Key words: Metabolizable energy, performance, wheat, barley, feed enzymes

Transcription

1 Prediction of the performance of broiler chicks from apparent metabolizable energy and protein digestibility values obtained using a broiler chick bioassay 1 T. A. Scott 1, F. G. Silversides 2, H. L. Classen 3, M. L. Swift 4, and M. R. Bedford 5 1 Pacific Agri-Food Research Centre, P.O. Box 1000, Agassiz, British Columbia, Canada V0M 1A0, ScottTA@em.agr.ca; East Road, Denman Island, British Columbia, Canada V0R 1T0; 3 Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5B5; 4 Pro-Form Feeds, P.O. Box 1000, Chilliwack, British Columbia, Canada V2P 6J6; 5 Finnfeeds International, Box 777, Marlborough, Wiltshire, United Kingdom SN8 1XN. Agriculture and Agri-Food Canada contribution no. 576, received 8 May 1998, accepted 22 December Scott, T. A., Silversides, F. G., Classen, H. L., Swift, M. L. and Bedford, M. R Prediction of the performance of broiler chicks from apparent metabolizable energy and protein digestibility values obtained using a broiler chick bioassay. Can J. Anim. Sci. 79: Samples of wheat (54) and barley (87) were included in a series of broiler chick bioassays. For each cereal, fed at 80% of a basal diet with or without enzyme, apparent metabolizable energy (AME), retained nitrogen, digesta viscosity, excreta dry matter (DM), and broiler performance (feed intake, body weight [BW] gain, and feed conversion) were measured. Correlation coefficients were calculated between the predictor and the performance variables, separated according to whether or not the diets included feed enzymes. Some correlations between measures of AME and BW, feed efficiency, and to a lesser degree feed intake were significant, but none were high. The correlation coefficients were higher when feeds were not supplemented with an enzyme because enzyme supplementation reduced the variation in both AME and performance by reducing the antinutritive effects of non-starch polysaccharides (NSP). Including a measure of voluntary intake in AME (AME level multiplied by feed intake) resulted in higher correlations with performance. Evaluation of the feeding value of wheat and barley by researchers or the feed industry will require the determination of available energy and the NSP contents. Key words: Metabolizable energy, performance, wheat, barley, feed enzymes Scott, T. A., Silversides, F. G., Classen, H. L., Swift, M. L. et Bedford, M. R Prédiction de la performance des poulets à griller à partir de l énergie métababolisable apparente et de le rétention de protéine obtenues dans un essai biologique pour les poulets à griller. Can J. Anim. Sci. 79: Des échantillons de blé (54) et d orge (87) ont été inclus dans une série d essais biologiques pour des jeunes poulets à griller. Pour chacune des céréales, inclues à 80% à une diète de base avec ou sans enzyme, l enérgie métabolisante apparente (AME), l azote digéré, la viscosité intestinale, la matiére sèche de l excrément et la performance des poussins (consommation, augmentation de poids corporel, croissance et indice de conversion alimentaire) ont été mesurés. Des coefficients de corrélation ont été calculés entre les variables de prédiction et les variables de réponses, séparés selon l inclusion des enzymes dans les rations. Quelques coefficients de corrélation entre des mesures d AME et poids corporel, d efficacité alimentaire, et à moindre degré de consommation ont été significatifs mais aucun n a été élevé. Les coefficients de corrélation ont été plus elevés lorsque la diète ne contenait pas d enzyme parce que la supplémentation réduisait la variation dans l AME et la perforamance en diminuant les effets antinutritifs des NSP insolubles. L inclusion d une mesure de consommation volontaire avec l AME (AME multipliée par consommation) a donné des corrélations plus élevées avec la performance. L évaluation de la valeur alimentaire de blé et de l orge par les chercheurs et par l industrie nécessitera la détermination des niveaux d enérgie disponible et de NSP. Mots clés: Enérgie metabolisable, performance, blé, orge, enzymes alimentaires Cereals make up the major part of a poultry diet and are the primary source of feed energy. Ensuring sufficient energy and balancing the energy-to-protein ratio are fundamental principles of feed formulation (Classen and Stevens 1995), and in theory birds adjust their feed intake to obtain a constant energy intake (Leeson et al. 1996). The poultry feed industry uses published values (National Research Council [NRC] 1994) of the energy content of feedstuffs for feed formulation. However, the energy that the bird obtains from a cereal for metabolic processes (AME) is variable and depends on the energy contained, its availability to the bird, and the presence or concentration of antinutritive compounds such as soluble NSP. The relation of AME in the 59 cereal to bird performance is also affected by such factors as consumption levels, nutritional interactions, and the bird s genetics and environment. Variation in AME content between samples of some cereals, including barley and wheat, is due partly to differences in soluble-nsp content. NSP are contained primarily in the endosperm walls of the cereal grain, and the level depends on genetics and the growing environment (Jeroch and Abbreviations: AA, amino acid; BW, body weight; DM, dry matter; AME, apparent metabolizable energy; FDBD, feed per bird per day; FDGN, feed-to-gain ratio; ND, nitrogen retained; NSP, non-starch polysaccharide

2 60 CANADIAN JOURNAL OF ANIMAL SCIENCE Dänicke 1995). Broiler diets containing a high level of a cereal with a high level of NSP cause sticky droppings, wet litter, and reduced weight gain (Choct and Annison 1990; Smits and Annison 1996). The negative effects of NSP have prevented the widespread use of rye in poultry diets. They are less serious in barley and wheat and have been reduced greatly by the addition of enzymes that partially digest the β-glucans in barley and the arabinoxylans in wheat (Bedford 1996). Bioassays have been used extensively to measure AME (Askbrant 1990). Scott et al. (1998a,b) described a broilerchick bioassay for cereals that measures AME and ND from excreta samples of chicks at 8 and 16 d of age and from ileal digesta at 17 d. The authors presented values obtained from control samples of wheat and barley that were included in a series of assays of wheat and barley samples over a period of 2 yr. This repetition allowed an investigation of the random variation associated with the bioassay in order to validate the assay. The assays measured AME and ND of 108 samples of wheat and 83 samples of barley grown in western Canada, both with and without supplementation by commercial feed enzymes, which were included to reduce the antinutritive effects of NSP. Bioassays are time consuming, expensive, and subject to bird-to-bird variation. Attempts have been made to predict AME from chemical measures (Sibbald et al. 1963), in vitro digestion (Clunies et al. 1984; Valdes and Leeson 1992a) and near infrared reflectance (Valdes and Leeson 1992b; Swift et al. 1998). These have not been widely applied, although near infrared reflectance of whole-grain samples (Swift et al. 1998) appears promising. Any technique should include measurement of factors that might affect palatability or voluntary intake, which could in turn affect performance. A rapid, inexpensive method of feed evaluation is needed to permit routine screening of cereal grains for ration formulation and to replace the use of values contained in general tables (NRC 1994). These values have been criticised by the feed industry (M. L. Swift, unpublished data) as being inaccurate for Western Canadian grains when fed to broiler chickens. Scott et al. (1998b) investigated the relationship between the AME and ND. This paper aims to relate AME values obtained in the bioassay to performance characteristics of the chicks to better determine the feeding value of the cereal, and to discuss the limitations of bioassay measurements to measure feeding value of a grain. MATERIAL AND METHODS The broiler-chick bioassay for AME (Scott et al. 1998a) uses diets containing 80% of the test cereal, balanced with a basal diet containing concentrated sources of AA, vitamins, minerals, and an acid-insoluble ash marker. The complete diets are fed ad libitum to broiler chicks from 4 to 17 d of age. On reception of the cereal, 1000-kernel weight (g) and bushel weight (kg hl 1 ) are determined. These parameters are used routinely by the feed industry to measure the quality of cereal grains. After mixing, each diet is split: one portion is fed as-is, the other portion is supplemented with 0.15% of an enzyme appropriate for the test cereal (Avizyme TX for wheat and Avizyme SX for barley. Finnfeeds International, Marlborough, Wiltshire, UK SN8 1XN). Duplicate samples of nine wheat cultivars, grown in six environments (three locations in each of two crop years), provided a total of 108 wheat samples. Scott et al. (1998c) reported data on both crop years. However, changes were made in the basal diet between 1994 and 1995, resulting in a significant improvement in broiler performance (growth, feed intake and feed conversion) but no difference in AME (Scott et al. 1998a). This publication therefore reports data from only 1995 (54 samples). Each of these 54 wheat samples was fed in diets with or without a supplemental enzyme source. We also had available a total of 87 barley samples, representing different cultivars and growing environments (differing in crop year and growing location). Each sample was tested with and without enzyme supplementation. Scott et al. (1998c) provided a detailed description of the wheat samples and of 71 of the barley samples. The other 16 barley samples were included in these bioassays but were not replicated in different growing environments and were not included in the statistical analyses described by Scott et al. (1998c), which investigated both genotype and environment effects. The management of the chicks during the bioassay has been described by Scott et al. (1998a), followed guidelines described by the Canadian Council on Animal Care (1993) and has been approved by the Pacific Agri-Food Research Centre Animal Care Committee. Four bioassays were required to measure the 54 wheat samples in 1995, and five bioassays were used to measure the barley samples. The data used for this paper include the levels of AME (DM basis), determined from excreta collected for 24 h at 8 and 16 d of age (AME8, AME16), and ND, determined from ileal digesta collected at 17 d of age. Calculations to determine AME and ND were described by Scott et al. (1998a). Apparent metabolizable energy was not corrected for nitrogen, and true ME was not determined. Data were also obtained on excreta DM at 8 and 16 d (DM8, DM16) and on the viscosity of intestinal contents of chicks fed wheat at 17 d, these being indicators of the NSP content of the grain tested. Performance of the chicks was measured as BW at 17 d; the FDGN from 4 to 17 d of age, and FDBD while on the test diets. Analyses of variance were performed using the General Linear Models procedure of SAS (Littell et al. 1991). The ANOVA for both the wheat and the barley data sets measured the fixed effect of enzyme supplementation. All of the differences were significant and justified further statistical treatment of the data according to enzyme supplementation. Product moment correlation coefficients were calculated between AME and ND measures, viscosity, and excreta DM, and the performance variables BW, FDGN, and FDBD for the wheat and barley assays. The AME intake was determined by multiplying the AME values by the FDBD and correlation coefficients were calculated between AME intake based on AME values at 8 and 16 d and the BW and the FDGN. All correlations were calculated separately for diets with and without enzyme supplementation.

3 SCOTT ET AL. FEEDING VALUE MEASUREMENTS AND BIRD PERFORMANCE 61 Table 1. Broiler performance, feeding value, and physical measurements of 54 wheat samples fed with or without enzyme and the response to enzyme supplementation (X ± SE) z Variable y With enzyme Without enzyme Enzyme response x 17 d BW (g) 448 ± ± ± 0.58 FDBD (g bird 1 d 1 ) 39.3 ± ± ± 0.59 FDGN (g g 1 ) 1.40 ± ± ± 0.38 AME8 (kcal kg 1 diet) 3500 ± ± ± 0.59 AME16 (kcal kg 1 diet) 3650 ± ± ± 0.35 ND (%) 89.8 ± ± ± 0.21 Viscosity (centipoise) 4.3 ± ± ± DM8 (%) 61.7 ± ± ± 0.80 DM16 (%) 60.5 ± ± ± 0.87 Kernel wt. (g 1000 seeds 1 ) 39.9 ± ± 0.88 Bushel wt. (kg hl 1 ) w 76.4 ± ± 0.39 z All differences between the samples with and without enzyme were significant. x [(Value with enzyme value without enzyme)/value with enzyme] 100. w lb bushel = kg hl 1. Table 2. Broiler performance, feeding value and physical measurements of 87 barley samples fed with or without enzyme and the response to enzyme supplementation (X ± SE) z Variable y With enzyme Without enzyme Enzyme response x 17 d BW (g) 459 ± ± ± 0.89 FDBD (g bird 1 d 1 ) 40.2 ± ± ± 0.73 FDGN (g g 1 ) 1.39 ± ± ± 0.90 AME8 (kcal kg 1 diet) 3340 ± ± ± 0.56 AME16 (kcal kg 1 diet) 3370 ± ± ± 0.50 ND (%) 84.0 ± ± ± 0.70 DM8 (%) 53.9 ± ± ± 0.93 DM16 (%) 40.2 ± ± ± 0.69 Kernel wt. (g 1000 seeds 1 ) 39.9 ± ± 0.88 Bushel wt. (kg hl 1 ) w 70.6 ± ± 0.82 z All differences between the samples with and without enzyme were significant. x [(Value with enzyme value without enzyme)/value with enzyme] 100. w lb bushel = kg hl 1. RESULTS The average values for the variables measured for chicks fed wheat samples are presented in Table 1. Chicks fed wheat with enzyme gained more, ate more, and had better feed efficiency than those fed wheat without enzyme. The AME was greater at 16 than at 8 d of age and was greater when diets were supplemented with enzyme. Values for ND obtained from measuring N in the ileal contents were high and significantly improved by enzyme supplementation. Digesta viscosity was decreased greatly by enzyme addition, and excreta DM was increased. The kernel weight and bushel weight were the same for samples with and without enzyme because these were measured on the whole-grain samples at delivery. The average values for chicks fed barley samples are shown in Table 2. Barley and wheat samples were not tested in the same bioassays and could not be compared statistically. However, the performance of chicks fed barley supplemented with enzyme was as good as or better than that of chicks fed wheat, even with lower values for AME content and ND. The digesta viscosity of chicks fed barley was measured initially, but the values were very high, and measurement was discontinued. Excreta DM of chicks fed barley was lower than that of chicks fed wheat. The average kernel weight was the same for barley as it was for wheat, but the bushel weight was lower. Enzyme addition produced a much greater response in performance, feeding value, and excreta DM in barley than it did in wheat, likely reflecting the higher levels of NSP. Correlation coefficients between physical characteristics of the grain (kernel weight, bushel weight), feeding value of the grain (AME and ND), and measures reflecting the NSP level (excreta DM, digesta viscosity) for the wheat samples are shown in Table 3. Correlations between kernel and bushel weights and BW and feed intake were reduced by enzyme addition. In younger chicks, kernel and bushel weights were correlated with excreta DM to a greater degree than in older chicks. All significant correlations between BW and DM were low. Feed intake was correlated with DM8 but not DM16, and the FDGN was correlated with DM8 but not DM16, and only when enzymes were fed. Digesta viscosity was not correlated with BW or feed intake of chicks fed diets supplemented with enzyme, but BW was significantly associated with viscosity when chicks were not fed enzyme. The FDGN was associated with digesta viscosity, and to a greater degree (r = 0.76) without enzyme supplementation than with enzyme. With enzyme supplementation, AME and

4 62 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 3. Correlation coefficients between performance parameters of broilers fed wheat based diets (BW, FDBD, FDGN) and AME, ND, digesta viscosity, excreta DM, and physical measurements of the cereal z With enzyme Without enzyme Variable y BW FDBD FDGN DM8 DM16 BW FDBD FDGN DM8 DM kernel weight NS Bushel weight NS NS NS DM NS NS 0.47 NS NS DM NS 0.27 NS 0.28 NS 0.27 NS Viscosity NS NS 0.49 NS NS 0.76 NS 0.27 AME8 NS NS NS 0.52 NS 0.63 NS 0.39 AME16 NS NS NS 0.37 NS 0.48 NS ND NS NS NS NS NS NS 0.34 NS DM8 Response NS NS NS NS NS 0.42 NS 0.36 DM16 Response 0.33 NS NS NS 0.52 NS 0.68 Viscosity Response NS NS NS NS 0.59 NS NS AME8 Response NS NS NS 0.38 NS 0.33 NS 0.34 AME16 Response NS NS NS 0.44 NS 0.28 NS ND Response NS NS NS NS NS NS NS NS NS 0.23 z There were 54 samples, each fed with and without enzyme; correlations are calculated separately for data sets with and without enzyme addition. Correlation coefficients are different from 0 at P < 0.05 unless indicated by NS (not significant). ND were not associated with BW or feed intake (with the exception of AME8 and feed intake). Without enzyme supplementation, BW, but not feed intake, was correlated with AME value. The association between the FDGN and AME was significant with or without enzyme at 8 d, but only without enzyme at 16 d. There was no significant association between ND and the FDGN. Correlations between the response to enzyme supplementation of wheat samples are also shown in Table 3. Enzyme supplementation reduced the association between BW and DM16, viscosity, and AME measures. The response in feed intake had little association with the change in feed-quality variables (only the correlation with AME8 with enzyme was significant). The relationship between the FDGN and these variables was not significant when diets were supplemented with enzyme but, with the exception of ND, was significant when diets were not supplemented. Correlation coefficients between physical characteristics of the grain (kernel weight, bushel weight), feeding value of the grain (AME and ND), and measures indicating the NSP level (excreta DM, digesta viscosity) for the barley samples are shown in Table 4. The kernel weight was associated only with the FDGN. Bushel weight was associated with excreta DM when diets were supplemented with enzyme and with BW, feed intake, and the FDGN when they were not. Excreta DM was associated with BW in unsupplemented but not supplemented diets. Feed intake was associated negatively with DM at 8 d with enzyme supplementation and positively with DM8 and DM16 without supplementation. Enzyme supplementation reduced the statistical association between DM and the FDGN dramatically. Most of the correlations between performance and AME and ND measures were significant. However, only without enzyme supplementation were they very high, ranging between 0.39 and Enzyme supplementation drastically reduced the statistical association between performance variables and DM, AME, and ND. Relating performance to AME intake, rather than AME itself, resulted in higher correlation coefficients with BW both with and without enzyme supplementation (Table 5). Enzyme supplementation reduced their magnitude, reflecting a reduction in variability. The relationship between AME intake and the FDGN was moderate for barley without enzyme, low to moderate for wheat without enzyme, and was not significant when enzyme was added (the only significant value was low and not in the expected direction). DISCUSSION Data sets containing 54 samples of wheat and 87 samples of barley provided large data sets with variation in both feeding value and performance measures sufficient to test the predictive value of feed-quality measures for chick performance. The grain industry uses physical characteristics of the cereal, such as kernel and bushel weight, to determine its value. The relationship between kernel weight and performance was substantial only for wheat and only when it was fed without enzyme. Even then, the associations were no better than moderate. These data do not support a system of classification based on kernel or bushel weight for barley or wheat fed with enzyme. Lower correlations between kernel weight and performance when enzyme is used may be due to the NSP being contained primarily in the endosperm walls (Jeroch and Dänicke 1995) and the fact that a difference in kernel size will lead to a difference in the proportion of endosperm wall. Digesta viscosity and excreta DM are measures of the antinutritive effects of NSP that are present in varied amounts in wheat and barley and are responsible for reduced chick performance (Bedford 1996; Bedford and Morgan

5 SCOTT ET AL. FEEDING VALUE MEASUREMENTS AND BIRD PERFORMANCE 63 Table 4. Correlation coefficients between performance parameters of broilers fed barley based diets (BW, FDBD, FDGN) and AME, ND, excreta DM, and physical measurements of the cereal z With enzyme Without enzyme Variable y BW FDBD FDGN DM8 DM16 BW FDBD FDGN DM8 DM kernel weight NS NS 0.45 NS NS NS NS 0.32 NS NS Bushel Weight NS NS NS NS NS DM8 NS 0.25 NS DM16 NS NS AME NS 0.31 NS NS AME NS ND NS DM8 Response NS NS 0.33 NS DM16 Response NS NS NS NS NS 0.52 NS NS AME8 Response NS NS AME16 Response NS NS ND Response NS NS z There were 87 samples, each fed with and without enzyme; correlations are calculated seperately for data sets with and without enzyme addition. Correlation coefficients are different from 0 at P < 0.05 unless indicated by NS. 1996). The addition of feed enzymes to reduce the effects of NSP also reduced the predictive value of these measures, especially in barley, because the variation common to predictor and performance variables was reduced. Higher correlation coefficients between excreta DM and performance among barley samples were higher than for wheat samples, especially without enzymes, and reflecting greater variation in the antinutritive effects of NSP in barley. Among barley samples, some correlation coefficients were significant even with enzyme supplementation, suggesting that the use of an enzyme did not completely eliminate the negative effects of NSP. Feed formulation uses the ME levels of feed ingredients because energy is one of the basic nutrients needed for growth. The importance of energy was confirmed by positive correlation coefficients between AME in the cereals and BW and by the negative correlation coefficients between AME and the FDGN. However, while significant, the correlation coefficients were not high enough to allow accurate predictions of broiler performance from the AME values. Addition of enzymes reduced the negative effects of NSP on both AME and performance. Leeson et al. (1996) found that modern broilers retain some ability to control feed intake based on the energy content of the feed. This would suggest that there should be an association between AME and feed intake. However, correlations between feed intake and AME were low or not significant, suggesting that the control of energy intake may in fact be poor when ingredients other than corn or soybean meal are used in diets. Among barley samples without enzyme supplementation, correlation coefficients between AME and feed intake were much higher. They were also positive, in direct contrast to what would be expected if broilers reduced intake to control AME. It seems likely that other factors (such as an antinutritive substance) reduced both AME and feed intake. Table 5. Correlation coefficients between performance (BW, FDGN) and AME intake (AME FDBD) of broilers fed diets based on wheat and barley z With enzyme Without enzyme Variable y BW FDGN BW FDGN Wheat samples (n = 54) AME8 intake 0.67 NS AME16 intake Barley samples (n = 87) AME8 intake 0.75 NS AME16 intake 0.72 NS z Correlations are different from 0 at P < 0.05 unless indicated by NS. y AME8 and AME16, apparent metabolizable energy determined at 8 and 16 d. Supplementation with enzymes to remove the effects of NSP also removed the association, suggesting that these may be an underlying factor. The statistical associations between BW and AME intake were higher than those between BW and AME itself, clearly because energy is a major feed component used for growth. AME intake combines the voluntary intake of the grain and the nutrient content, and the increase in predictive value over AME suggests that cereal palatability may be an underrated factor in determining the performance of growing chicks. In other words, knowledge of the energy content of an ingredient is of little economic value if the ingredient results in low voluntary feed intake. Correlation coefficients between ND and performance, especially in wheat samples, were also low and were similar to those reported by Achinewhu and Hewitt (1979). Statistical associations between ND and performance likely reflected variation in broiler growth, rather than variation in feeding value of the grain. Any system of routine evaluation of cereals for feed formulation must include the energy that a bird will obtain

6 64 CANADIAN JOURNAL OF ANIMAL SCIENCE from the cereal. The AME values obtained from this assay were not adequate for predicting broiler performance, although including a measure of voluntary feed intake increased the accuracy of evaluation. The need for enzyme supplementation of wheat and barley could be determined by measuring the level of NSP. Measuring digesta viscosity itself is labour intensive and routine evaluation would require replacement by an in vitro test such as those suggested by Rotter et al. (1989), Bedford and Classen (1993) and Pack and Bedford (1998). Investigation of the chemical differences between wheat and barley samples that produce similar growth but have different AME levels is the subject of further investigation. ACKNOWLEDGMENTS We would like to gratefully acknowledge the financial support of the Alberta Barley Commission, Canadian Wheat Board, Finnfeeds, Int., IRAP/NSERC, BC Broiler Chicken Marketing Board, and Agriculture and Agri-Food Canada. We would also like to thank Drs J. Helm, B. Rossnagel & P. Hucl for growing and shipping the wheat and barley samples. The poultry staff of PARC (Agassiz) is also thanked for their dedication and hard work in maintaining the birds, collecting and analysing samples. Achinewhu, S. C. and Hewitt, D Assessment of nutritional quality of proteins: the use of ileal digestibilities of amino acids as measures of their availabilities. Brit. J. Nutr. 41: Askbrant, S The concept of metabolizable energy for poultry. Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden. Report 194. Bedford, M. R The effect of enzymes on digestion. J. Appl. Poult. Res. 5: Bedford, M. R. and Morgan, A. J The use of enzymes in poultry diets. World s Poult. Sci. J. 52: Bedford, M. R. and Classen, H. L An in vitro assay for prediction of broiler intestinal viscosity and growth when fed ryebased diets in the presence of exogenous enzymes. Poult. Sci. 72: Canadian Council on Animal Care, Guide to the care and use of experimental animals. 2nd ed., Volume 1. CCAC, Ottawa, ON. Choct, M. and Annison, G Anti-nutritive activity of wheat pentosans in poultry diets. Br. Poult. Sci. 31: Classen, H. L. and Stevens, J. P Nutrition and growth. Pages in P. Hunton, ed. Poultry production. Elsevier Science B.V., Amsterdam, The Netherlands. Clunies, M., Leeson, S. and Summers, J. D In vitro estimation of apparent metabolizable energy. Poult. Sci. 63: Jeroch, H. and Dänicke, S Barley in poultry feeding: a review. World s Poult. Sci. J. 51: Leeson, S., Caston, L. and Summers, J. D Broiler response to diet energy. Poult. Sci. 75: Littell, R. C., Freund, R. J. and Spector, P. C SAS System for Linear Models, 3rd ed., SAS Series in Statistical Applications. SAS Institute Inc., Cary, NC. National Research Council, Nutrient requirements of poultry. 9th ed. National Academy Press, Washington, DC. Pack, M. and Bedford, M. R Best-cost approach optimises enzyme addition. Feed Tech 2: Rotter, B. A., Marquardt, R. R., Guenter, W., Biliaderis, C. and Newman, C. W In vitro viscosity measurements of barley extracts as predictors of growth responses in chicks fed barley-based diets supplemented with a fungal enzyme preparation. Can. J. Anim. Sci. 69: Scott, T. A., Silversides, F. G., Classen, H. L., Swift, M. L., Bedford, M. R. and Hall, J. W. 1998a. A broiler chick bioassay for measuring the feeding value of wheat and barley in complete diets. Poult. Sci. 77: Scott, T. A., Silversides, F. G., Classen, H. L., Swift, M. L. and Bedford, M. R. 1998b. Comparison of sample source (excreta or ileal digesta) and age of broiler chick on measurement of apparent digestible energy of wheat and barley. Poult. Sci. 77: Scott, T. A., Silversides, F. G., Classen, H. L., Swift, M. L. and Bedford, M. R. 1998c. Effect of cultivar and environment on the feeding value of western Canadian wheat and barley samples with and without enzyme supplementation. Can. J. Anim. Sci. 78: Sibbald, I. R., Czarnocki, J., Slinger, S. J. and Ashton, G. C The prediction of the metabolizable energy content of poultry feedingstuff from a knowledge of their chemical composition. Poult. Sci. 42: Smits, C. H. and Annison, G Non-starch polysaccharides in broiler nutrition - towards a physiologically valid approach to their determination. World s Poult. Sci. J. 52: Swift, M. L., Scott, T. A., Classen, H. L. and Bedford, M Prediction of the AME content of whole wheat and barley by NIRS. Proceedings of the Annual Meeting of the Canadian Society of Animal Science, Vancouver, BC. p Valdes, E. V. and Leeson, S. 1992a. Measurement of metabolizable energy in poultry feeds by an in vitro system. Poult. Sci. 71: Valdes, E. V. and Leeson, S. 1992b. Near infrared reflectance analysis as a method to measure metabolizable energy in complete poultry feeds. Poult. Sci. 71: