two components can vary12. Variation in starch granule characteristics may result in different rates of starch digestion that affect the efficiency of utilisation of the digestible starch. In summary, there is a lack of information that indicates if laboratory tests are related to broiler chicken growth performance when wheat samples are fed in nutritionally complete diets. Differences in growth performance have been observed between
different wheat cultivars and the same cultivars grown in different locations or in different harvest years. A laboratory test needs to detect the cultivar and environmental effects and needs to provide results quickly to allow rapid throughput of wheat samples through commercial poultry feed mills. The present study had four main objectives that involved two series of broiler chicken feeding experiments. The main objectives were: (1) to quantify the differences in growth performance of broiler chickens fed nutritionally complete diets containing one of six different U.K. wheat cultivars from one harvest; (2) to quantify the differences in growth performance of broiler chickens fed nutritionally complete diets containing one of six wheat samples that comprised two cultivars (Dean and Beaver) each grown in three harvest years; (3) to relate broiler chicken growth performance (growth rate, feed intakes and feed conversion ratio) to the proximate nutrient composition and four rapid tests of wheat quality (specific weight, water-extract viscosity, Hagberg falling number and endosperm hardness); (4) to relate any rapid test that was selected to differences in the polysaccharide content of the wheat (non-starch polysaccharides, available starch and amylose: amylopectin ratio) and the determined true ME.
EXPERIMENTAL Wheat samples For Experiment 1, the cultivars Beaver, Brigadier, Dean, Riband, Haven and Rialto were grown in the 1994 harvest year in three randomised blocks at Harper Adams College in Shropshire. Initial inspection of the broiler chicken experiment data indicated that there were significant differences in broiler growth performance due to cultivar. Two cultivars that gave significantly different growth performance were selected and further samples of these two cultivars were sourced that had been grown in different harvest years. Samples of Dean and Beaver were obtained that had been grown in three randomised blocks in each of the three harvest years 1990, 1991 and 1992. The cultivars were grown at two sites (Escrick Park and Hornsea, Yorkshire, U.K.) in 1990 and at Harper Adams College in the 1991 and 1992 harvest years. The crops were managed according to typical U.K. commercial wheat production methods with applications of fertiliser, herbicide, fungicide,
Nutritive value of wheat for chickens
insecticide and growth regulator as necessary to optimise yield. Equal amounts of grain of each cultivar from the three randomised blocks was pooled to give one sample for milling from each cultivar in each year. Grain from the two sites in 1990 was pooled. In addition, wheat samples were mixed in a horizontal mixer before hammer milling using a 2-mm screen. Stored grain from all years was freshly milled for each feeding experiment. Wheat grain analyses Dry matter, crude protein, crude fibre, ether extract and Hagberg falling number were determined using AOAC13 procedure numbers 925·10, 984·13, 962·09, 920·39 and 976·13 respectively. Endosperm hardness was measured following the AOAC procedure number 983·03 using an Oxford QN 1000 near infra-red reflectance (NIR) analyser (Oxford Instruments, Oxford, U.K.) with the 1992 Beaver sample used as the zero calibration point. The specific weight of the grain was measured using a chondrometer. The water extract viscosity was determined by soaking a 2-g sample of wheat in 4 mL of water at 30 °C for 30 min. The sample was centrifuged at 10 000×g for 2 min and the viscosity of the supernatant was measured in a rotating cone and cup viscometer (model DVII+LV, Brookfield, Stroughton, MA, U.S.A.). The total starch, amylose and amylopectin content of the wheat samples was determined using a procedure devised by Gibson et al.14 (amylose/ amylopectin assay kit, Megazyme International Ireland Ltd., Bray, Ireland). Total non-starch polysaccharide (NSP) concentration was measured using an enzymatic technique involving hydrolysis with amylase, pullulanase and pancreatin15 (Englyst Fiberzym kit for colorimetry, Dunn Nutrition Centre, Cambridge, U.K.). The total NSP concentration was further subdivided into the soluble and insoluble fractions. Metabolisable energy determinations Nitrogen-corrected true metabolisable energy (TMEn) concentrations were determined. The experimental protocol followed, with some minor alterations, a previously published technique16. A flock of 24 adult ISA Brown cockerels with a mean body weight of 3·2 kg were housed singly in cages kept in an environmentally controlled room. The
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TMEn determination involved deducting from a bird’s gross energy intake the total gross energy produced in the excreta in the subsequent 48 h. Access to feed was withdrawn from the previously ad libitum fed cockerels and after 24 h they were given a sucrose solution that provided 35 g of sucrose. After a further 24 h each cockerel was given 50 g of a ground wheat sample that was intubated directly into the bird’s crop. The total amount of gross energy excreted was corrected for endogenous energy excretion. Endogenous energy excretion was estimated at each determination by feeding 35 g of sucrose in solution to three of the cockerels, in replacement for the test wheat sample. Data from all birds was nitrogen-corrected to adjust for the nitrogen in the excreta that was derived from body protein catabolism. A correction factor of 32MJ was applied per kg of nitrogen excreted that was in excess of the amount fed. All excreta samples were dried at 60 °C immediately following the collection period. A total of nine replicate TME determinations were made for each wheat sample. Gross energy determinations of the wheat and excreta samples were made in an adiabatic bomb calorimeter (Parr-1755, Parr Instruments Company, Moline, IL, U.S.A.).
Chicken growth comparisons Two separate experiments were performed to examine differences in the growth performance of broiler chickens when fed diets containing 700 g/ kg of each of the wheat samples. Both experiments compared the growth performance of the broilers fed six wheat samples. Experiment 1 compared the six wheat cultivar samples from the 1994 harvest year. Experiment 2 compared the two wheat cultivars, Dean and Beaver, grown in the 1990, 1991 and 1992 harvest years. Identical procedures were used for the two experiments except that they were conducted at different times using different batches of broiler chickens. The experimental feeds were produced by mixing 700 g/kg of each of the ground wheat samples with other feed ingredients (Table I). No adjustment was made to account for the small differences in nutrient compositions of the wheat samples. The overall nutrient composition of the final diets was formulated to exceed the NRC17 specified nutrient requirements of this age of broiler chicken by a minimum of 15% for all essential amino acids and fatty acids. Any possible
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Table I The ingredient composition and calculated composition of the diets in two broiler chicken growth experiments Ingredient
Proportion (g/kg)
Experimental wheat (ground) Full fat soya bean (micronised) Fish meal Meat and bone meal -Methionine Vitamin and trace mineral premixa
700 155 97·5 25 2·5 20
Calculated nutrient composition Metabolisable energy (MJ/kg) Crude protein (g/kg) Lysine (g/kg) Methionine plus cystine (g/kg) Calcium (g/kg) Phosphorus (g/kg) Sodium (g/kg)
12·3 215 12 9 11 7 3
a Proprietary supplement that provided vitamins and trace elements as specified by NRC17. In addition, the premix provided 6·25 mg/kg of an anticoccidial drug (amprolium) and 0·4 mg/kg and 0·5 mg/kg respectively of two antimicrobial growth promoters (ethopabate and avoparcin).
variation in amino acid or fatty acid availability that occurred between the wheat samples would therefore have had little, or no, effect on the growth performance of the chickens. There are presently no reliable rapid methods that detect nutrient availability in wheat grains, so the procedure of using fixed wheat inclusion rates is relevant to the commercial poultry feed industry which would deal with different batches of wheat in a similar manner. Ninety-six day-old male Ross hybrid broiler chickens were fed a proprietary broiler starter feed and kept in a littered floor pen for 7 d. The birds were then randomly allocated to 48 cages with two birds being placed in each cage. The cages were 0·3 m high and had a floor area of 0·09 m2. The birds were given ad libitum access to feed and water from troughs attached to the front of the cages. The cages were kept in a controlled environment room that was initially kept at 30 °C and gradually reduced to 25 °C over the 14 d experimental period. Thirty minutes of darkness were given each 24 h. There were two sets of cages within the room and each set had six cages on each of four tiers. Each cage of birds within a sixcage tier was randomly given one of the experimental diets. The birds were given the diets for 14 d and feed intake and weight gains of the birds were measured.
Statistical analysis The differences between the wheat samples within a broiler growth experiment were compared by a randomised block analysis of variance using cage tiers as blocks. Comparisons of the samples from the 1990, 1991 and 1992 harvest years used a factorial analysis (cultivar×growing season) to compare main treatment effects and their interactions. Differences in TMEn between the wheat samples were compared by a randomised block analysis using the time repetitions as the blocking factor. The relationship between the growth performance of the broiler chickens and the proximate chemical composition and the four rapid tests of wheat quality were first examined by calculating a correlation coefficient matrix and, second, examined by a multiple linear regression technique. The two broiler growth experiments were used as a blocking factor. The data for specific weight were found to be skewed, therefore they were natural log transformed before the statistical analysis was performed. The relationship between any of the four rapid tests of wheat quality and the determined polysaccharide composition of the wheat samples was examined by a multiple linear regression technique. No blocking factors were necessary. RESULTS There were significant differences (P<0·05) in growth due to the six different wheat cultivar samples in Experiment 1. The growth of the chickens fed Brigadier was greater (P<0·05) than those fed Beaver, although the FCR of these two treatment groups was similar. Both the growth and FCR of the birds given Dean tended (P>0·05) to be higher than those fed Beaver. Samples of both Dean and Beaver cultivars could be obtained from stored wheat from the 1990, 1991 and 1992 harvest years, so experimental comparisons were continued with these six wheat samples (two cultivars×three harvest years). The results of the second broiler experiment confirmed that the birds fed the Dean cultivar samples had significantly greater weight gain (P<0·001) and feed intake (P<0·01) than those fed Beaver samples. The experiment also demonstrated that the growing season affected broiler growth performance. The birds given samples from the 1992 harvest year had significantly lower
Nutritive value of wheat for chickens
Table II
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Comparison of six cultivars grown in 1994 for wheat characteristics and broiler performance Beaver
Dean Brigadier Rialto
Riband
Haven
SEa
Significance
Proximate nutrient composition Dry matter (g/kg) Crude protein (g/kg) Ether extract (g/kg)
872 128 13
870 118 11
873 127 13
873 132 14
871 118 15
871 121 14
— — —
— — —
Rapid tests of wheat quality Hagberg falling number (s) Specific weight (kg/hL) Hardness (arbitrary units) Water-extract viscosity (cP)
322 76·4 32·0 7·0
440 77·8 95·2 4·1
380 77·1 79·9 5·2
403 76·9 85·5 5·7
291 77·4 58·9 3·4
400 77·3 46·4 8·2
— — — —
— — — —
Polysaccharide characteristics Total starch (g/kg) Amylose: amylopectin Total NSP (g/kg) Insoluble NSP (g/kg) Soluble NSP (g/kg)
640 662 659 660 631 629 0·492 0·466 0·481 0·491 0·506 0·500 98 101 101 105 92 94 73 84 81 87 74 68 25 17 20 18 18 26
— — — — —
— — — — —
13·98
0·462
NS
0·503 0·822 1·637
0·0211 0·0313 0·0561
∗ NS NS
In vivo determined metabolisable energy TMEn (MJ/kg DM) 14·51 Broiler growth performance Weight gain (kg/bird) Feed intake (kg/bird) FCR
0·497 0·807 1·630
14·03 0·529 0·819 1·548
14·37
14·24
0·550 0·891 1·641
0·506 0·826 1·634
14·17 0·505 0·794 1·573
a
Residual degrees of freedom were 31, except for TMEn (35). ∗ = P<0·05, NS=P[0·05.
(P<0·05) weight gain and feed intake compared to the 1990 and 1991 harvest year samples. There were no cultivar×harvest year interactions (P>0·05) in growth rate or feed intake although there was an interaction (P<0·05) in the FCR results. The FCR of birds given the 1991 Dean sample was greater than that in 1990 or 1992 (P<0·05) whereas there were no (P>0·05) harvest year differences with the Beaver samples. There were only small differences in the proximate chemical compositions between the six wheat cultivars used in broiler Experiment 1 (Table II). The lower Hagberg falling number of Beaver and Riband compared to other cultivars was expected from national cultivar testing results18. Similarly, the low and high endosperm harness of the Beaver and Dean samples, respectively, was expected (S. Brown, pers. comm.). The differences in water-extract viscosity were also expected from other published information indicating a similar ranking in digesta viscosity between these cultivars19. Brigadier and Beaver had the fastest and slowest rates of starch digestion, respectively. Dean, Brigadier and Rialto had the highest concentration of total NSP, however, Beaver and
Haven had the highest soluble NSP concentration. There were no significant differences (P>0·05) in the determined TME of the wheat samples. The samples of Dean and Beaver obtained from the three different harvest years had some large differences in the rapid tests of wheat quality. Samples from the 1992 harvest had low Hagberg falling number, specific weight and endosperm hardness. The 1992 harvest had a particularly high rainfall in the month (August) during which harvest occurred. Total rainfall for August in 1990, 1991 and 1992 was 37 mm, 25 mm and 127 mm respectively. The total starch contents of the Dean and Beaver samples from the 1992 growing year were lower than those of the samples from the previous two years and there was an increased total NSP concentration although this was mostly due to an increase in the insoluble NSP. The poor harvest conditions in 1992 could possibly have increased the fungal contamination of these wheat samples although mycotoxin contaminations were not measured in the present study. However, national monitoring of fungal disease incidence in the U.K. wheat crop indicated a low disease incidence in 1990, 1991 and 199220. In each of these
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Table III
Comparison of two wheat cultivars in 1990, 1991 and 1992 for wheat characteristics and broiler performance Beaver 1990
1991
Dean 1992
881 110 13
879 97 12
Rapid tests of wheat quality Hagberg falling number (s) Specific weight (kg/hL) Hardness (arbitrary units) Water extract viscosity (cP)
381 74·2 20·3 7·3
221 71·9 13·0 5·8
Polysaccharide characteristics Total starch (g/kg) Amylose: amylopectin Total NSP (g/kg) Insoluble NSP (g/kg) Soluble NSP (g/kg)
640 652 606 0·469 0·490 0·462 103 99 110 73 73 81 30 26 29
In vivo determined metabolisable energy 14·67 TMEn (MJ/kg DM) Broiler growth performance Weight gain (kg/bird) Feed intake (kg/bird) FCR a b
0·382 0·650 1·702
14·72 0·405 0·685 1·691
883 127 13 89 57·7 0 12·7
14·37 0·349 0·597 1·710
Residual degrees of freedom were 31, except for TMEn (35). ∗∗∗=P<0·001, ∗∗=P<0·01, ∗=P<0·05, NS=P[0·05.
1991
1992
Year
Cultivar×year
SEa
Significanceb
SE
Significance
SE
Significance
877 122 13
878 101 12
881 129 13
— — —
— — —
— — —
— — —
— — —
— — —
532 71·9 86·6 4·1
328 72·6 75·4 9·6
218 66·1 56·3 4·8
— — —
— — —
— — —
— — —
— — —
— — —
— — — — —
— — — — —
— — — — —
— — — — —
— — — — —
— — — — —
0·035
NS
0·043
∗∗∗
0·061
∗
0·0078 0·0113 0·0117
∗∗∗ ∗∗ ∗∗∗
0·0096 0·0138 0·0143
∗ ∗ NS
0·0140 0·0195 0·0203
NS NS ∗
636 660 604 0·457 0·472 0·450 110 109 118 74 78 98 26 31 20 14·91 0·437 0·689 1·577
14·58 0·427 0·713 1·670
14·57 0·404 0·662 1·639
S. P. Rose et al.
Proximate nutrient composition Dry matter (g/kg) Crude protein (g/kg) Ether extract (g/kg)
1990
Cultivar
Nutritive value of wheat for chickens
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Table IV Correlation matrix (10df ) between three measures of proximate nutrient composition of 12 wheat samples, four rapid tests of wheat quality and variables of mean growth performance of broiler chickens fed nutritionally complete diets containing these wheat samples. Growth performance was compared in two separate growth experiments, so growth performance data used standardised residuals with growth experiment as a grouping factor Dry matter (DM) 1·000 Crude protein (CP) −0·239 Ether extract (EE) −0·208 Hagberg falling number (HFN) −0·549 Specific weight (SW)a −0·832 Endosperm hardness (Hard) −0·558 Water extract viscosity (Visc) 0·491 Broiler feed intakes (Feed) −0·164 Broiler weight gain (Gain) −0·246 Broiler feed conversion ratio (FCR) 0·260 DM
1·000 0·427 0·060 −0·083 0·220 −0·089 −0·293 −0·222 −0·054 CP
1·000 −0·033 1·000 0·130 0·718 1·000 −0·080 0·718 0·532 1·000 −0·094 −0·528 −0·598 −0·582 1·000 −0·298 0·485 0·430 0·554 −0·326 1·000 −0·340 0·614 0·424 0·743∗−0·561 0·896 1·000 0·139 −0·488 −0·168 −0·624∗ 0·650∗−0·103 −0·527 EE HFN SW Hard Visc Feed Gain
1·000 FCR
a Specific weight data were log transformed before calculation of correlation coefficients. ∗ Indicates a statistically significant (P<0·05) correlation between a single wheat measurement and a broiler growth performance variable.
years, the fungal disease incidence was lower than would be expected to produce levels of toxins, for example deoxynivalenol or zearalenone, that would affect the health or growth performance of poultry21. The differences in water-extract viscosity due to harvest year were more variable although Beaver harvested in 1992 had the highest water-extract viscosity. There was a variety x harvest year interaction in TME with the TME of 1992 Beaver being lower (P<0·05) than that of the 1990 and 1991 Beaver samples but there were no significant differences (P>0·05) between the Dean harvest year samples. Dean samples from the three harvest years had a similar total starch content but a higher amylose: amylopectin ratio and faster rate of starch digestion compared to the Beaver samples. The contents of NSP were similar between the two cultivar samples. A correlation matrix was used to initially compare the relationships between the proximate nutrient analyses plus rapid tests of quality with the growth performance of the broiler chickens (Table IV). For broiler growth performance, the only significant (P<0·05) correlation coefficient occurred with endosperm hardness and water extract viscosity. Both endosperm hardness and water extract viscosity were significantly (P<0·05) correlated to broiler chicken FCR. There was a nonsignificant (P>0·05) correlation between broiler chicken feed intakes and endosperm hardness. The endosperm hardness data tended to be bimodal
because of the very high endosperm hardness of the three Dean samples. However, no transformations of these data were found to improve the normality of its distribution. Multiple linear regression was used to examine the relationship between any of the three proximate nutrient analysis variables and four rapidtests of wheat quality with each of the three variables of broiler growth performance after first fitting a factor for growth experiment. Endosperm hardness was significantly (P<0·05) related to the three growth performance variables (weight gain, feed intake and FCR) [Figs 1(a,b,c)]. Addition of any combination of other variables with endosperm hardness did not (P>0·05) significantly reduce the residual sums of squares of the regression analysis for either of the three growth performance variables. In vitro viscosity was positively (P<0·05) related to the differences in broiler feed conversion ratio. Endosperm hardness and in vitro viscosity of the 12 wheat samples were selected for further study. A preliminary correlation matrix (Table V) followed by a multiple linear regression analysis was used to examine the relationship between endosperm hardness and the detailed polysaccharide characteristics or determined TME of the wheat samples. There was no single characteristic or combination of characteristics that were significantly (P<0·05) related to the variation in endosperm hardness. The in vitro viscosities of the wheat samples were significantly related (P<0·05) to the content of soluble NSPs.
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DISCUSSION The growth performance data from the first experiment confirmed that there were significant 0.52 (a) –1
Weight gain (kg bird )
0.50 0.48 0.46 0.44 0.42 0.40 0.38
0
20 40 60 80 Hardness (arbitrary units)
100
0
20 40 60 80 Hardness (arbitrary units)
100
0
20 40 60 80 Hardness (arbitrary units)
100
0.84
–1
Feed intake (kg bird )
0.82
(b)
0.80 0.78 0.76 0.74 0.72 0.70 0.68 0.66
1.75
Feed conversion ratio
(c) 1.70
1.65
1.60
1.55
1.50
Figure 1 Relationships between hardness of wheat grain fed to chickens and (a) weight gain, (b) feed intake, (c) feed conversion ratio. Data were from two separate growth experiments and a factor for growth experiment has been fitted first.
differences in broiler growth rates when they were fed the six different wheat cultivars. The range of differences due to cultivar samples has been observed in previous studies2,23. The growth rates of the broilers fed Beaver were numerically the lowest and birds fed Brigadier and Dean had growth rates that were 10·7% and 6·4% greater respectively. However, whereas the high growth rates of the birds fed Brigadier could be entirely accounted for by their high feed intakes, the birds fed Dean tended (P>0·05) to have a lower feed conversion ratio. The second broiler experiment confirmed that the birds fed Dean had a 9·6% greater (P<0·001) weight gain compared to those fed Beaver, but with only a 6·8% greater feed intake that again resulted in a lower feed conversion ratio. The data also indicated that the harvest year had an equally large effect on growth performance of the broilers. The wheats from the 1992 harvest year gave broiler growth rates that were 8·4% lower compared to the 1990 and 1991 wheat samples. The poor harvest conditions for this crop also probably contributed to the low specific weight, Hagberg falling number and endosperm hardness, although there was no consistent effect on water-extract viscosity. The correlation matrix (Table IV) indicated that both endosperm hardness and water-extract viscosity were significantly (P<0·05) related to the treatment differences in broiler feed conversion ratio. The difference in feed conversion ratio between broiler chicken flocks kept in intensive management systems is the single most important factor that determines their relative economic efficiency. Endosperm hardness has not previously been considered a major factor that could relate to the nutritional value of wheat for broilers although a study by Salah Uddin et al.22 compared just two wheat samples that were selected to be similar in nutrient composition but differed in their determined endosperm hardness. They found no significant differences in growth performance. However, there is a much greater amount of published evidence in which the growth performance of broilers fed different wheat cultivars have been compared. This data can be re-examined and the cultivars classified as ‘hard’ or ‘soft’ endosperm. Endosperm hardness is primarily determined genetically and there are large consistent differences between different cultivars. Veldman and Vahl23 compared two cultivars and demonstrated a significantly increased growth rate of broilers fed the hard endosperm cultivar. Rose
Nutritive value of wheat for chickens
Table V
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Correlation matrix (10df ) between the endosperm hardness and water extract viscosity of 12 wheat samples and measures of polysaccharide composition and determined metabolisable energy (TME)
Endosperm hardness (Hard) Water extract viscosity (Visc) Total available starch (Starch) Amylose:amylopectin ratio (Am:AmPec) Total non starch polysaccharides (NSP) Soluble NSP (soINSP) Insoluble NSP (insNSP) TME
1·000 −0·582 0·514 −0·081 0·088 −0·567 0·314 −0·212 Hard
1·000 −0·290 −0·125 −0·205 0·730∗ −0·161 −0·002 Visc
1·000 0·310 −0·350 −0·170 −0·193 −0·078 Starch
1·000 −0·880∗∗ −0·205 −0·547 −0·479 Am:AmPec
1·000 0·187 1·000 0·699∗ −0·490 1·000 0·506 0·515 −0·042 NSP soINSP insNSP
1·00 TME
Asterisks indicate statistically significant (∗P<0·05, ∗∗P<0·01) correlations.
et al.24 found that three hard endosperm cultivars tended (P>0·05) to give an improved broiler growth performance compared to three soft endosperm cultivars. Scott et al.25 compared a large number of Western Canadian wheat cultivar samples and observed that the Durum wheat samples (very hard endosperm) and a very hard endosperm (non-Durum) wheat cultivar gave significantly increased broiler chicken growth performance compared to hard red spring cultivars. It thus appears that the relationship between endosperm hardness and the growth performance of broilers may also occur in wheat samples that are grown outside the U.K. Variation in endosperm hardness results in wheat samples having different milling characteristics. Hard endosperm wheat samples result in a high proportion of larger, irregularly-shaped particles in which the starch granules are frequently cleaved. Soft endosperm wheat samples result in a ground wheat sample in which particles sizes are smaller and there are greater proportions of intact starch granules. Cleaved starch granules solubilise quicker than when they are intact, so this may have been a factor in increasing the growth performance of the broilers. A hard endosperm wheat sample may hydrolyse more quickly in the digestive tract and would therefore allow a greater proportion of the available nutrients to be digested in the proximal small intestine and a smaller proportion of nutrients would become substrates for the relatively larger microbial population in the distal small intestine. Higher amounts of microbial fermentation of nutrients would increase the heat increment of digestion and produce greater amounts of volatile fatty acids that are poorly utilised by non-ruminant farm animals. The TMEn assay does not discriminate
between the site or form of energy digestion within the digestive tract, so the lack of a relationship (P<0·05) between TMEn and broiler growth performance is therefore not surprising. Hardness is affected by crop growth and harvest conditions as well as cultivar differences7. The direct measurement of endosperm hardness would therefore also be more accurate than discriminating between cultivars on their expected endosperm hardness and would eliminate the need to segregate feed wheat samples according to their cultivar before delivery to a feed mill. The measurement of endosperm hardness using an NIR technique is rapid, so this test has the potential to be used to discriminate between wheat samples on their arrival at a poultry feed mill. This would allow decisions to be made on the suitability of a wheat batch for inclusion in broiler chicken feeds before the delivery is accepted by the mill. Water-extract viscosity was also related to broiler feed conversion ratio. Measurement of water-extract viscosity requires approximately 30 min so it is less valuable as a measure of nutritional value of wheat samples being received at a feed mill. There was a correlation coefficient of 0·58 (P>0·05) between endosperm hardness and water-extract viscosity so there was no significant (P>0·05) improvement in the prediction of broiler feed conversion ratio by including viscosity with endosperm hardness in a multiple regression analysis. The significant relationship between soluble non-starch polysaccharides and the viscosity of the wheat samples has previously been established26. In conclusion, this study has demonstrated that there are differences in the growth performance of broiler chickens when fed different wheat cultivar samples. The determined endosperm hardness was related (P<0·05) to the weight gain and feed con-
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version ratio of the broiler chickens. The near infra-red spectroscopy technique for determining endosperm hardness has the potential as a rapidtest of nutritional value for wheat samples arriving at poultry feed mills.
13. 14. 15.
REFERENCES 1. Home Grown Cereals Authority. Wheat statistics 1997. HGCA, London. (1997). 2. March, B.E. and Biely, J. Chemical, physical, and nutritional characteristics of different samples of wheat. Canadian Journal of Animal Science 53 (1973) 569–577. 3. Wiseman, J., Nicol, N. and Norton, G. Developments in the nutritional value of wheat for non-ruminants. In ‘Recent Advances in Animal Nutrition 1994’ (P.C. Garnsworthy and D.J.A. Cole, eds), Nottingham University Press, Loughborough, U.K. (1994). 4. Kettlewell, P.S. Agronomy and cereal quality. In ‘Cereal grain quality’ (R.J. Henry and P.S. Kettlewell, eds), Chapman and Hall, London (1996) pp 407–437. 5. Choct, M. and Annison, G. Antinutritive effect of wheat pentosans in broiler-chickens—roles of viscosity and gut microflora. British Poultry Science 33 (1992) 821–834. 6. Scucsne, P.J., Rose, P., Csizmadia, M. and Alder, D. Relationship between the viscosity and the feed value of wheat. Hungarian Journal of Animal Science 48 (1999) 559–567. 7. Anonymous. Determination of the ‘Falling Number’ according to Hagberg-Perten as a measure of the degree of alpha-amylase activity in grain and flour. International Association of Cereal Chemistry, ICC-Standard, No. 107. (1968). 8. Pomeranz, Y. and Williams, P.C. Wheat hardness: its genetic, structural, and biochemical background, measurement, and significance. In ‘Advances in Cereal Science and Technology’ Volume X (Y. Pomeranz, ed.), American Association of Cereal Chemists, St. Paul, Minnesota, pp 471–548. 9. Annison, G. Relationships between levels of soluble nonstarch polysaccharides and the apparent metabolisable energy of wheats assayed in broiler chickens. Journal of Agricultural Food Chemistry 39 (1991) 1252–1256. 10. Rose, S.P. and Bedford, M.R. Relationship between the metabolizable energies of wheat samples and the productive performance of broilers. British Poultry Science 36 (1995) 864–865. 11. Rogel, A.M., Annison, E.F., Bryden, W.L. and Balnave, D. The digestion of wheat-starch in broiler-chickens. Australian Journal of Agricultural Research 38 (1987) 639–649. 12. Stone, B.A. Cereal grain carbohydrates. In ‘Cereal Grain
16. 17. 18. 19.
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Quality’ (R.J. Henry and P.S. Kettlewell, eds), Chapman and Hall, London (1996) pp. 251–288. Association of Official Analytical Chemists. Official Methods of Analysis 16th edition. AOAC, Virginia, U.S.A. (1996). Gibson, T., Solah, V. and McCleary, B. A procedure to measure amylose in cereal starches and flours with concanavalin A. Journal of Cereal Science 25 (1997) 111–119. Englyst, H.N. and Cumming, J.H. Improved method for measurement of dietary fibre as non-starch polysaccharides in plant food. Journal of the Association of Official Analytical Chemists 71 (1988) 808–814. McNab, J.M. and Blair, J.C. Modified assay for true and apparent metabolisable energy based on tube feeding. British Poultry Science 29 (1988) 697–707. National Research Council. Nutrient Requirements of Poultry. 9th edition. National Academy of Science, Washington D.C., U.S.A. (1994). Anon. Recommended Varieties of Cereals 1991. National Institute of Agricultural Botany, Cambridge, U.K. (1991). Waldron, L.A., Rose, S.P. and Kettlewell, P.S. The effects of feeding two wheat varieties from two growing years on the productive performance and digesta viscosity of broiler chickens at three ages. Aspects of Applied Biology, Cereal Quality III 28 (1993) 485–486. Turner, J.E., Jennings, P. and Nicholson, P. Investigation of Fusarium infection and mycotoxin levels in harvested wheat grain (1998). HGCA Project Report No. 207. HGCA, London (1999). D’Mello, J.P.F., Placinta, C.M. and Macdonald, A.M.C. Fusarium mycotoxins: a review of global implications for animal health, welfare and productivity. Animal Feed Science and Technology 80 (1999) 183–205. Salah Uddin, M., Rose, S.P., Hiscock, T.A. and Bonnet, S. A comparison of the energy availability for chickens of ground and whole grain samples of two wheat varieties. British Poultry Science 37 (1996) 347–357. Veldman, A. and Vahl, H.A. Xylanase in broiler diets with differences in characteristics and content of wheat. British Poultry Science 35 (1994) 537–550. Rose, S.P., Kettlewell, P.S., Reynolds, S.M. and Watts, R.M. The nutritive value of different wheat varieties for poultry. Proceedings of the Nutrition Society 52 (1993) 206A. Scott, T.A., Silversides, F.G., Classen, H.L., Swift, M.L. and Bedford, M.R. Effect of cultivar and environment on the feeding value of Western Canadian wheat and barley samples with and without enzyme supplementation. Canadian Journal of Animal Science 78 (1998) 649–656. Dusel, G., Kluge, H., Gla¨ ser, K., Simon, O., Hartmann, G., Lengerken, J.v. and Jeroch, H. An investigation into the variability of extract viscosity of wheat-relationship with the content of non-starch-polysaccharide fraction and metabolisable energy for broiler chickens. Archives of Animal Nutrition 50 (1997) 121–135.
Rapid Tests of Wheat Nutritive Value for Growing Chickens S. P. Rose∗‡, L. A. Tucker∗§, P. S. Kettlewell† and J. D. A. Collier∗ Harper Adams University College, ∗National Institute of Poultry Husbandry; †Crop and Environment Research Centre, Edgmond, Newport, Shropshire TF10 8NB U.K. Received 25 July 2000
ABSTRACT Two series of broiler chicken feeding experiments quantified the differences in growth performance of broiler chickens fed either six different U.K. wheat cultivars from one harvest year or six wheat samples that comprised two cultivars (Dean and Beaver) each grown in three harvest years. Differences in broiler growth performance were compared to four rapid tests of wheat quality (specific weight, Hagberg falling number, water-extract viscosity and endosperm hardness) and the determined true metabolisable energy. Broilers fed the cultivar Dean had higher (P<0·001) weight gains and lower (P<0·05) feed conversion ratios compared to those fed Beaver. Samples from a harvest year (1992) in which there was high rainfall in the month during which harvest occurred resulted in lower (P<0·05) broiler feed conversion ratios. Endosperm hardness and water-extract viscosity were both linearly related (P<0·05) to differences in broiler feed conversion ratios but there was no (P>0·05) reduction in unaccountable variation from including both variables in a multiple regression analysis. The measurement of endosperm hardness by near infra-red spectroscopy is rapid and has the potential to be used to discriminate nutritive value between wheat samples on their arrival at poultry feed mills. 2001 Academic Press
Keywords: wheat, nutrition, chickens, hardness, viscosity.
INTRODUCTION Proprietary broiler chicken feeds contain up to 70% by weight of cereals. The choice between cereals primarily depends upon their relative price per unit of available energy, and wheat is the main cereal used in broiler chicken feeds in most northern European countries. Within the U.K. for example, 5·4 million tonnes of home-produced wheat are used in animal feeds1 and the broiler chicken industry (750 million birds per annum) uses approximately 20% of this total. Wheat will typically provide 55% of the metabolisable energy
‡ Corresponding author. E-mail: [email protected] § Current Address: Finnfeeds International Ltd, Marlborough, SN8 1AA, U.K. 0733–5210/01/050181+10 $35.00/0
(ME) and 35% of the protein supplied in a proprietary wheat-based broiler feed. Economically efficient broiler feeds must achieve a low feed conversion ratio (FCR) (kg feed eaten per kg of weight gain) but also allow the birds to maximise their rates of weight gain. There is evidence that the FCRs and growth rates of broiler chickens are affected by the use of different wheat samples2. The poultry feed industry needs reliable tests to indicate the nutritional value of the different wheat samples that they receive at their mills. Commercial feed mills may determine the content of moisture, crude protein and ether extract by near- infra red spectroscopy (NIR) on incoming grain samples, however, none of these proximate nutrients are good indicators of the resulting broiler chicken growth performance. Specific 2001 Academic Press
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weight (test weight) of the sample is another rapid measurement that may be used to indicate nutritional quality of a wheat sample. However, there is also a poor relationship between specific weight of wheat samples and the growth performance of chickens3. The specific weight of wheat samples can be affected by cultivar, agronomic and environmental factors that may not also affect the nutritional value of the wheat sample4. Polysaccharides comprise up to 80% of wheat grain, thus variation in their composition could have major effects on the nutritional value of a wheat sample. Tests that measure different characteristics of the polysaccharide content of wheat could possibly relate to differences in nutritional value. Three rapid tests are currently available that meet this criterion. Wheat viscosity is related to the content of soluble non-starch polysaccharides in wheat5 and is linearly related to the differences in in vivo digesta viscosity when wheat samples are fed to broiler chickens6. Hagberg falling number is related to the reciprocal of alpha-amylase activity in wheat grains7 and endosperm hardness is related to the milling characteristics and subsequent rate of gelatinisation of starch granules8. Total starch and non-starch polysaccharides are correlated with the metabolisable energy (ME) content of wheat9, but variation in the determined ME between wheat samples may not be a good indicator of the growth performance of broiler chickens given the samples in nutritionally complete diets. A review of published experiments established that differences in broiler FCRs and growth rates due to feeding different wheat samples were not correlated with differences in the determined ME10. There is a lack of information on the variation in the characteristics of the wheat starch and its nutritional value for poultry. There is little variation in the digestibility of wheat starch when fed to chickens but chemical or structural characteristics may affect the efficiency of utilisation of the digestible starch11. Wheat starches are a mixture of amylose and amylopectin and the ratio of these two components can vary12. Variation in starch granule characteristics may result in different rates of starch digestion that affect the efficiency of utilisation of the digestible starch. In summary, there is a lack of information that indicates if laboratory tests are related to broiler chicken growth performance when wheat samples are fed in nutritionally complete diets. Differences in growth performance have been observed between
different wheat cultivars and the same cultivars grown in different locations or in different harvest years. A laboratory test needs to detect the cultivar and environmental effects and needs to provide results quickly to allow rapid throughput of wheat samples through commercial poultry feed mills. The present study had four main objectives that involved two series of broiler chicken feeding experiments. The main objectives were: (1) to quantify the differences in growth performance of broiler chickens fed nutritionally complete diets containing one of six different U.K. wheat cultivars from one harvest; (2) to quantify the differences in growth performance of broiler chickens fed nutritionally complete diets containing one of six wheat samples that comprised two cultivars (Dean and Beaver) each grown in three harvest years; (3) to relate broiler chicken growth performance (growth rate, feed intakes and feed conversion ratio) to the proximate nutrient composition and four rapid tests of wheat quality (specific weight, water-extract viscosity, Hagberg falling number and endosperm hardness); (4) to relate any rapid test that was selected to differences in the polysaccharide content of the wheat (non-starch polysaccharides, available starch and amylose: amylopectin ratio) and the determined true ME.
EXPERIMENTAL Wheat samples For Experiment 1, the cultivars Beaver, Brigadier, Dean, Riband, Haven and Rialto were grown in the 1994 harvest year in three randomised blocks at Harper Adams College in Shropshire. Initial inspection of the broiler chicken experiment data indicated that there were significant differences in broiler growth performance due to cultivar. Two cultivars that gave significantly different growth performance were selected and further samples of these two cultivars were sourced that had been grown in different harvest years. Samples of Dean and Beaver were obtained that had been grown in three randomised blocks in each of the three harvest years 1990, 1991 and 1992. The cultivars were grown at two sites (Escrick Park and Hornsea, Yorkshire, U.K.) in 1990 and at Harper Adams College in the 1991 and 1992 harvest years. The crops were managed according to typical U.K. commercial wheat production methods with applications of fertiliser, herbicide, fungicide,
Nutritive value of wheat for chickens
insecticide and growth regulator as necessary to optimise yield. Equal amounts of grain of each cultivar from the three randomised blocks was pooled to give one sample for milling from each cultivar in each year. Grain from the two sites in 1990 was pooled. In addition, wheat samples were mixed in a horizontal mixer before hammer milling using a 2-mm screen. Stored grain from all years was freshly milled for each feeding experiment. Wheat grain analyses Dry matter, crude protein, crude fibre, ether extract and Hagberg falling number were determined using AOAC13 procedure numbers 925·10, 984·13, 962·09, 920·39 and 976·13 respectively. Endosperm hardness was measured following the AOAC procedure number 983·03 using an Oxford QN 1000 near infra-red reflectance (NIR) analyser (Oxford Instruments, Oxford, U.K.) with the 1992 Beaver sample used as the zero calibration point. The specific weight of the grain was measured using a chondrometer. The water extract viscosity was determined by soaking a 2-g sample of wheat in 4 mL of water at 30 °C for 30 min. The sample was centrifuged at 10 000×g for 2 min and the viscosity of the supernatant was measured in a rotating cone and cup viscometer (model DVII+LV, Brookfield, Stroughton, MA, U.S.A.). The total starch, amylose and amylopectin content of the wheat samples was determined using a procedure devised by Gibson et al.14 (amylose/ amylopectin assay kit, Megazyme International Ireland Ltd., Bray, Ireland). Total non-starch polysaccharide (NSP) concentration was measured using an enzymatic technique involving hydrolysis with amylase, pullulanase and pancreatin15 (Englyst Fiberzym kit for colorimetry, Dunn Nutrition Centre, Cambridge, U.K.). The total NSP concentration was further subdivided into the soluble and insoluble fractions. Metabolisable energy determinations Nitrogen-corrected true metabolisable energy (TMEn) concentrations were determined. The experimental protocol followed, with some minor alterations, a previously published technique16. A flock of 24 adult ISA Brown cockerels with a mean body weight of 3·2 kg were housed singly in cages kept in an environmentally controlled room. The
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TMEn determination involved deducting from a bird’s gross energy intake the total gross energy produced in the excreta in the subsequent 48 h. Access to feed was withdrawn from the previously ad libitum fed cockerels and after 24 h they were given a sucrose solution that provided 35 g of sucrose. After a further 24 h each cockerel was given 50 g of a ground wheat sample that was intubated directly into the bird’s crop. The total amount of gross energy excreted was corrected for endogenous energy excretion. Endogenous energy excretion was estimated at each determination by feeding 35 g of sucrose in solution to three of the cockerels, in replacement for the test wheat sample. Data from all birds was nitrogen-corrected to adjust for the nitrogen in the excreta that was derived from body protein catabolism. A correction factor of 32MJ was applied per kg of nitrogen excreted that was in excess of the amount fed. All excreta samples were dried at 60 °C immediately following the collection period. A total of nine replicate TME determinations were made for each wheat sample. Gross energy determinations of the wheat and excreta samples were made in an adiabatic bomb calorimeter (Parr-1755, Parr Instruments Company, Moline, IL, U.S.A.).
Chicken growth comparisons Two separate experiments were performed to examine differences in the growth performance of broiler chickens when fed diets containing 700 g/ kg of each of the wheat samples. Both experiments compared the growth performance of the broilers fed six wheat samples. Experiment 1 compared the six wheat cultivar samples from the 1994 harvest year. Experiment 2 compared the two wheat cultivars, Dean and Beaver, grown in the 1990, 1991 and 1992 harvest years. Identical procedures were used for the two experiments except that they were conducted at different times using different batches of broiler chickens. The experimental feeds were produced by mixing 700 g/kg of each of the ground wheat samples with other feed ingredients (Table I). No adjustment was made to account for the small differences in nutrient compositions of the wheat samples. The overall nutrient composition of the final diets was formulated to exceed the NRC17 specified nutrient requirements of this age of broiler chicken by a minimum of 15% for all essential amino acids and fatty acids. Any possible
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Table I The ingredient composition and calculated composition of the diets in two broiler chicken growth experiments Ingredient
Proportion (g/kg)
Experimental wheat (ground) Full fat soya bean (micronised) Fish meal Meat and bone meal -Methionine Vitamin and trace mineral premixa
700 155 97·5 25 2·5 20
Calculated nutrient composition Metabolisable energy (MJ/kg) Crude protein (g/kg) Lysine (g/kg) Methionine plus cystine (g/kg) Calcium (g/kg) Phosphorus (g/kg) Sodium (g/kg)
12·3 215 12 9 11 7 3
a Proprietary supplement that provided vitamins and trace elements as specified by NRC17. In addition, the premix provided 6·25 mg/kg of an anticoccidial drug (amprolium) and 0·4 mg/kg and 0·5 mg/kg respectively of two antimicrobial growth promoters (ethopabate and avoparcin).
variation in amino acid or fatty acid availability that occurred between the wheat samples would therefore have had little, or no, effect on the growth performance of the chickens. There are presently no reliable rapid methods that detect nutrient availability in wheat grains, so the procedure of using fixed wheat inclusion rates is relevant to the commercial poultry feed industry which would deal with different batches of wheat in a similar manner. Ninety-six day-old male Ross hybrid broiler chickens were fed a proprietary broiler starter feed and kept in a littered floor pen for 7 d. The birds were then randomly allocated to 48 cages with two birds being placed in each cage. The cages were 0·3 m high and had a floor area of 0·09 m2. The birds were given ad libitum access to feed and water from troughs attached to the front of the cages. The cages were kept in a controlled environment room that was initially kept at 30 °C and gradually reduced to 25 °C over the 14 d experimental period. Thirty minutes of darkness were given each 24 h. There were two sets of cages within the room and each set had six cages on each of four tiers. Each cage of birds within a sixcage tier was randomly given one of the experimental diets. The birds were given the diets for 14 d and feed intake and weight gains of the birds were measured.
Statistical analysis The differences between the wheat samples within a broiler growth experiment were compared by a randomised block analysis of variance using cage tiers as blocks. Comparisons of the samples from the 1990, 1991 and 1992 harvest years used a factorial analysis (cultivar×growing season) to compare main treatment effects and their interactions. Differences in TMEn between the wheat samples were compared by a randomised block analysis using the time repetitions as the blocking factor. The relationship between the growth performance of the broiler chickens and the proximate chemical composition and the four rapid tests of wheat quality were first examined by calculating a correlation coefficient matrix and, second, examined by a multiple linear regression technique. The two broiler growth experiments were used as a blocking factor. The data for specific weight were found to be skewed, therefore they were natural log transformed before the statistical analysis was performed. The relationship between any of the four rapid tests of wheat quality and the determined polysaccharide composition of the wheat samples was examined by a multiple linear regression technique. No blocking factors were necessary. RESULTS There were significant differences (P<0·05) in growth due to the six different wheat cultivar samples in Experiment 1. The growth of the chickens fed Brigadier was greater (P<0·05) than those fed Beaver, although the FCR of these two treatment groups was similar. Both the growth and FCR of the birds given Dean tended (P>0·05) to be higher than those fed Beaver. Samples of both Dean and Beaver cultivars could be obtained from stored wheat from the 1990, 1991 and 1992 harvest years, so experimental comparisons were continued with these six wheat samples (two cultivars×three harvest years). The results of the second broiler experiment confirmed that the birds fed the Dean cultivar samples had significantly greater weight gain (P<0·001) and feed intake (P<0·01) than those fed Beaver samples. The experiment also demonstrated that the growing season affected broiler growth performance. The birds given samples from the 1992 harvest year had significantly lower
Nutritive value of wheat for chickens
Table II
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Comparison of six cultivars grown in 1994 for wheat characteristics and broiler performance Beaver
Dean Brigadier Rialto
Riband
Haven
SEa
Significance
Proximate nutrient composition Dry matter (g/kg) Crude protein (g/kg) Ether extract (g/kg)
872 128 13
870 118 11
873 127 13
873 132 14
871 118 15
871 121 14
— — —
— — —
Rapid tests of wheat quality Hagberg falling number (s) Specific weight (kg/hL) Hardness (arbitrary units) Water-extract viscosity (cP)
322 76·4 32·0 7·0
440 77·8 95·2 4·1
380 77·1 79·9 5·2
403 76·9 85·5 5·7
291 77·4 58·9 3·4
400 77·3 46·4 8·2
— — — —
— — — —
Polysaccharide characteristics Total starch (g/kg) Amylose: amylopectin Total NSP (g/kg) Insoluble NSP (g/kg) Soluble NSP (g/kg)
640 662 659 660 631 629 0·492 0·466 0·481 0·491 0·506 0·500 98 101 101 105 92 94 73 84 81 87 74 68 25 17 20 18 18 26
— — — — —
— — — — —
13·98
0·462
NS
0·503 0·822 1·637
0·0211 0·0313 0·0561
∗ NS NS
In vivo determined metabolisable energy TMEn (MJ/kg DM) 14·51 Broiler growth performance Weight gain (kg/bird) Feed intake (kg/bird) FCR
0·497 0·807 1·630
14·03 0·529 0·819 1·548
14·37
14·24
0·550 0·891 1·641
0·506 0·826 1·634
14·17 0·505 0·794 1·573
a
Residual degrees of freedom were 31, except for TMEn (35). ∗ = P<0·05, NS=P[0·05.
(P<0·05) weight gain and feed intake compared to the 1990 and 1991 harvest year samples. There were no cultivar×harvest year interactions (P>0·05) in growth rate or feed intake although there was an interaction (P<0·05) in the FCR results. The FCR of birds given the 1991 Dean sample was greater than that in 1990 or 1992 (P<0·05) whereas there were no (P>0·05) harvest year differences with the Beaver samples. There were only small differences in the proximate chemical compositions between the six wheat cultivars used in broiler Experiment 1 (Table II). The lower Hagberg falling number of Beaver and Riband compared to other cultivars was expected from national cultivar testing results18. Similarly, the low and high endosperm harness of the Beaver and Dean samples, respectively, was expected (S. Brown, pers. comm.). The differences in water-extract viscosity were also expected from other published information indicating a similar ranking in digesta viscosity between these cultivars19. Brigadier and Beaver had the fastest and slowest rates of starch digestion, respectively. Dean, Brigadier and Rialto had the highest concentration of total NSP, however, Beaver and
Haven had the highest soluble NSP concentration. There were no significant differences (P>0·05) in the determined TME of the wheat samples. The samples of Dean and Beaver obtained from the three different harvest years had some large differences in the rapid tests of wheat quality. Samples from the 1992 harvest had low Hagberg falling number, specific weight and endosperm hardness. The 1992 harvest had a particularly high rainfall in the month (August) during which harvest occurred. Total rainfall for August in 1990, 1991 and 1992 was 37 mm, 25 mm and 127 mm respectively. The total starch contents of the Dean and Beaver samples from the 1992 growing year were lower than those of the samples from the previous two years and there was an increased total NSP concentration although this was mostly due to an increase in the insoluble NSP. The poor harvest conditions in 1992 could possibly have increased the fungal contamination of these wheat samples although mycotoxin contaminations were not measured in the present study. However, national monitoring of fungal disease incidence in the U.K. wheat crop indicated a low disease incidence in 1990, 1991 and 199220. In each of these
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Table III
Comparison of two wheat cultivars in 1990, 1991 and 1992 for wheat characteristics and broiler performance Beaver 1990
1991
Dean 1992
881 110 13
879 97 12
Rapid tests of wheat quality Hagberg falling number (s) Specific weight (kg/hL) Hardness (arbitrary units) Water extract viscosity (cP)
381 74·2 20·3 7·3
221 71·9 13·0 5·8
Polysaccharide characteristics Total starch (g/kg) Amylose: amylopectin Total NSP (g/kg) Insoluble NSP (g/kg) Soluble NSP (g/kg)
640 652 606 0·469 0·490 0·462 103 99 110 73 73 81 30 26 29
In vivo determined metabolisable energy 14·67 TMEn (MJ/kg DM) Broiler growth performance Weight gain (kg/bird) Feed intake (kg/bird) FCR a b
0·382 0·650 1·702
14·72 0·405 0·685 1·691
883 127 13 89 57·7 0 12·7
14·37 0·349 0·597 1·710
Residual degrees of freedom were 31, except for TMEn (35). ∗∗∗=P<0·001, ∗∗=P<0·01, ∗=P<0·05, NS=P[0·05.
1991
1992
Year
Cultivar×year
SEa
Significanceb
SE
Significance
SE
Significance
877 122 13
878 101 12
881 129 13
— — —
— — —
— — —
— — —
— — —
— — —
532 71·9 86·6 4·1
328 72·6 75·4 9·6
218 66·1 56·3 4·8
— — —
— — —
— — —
— — —
— — —
— — —
— — — — —
— — — — —
— — — — —
— — — — —
— — — — —
— — — — —
0·035
NS
0·043
∗∗∗
0·061
∗
0·0078 0·0113 0·0117
∗∗∗ ∗∗ ∗∗∗
0·0096 0·0138 0·0143
∗ ∗ NS
0·0140 0·0195 0·0203
NS NS ∗
636 660 604 0·457 0·472 0·450 110 109 118 74 78 98 26 31 20 14·91 0·437 0·689 1·577
14·58 0·427 0·713 1·670
14·57 0·404 0·662 1·639
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Proximate nutrient composition Dry matter (g/kg) Crude protein (g/kg) Ether extract (g/kg)
1990
Cultivar
Nutritive value of wheat for chickens
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Table IV Correlation matrix (10df ) between three measures of proximate nutrient composition of 12 wheat samples, four rapid tests of wheat quality and variables of mean growth performance of broiler chickens fed nutritionally complete diets containing these wheat samples. Growth performance was compared in two separate growth experiments, so growth performance data used standardised residuals with growth experiment as a grouping factor Dry matter (DM) 1·000 Crude protein (CP) −0·239 Ether extract (EE) −0·208 Hagberg falling number (HFN) −0·549 Specific weight (SW)a −0·832 Endosperm hardness (Hard) −0·558 Water extract viscosity (Visc) 0·491 Broiler feed intakes (Feed) −0·164 Broiler weight gain (Gain) −0·246 Broiler feed conversion ratio (FCR) 0·260 DM
1·000 0·427 0·060 −0·083 0·220 −0·089 −0·293 −0·222 −0·054 CP
1·000 −0·033 1·000 0·130 0·718 1·000 −0·080 0·718 0·532 1·000 −0·094 −0·528 −0·598 −0·582 1·000 −0·298 0·485 0·430 0·554 −0·326 1·000 −0·340 0·614 0·424 0·743∗−0·561 0·896 1·000 0·139 −0·488 −0·168 −0·624∗ 0·650∗−0·103 −0·527 EE HFN SW Hard Visc Feed Gain
1·000 FCR
a Specific weight data were log transformed before calculation of correlation coefficients. ∗ Indicates a statistically significant (P<0·05) correlation between a single wheat measurement and a broiler growth performance variable.
years, the fungal disease incidence was lower than would be expected to produce levels of toxins, for example deoxynivalenol or zearalenone, that would affect the health or growth performance of poultry21. The differences in water-extract viscosity due to harvest year were more variable although Beaver harvested in 1992 had the highest water-extract viscosity. There was a variety x harvest year interaction in TME with the TME of 1992 Beaver being lower (P<0·05) than that of the 1990 and 1991 Beaver samples but there were no significant differences (P>0·05) between the Dean harvest year samples. Dean samples from the three harvest years had a similar total starch content but a higher amylose: amylopectin ratio and faster rate of starch digestion compared to the Beaver samples. The contents of NSP were similar between the two cultivar samples. A correlation matrix was used to initially compare the relationships between the proximate nutrient analyses plus rapid tests of quality with the growth performance of the broiler chickens (Table IV). For broiler growth performance, the only significant (P<0·05) correlation coefficient occurred with endosperm hardness and water extract viscosity. Both endosperm hardness and water extract viscosity were significantly (P<0·05) correlated to broiler chicken FCR. There was a nonsignificant (P>0·05) correlation between broiler chicken feed intakes and endosperm hardness. The endosperm hardness data tended to be bimodal
because of the very high endosperm hardness of the three Dean samples. However, no transformations of these data were found to improve the normality of its distribution. Multiple linear regression was used to examine the relationship between any of the three proximate nutrient analysis variables and four rapidtests of wheat quality with each of the three variables of broiler growth performance after first fitting a factor for growth experiment. Endosperm hardness was significantly (P<0·05) related to the three growth performance variables (weight gain, feed intake and FCR) [Figs 1(a,b,c)]. Addition of any combination of other variables with endosperm hardness did not (P>0·05) significantly reduce the residual sums of squares of the regression analysis for either of the three growth performance variables. In vitro viscosity was positively (P<0·05) related to the differences in broiler feed conversion ratio. Endosperm hardness and in vitro viscosity of the 12 wheat samples were selected for further study. A preliminary correlation matrix (Table V) followed by a multiple linear regression analysis was used to examine the relationship between endosperm hardness and the detailed polysaccharide characteristics or determined TME of the wheat samples. There was no single characteristic or combination of characteristics that were significantly (P<0·05) related to the variation in endosperm hardness. The in vitro viscosities of the wheat samples were significantly related (P<0·05) to the content of soluble NSPs.
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DISCUSSION The growth performance data from the first experiment confirmed that there were significant 0.52 (a) –1
Weight gain (kg bird )
0.50 0.48 0.46 0.44 0.42 0.40 0.38
0
20 40 60 80 Hardness (arbitrary units)
100
0
20 40 60 80 Hardness (arbitrary units)
100
0
20 40 60 80 Hardness (arbitrary units)
100
0.84
–1
Feed intake (kg bird )
0.82
(b)
0.80 0.78 0.76 0.74 0.72 0.70 0.68 0.66
1.75
Feed conversion ratio
(c) 1.70
1.65
1.60
1.55
1.50
Figure 1 Relationships between hardness of wheat grain fed to chickens and (a) weight gain, (b) feed intake, (c) feed conversion ratio. Data were from two separate growth experiments and a factor for growth experiment has been fitted first.
differences in broiler growth rates when they were fed the six different wheat cultivars. The range of differences due to cultivar samples has been observed in previous studies2,23. The growth rates of the broilers fed Beaver were numerically the lowest and birds fed Brigadier and Dean had growth rates that were 10·7% and 6·4% greater respectively. However, whereas the high growth rates of the birds fed Brigadier could be entirely accounted for by their high feed intakes, the birds fed Dean tended (P>0·05) to have a lower feed conversion ratio. The second broiler experiment confirmed that the birds fed Dean had a 9·6% greater (P<0·001) weight gain compared to those fed Beaver, but with only a 6·8% greater feed intake that again resulted in a lower feed conversion ratio. The data also indicated that the harvest year had an equally large effect on growth performance of the broilers. The wheats from the 1992 harvest year gave broiler growth rates that were 8·4% lower compared to the 1990 and 1991 wheat samples. The poor harvest conditions for this crop also probably contributed to the low specific weight, Hagberg falling number and endosperm hardness, although there was no consistent effect on water-extract viscosity. The correlation matrix (Table IV) indicated that both endosperm hardness and water-extract viscosity were significantly (P<0·05) related to the treatment differences in broiler feed conversion ratio. The difference in feed conversion ratio between broiler chicken flocks kept in intensive management systems is the single most important factor that determines their relative economic efficiency. Endosperm hardness has not previously been considered a major factor that could relate to the nutritional value of wheat for broilers although a study by Salah Uddin et al.22 compared just two wheat samples that were selected to be similar in nutrient composition but differed in their determined endosperm hardness. They found no significant differences in growth performance. However, there is a much greater amount of published evidence in which the growth performance of broilers fed different wheat cultivars have been compared. This data can be re-examined and the cultivars classified as ‘hard’ or ‘soft’ endosperm. Endosperm hardness is primarily determined genetically and there are large consistent differences between different cultivars. Veldman and Vahl23 compared two cultivars and demonstrated a significantly increased growth rate of broilers fed the hard endosperm cultivar. Rose
Nutritive value of wheat for chickens
Table V
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Correlation matrix (10df ) between the endosperm hardness and water extract viscosity of 12 wheat samples and measures of polysaccharide composition and determined metabolisable energy (TME)
Endosperm hardness (Hard) Water extract viscosity (Visc) Total available starch (Starch) Amylose:amylopectin ratio (Am:AmPec) Total non starch polysaccharides (NSP) Soluble NSP (soINSP) Insoluble NSP (insNSP) TME
1·000 −0·582 0·514 −0·081 0·088 −0·567 0·314 −0·212 Hard
1·000 −0·290 −0·125 −0·205 0·730∗ −0·161 −0·002 Visc
1·000 0·310 −0·350 −0·170 −0·193 −0·078 Starch
1·000 −0·880∗∗ −0·205 −0·547 −0·479 Am:AmPec
1·000 0·187 1·000 0·699∗ −0·490 1·000 0·506 0·515 −0·042 NSP soINSP insNSP
1·00 TME
Asterisks indicate statistically significant (∗P<0·05, ∗∗P<0·01) correlations.
et al.24 found that three hard endosperm cultivars tended (P>0·05) to give an improved broiler growth performance compared to three soft endosperm cultivars. Scott et al.25 compared a large number of Western Canadian wheat cultivar samples and observed that the Durum wheat samples (very hard endosperm) and a very hard endosperm (non-Durum) wheat cultivar gave significantly increased broiler chicken growth performance compared to hard red spring cultivars. It thus appears that the relationship between endosperm hardness and the growth performance of broilers may also occur in wheat samples that are grown outside the U.K. Variation in endosperm hardness results in wheat samples having different milling characteristics. Hard endosperm wheat samples result in a high proportion of larger, irregularly-shaped particles in which the starch granules are frequently cleaved. Soft endosperm wheat samples result in a ground wheat sample in which particles sizes are smaller and there are greater proportions of intact starch granules. Cleaved starch granules solubilise quicker than when they are intact, so this may have been a factor in increasing the growth performance of the broilers. A hard endosperm wheat sample may hydrolyse more quickly in the digestive tract and would therefore allow a greater proportion of the available nutrients to be digested in the proximal small intestine and a smaller proportion of nutrients would become substrates for the relatively larger microbial population in the distal small intestine. Higher amounts of microbial fermentation of nutrients would increase the heat increment of digestion and produce greater amounts of volatile fatty acids that are poorly utilised by non-ruminant farm animals. The TMEn assay does not discriminate
between the site or form of energy digestion within the digestive tract, so the lack of a relationship (P<0·05) between TMEn and broiler growth performance is therefore not surprising. Hardness is affected by crop growth and harvest conditions as well as cultivar differences7. The direct measurement of endosperm hardness would therefore also be more accurate than discriminating between cultivars on their expected endosperm hardness and would eliminate the need to segregate feed wheat samples according to their cultivar before delivery to a feed mill. The measurement of endosperm hardness using an NIR technique is rapid, so this test has the potential to be used to discriminate between wheat samples on their arrival at a poultry feed mill. This would allow decisions to be made on the suitability of a wheat batch for inclusion in broiler chicken feeds before the delivery is accepted by the mill. Water-extract viscosity was also related to broiler feed conversion ratio. Measurement of water-extract viscosity requires approximately 30 min so it is less valuable as a measure of nutritional value of wheat samples being received at a feed mill. There was a correlation coefficient of 0·58 (P>0·05) between endosperm hardness and water-extract viscosity so there was no significant (P>0·05) improvement in the prediction of broiler feed conversion ratio by including viscosity with endosperm hardness in a multiple regression analysis. The significant relationship between soluble non-starch polysaccharides and the viscosity of the wheat samples has previously been established26. In conclusion, this study has demonstrated that there are differences in the growth performance of broiler chickens when fed different wheat cultivar samples. The determined endosperm hardness was related (P<0·05) to the weight gain and feed con-
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version ratio of the broiler chickens. The near infra-red spectroscopy technique for determining endosperm hardness has the potential as a rapidtest of nutritional value for wheat samples arriving at poultry feed mills.
13. 14. 15.
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