Energy evaluation of eight barley cultivars for poultry: effect of dietary enzyme addition

Energy Evaluation of Eight Barley Cultivars for Poultry: Effect of Dietary Enzyme Addition1 M. J. VILLAMIDE,*,2 J. M. FUENTE,† P. PEREZ DE AYALA,† and A. FLORES† *Departamento de Produccio´n Animal, E.T.S.I. Agro´nomos, Universidad Polite´cnica, 28040 Madrid, Spain, and †Trouw Ibe´rica S.A. Ronda de Poniente 9, 28760 Tres Cantos, Madrid, Spain DM; 3,192 vs 2,929 kcal TMEn/kg DM). Two-rowed cultivars showed higher TMEn than six-rowed winter cultivars, although no differences were found for AMEn. The correlation between AMEn and TMEn values of barley was relatively low (r = 0.69); therefore, barley TMEn cannot be extrapolated to AMEn for young chicks. Enzyme addition produced an average increase of 220 kcal/kg DM in barley AMEn (P < 0.001); there was a significant (P < 0.10) interaction between barley cultivar and enzyme supplementation. The increment of barley AMEn caused by enzyme addition was partly explained (47%) by an increase in barley viscosity. This relationship implies that enzyme supplementation significantly improves the feeding value of high as compared to low viscosity barley samples, which involved a decrease in AME n variation among cultivars for enzymesupplemented barley. No relationship was found between AMEn of unsupplemented barley cultivars and their chemical composition. Instead, a relationship was detected for enzyme-supplemented barley; therefore two equations were proposed for predicting the AMEn of enzyme-supplemented barley to be used directly in diet formulation.

(Key words: nitrogen-corrected apparent metabolizable energy, nitrogen-corrected true metabolizable energy, barley, enzyme, poultry) 1997 Poultry Science 76:834–840

value, with and without enzyme addition, is essential to establish an accurate quality:price ratio for feed formulation. The fastest and cheapest way to obtain energy value determinations is the TMEn method (Sibbald, 1986); however, extrapolation of this energy value to feeding of chicks is questionable. Extensive work has been done to study the effect of enzyme addition to poultry diets on the energy value of barley (Rotter et al., 1990; Friesen et al., 1992; Fuente et al., 1995). A significant increase due to enzyme addition was found for AMEn values; however, no differences were found for TMEn values determined with adult roosters (Rotter et al., 1990, Fuente, 1995). Rotter et al. (1990) explained this lack of effect based on the age of the animals. Likewise, Almirall et al. (1993) reported no differences in digestive enzyme activity (trypsin, amylase, and lipase activity) or ileal digestibility when high

INTRODUCTION Barley is the cereal most extensively used for animal feeding in Spain (51% of total cereals) because of its adaptation to dry climates and hardiness. However, its use for poultry, mainly chicks, has been traditionally restricted due to its low energy value and associated problems such as sticky droppings (Gohl et al., 1978). The use of dietary enzymes to improve the utilization of barley in poultry is a common practice when wheat or corn prices are high. A good estimation of barley energy

Received for publication June 16, 1996. Accepted for publication January 8, 1997. 1Financial support provided by Centro para el Desarrollo Tecnolo´gico e Industrial. Project Number 910050. 2To whom correspondence should be addressed.

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ABSTRACT Three experiments were conducted to study eight barley cultivars and the effect of enzyme addition on their energy value for poultry. In Experiment 1, the AMEn of a reference barley (Beka cultivar) was calculated by increasing barley concentrations (30, 40, 50, and 60%) that replaced a high protein basal diet. In Experiment 2, eight barley cultivars (four spring and four winter cultivars) replaced the reference barley in the diet with 50% barley inclusion. Two of the winter cultivars were two-rowed and two were six-rowed cultivars. A commercial enzyme was added to these diets to study the effect of enzyme addition. Diets were consumed ad libitum by 27 and 145 21-d-old Arbor Acres broiler chicks, in Experiments 1 and 2, respectively. In Experiment 3, 66 adult roosters were used to determine the TMEn of the eight cultivars used in Experiment 2. Dietary AMEn decreased linearly (P < 0.05) with increasing barley (Beka cultivar) inclusion. Beka barley AMEn was calculated by extrapolation of the linear regression equation be equal to 2,980 kcal/kg DM. Barley energy value was influenced by cultivar (P < 0.001); the spring cultivars showed greater energy value than the winter cultivars (2,963 vs 2,852 kcal AMEn/kg

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BARLEY ENERGY VALUE AND ENZYME ADDITION TABLE 1. Composition of experimental diets, Experiment 1 Barley concentration Ingredients and analysis

30%

40%

50%

60%

(%) 30.0 41.2 15.8 1.4 7.1 0.8 0.2 1.6 0.9 0.2 0.8

40.0 34.9 13.4 1.2 6.0 0.8 0.2 1.6 0.9 0.2 0.8

50.0 28.6 10.9 1.0 5.0 0.8 0.2 1.6 0.9 0.2 0.8

60.0 22.3 8.5 0.8 3.9 0.8 0.2 1.6 0.9 0.2 0.8

2,994 27.9 1.7 1.0 1.0 0.4

2,959 25.4 1.5 1.0 1.0 0.4

2,924 22.8 1.3 0.9 0.9 0.4

2,890 20.4 1.1 0.8 0.9 0.4

1Supplied per kilogram of diet: selenium, 0.1 mg; iodine, 2 mg; cobalt, 0.2 mg; copper, 4 mg; iron, 29 mg; zinc, 38 mg; manganese, 65 mg; sulfur, 120 mg; retinyl acetate, 7,500 IU; cholecalciferol, 1,500 IU; dl-a-tocopherol acetate, 7.5 IU; riboflavin, 3 mg; pantothenic acid, 6.5 mg; menadione sodium bisulfite, 1.5 mg; vitamin B12, 10 mg; niacin, 15 mg; choline, 250 mg.

barley diets were supplemented with enzymes and fed to cockerels, although a reduction in the intestinal viscosity was observed. They concluded that the intestinal viscosity was not a limiting factor in Leghorn cockerels as it is in young birds (Almirall et al., 1993). Time without feed and amount of feed intubated in the TMEn methodology may change transit time and, possibly, the viscosity of the gut digesta, which could alter the effects of enzyme addition. Therefore, the effect of enzyme addition was not evaluated in adult roosters when TMEn was measured in the present research. On the other hand, direct determinations of the energy value of feedstuffs require lengthy and expensive metabolism experiments, so there has been considerable interest in the prediction of energy value of feedstuffs, such as barley, by establishing relationships with chemical analyses that are easily performed in a laboratory. The objectives of this work were: 1) to determine the energy value (AMEn and TMEn) of eight barley cultivars, 2) to study the effect of dietary enzyme addition on the AMEn of these cultivars, and 3) to predict barley energy value from its physico-chemical characteristics.

MATERIALS AND METHODS Three experiments, the two first performed simultaneously, were carried out to achieve these objectives. In Experiment 1, the AMEn of a barley cultivar (Beka), used as a control, was determined by a multi-level assay. In Experiment 2, eight cultivars of barley and the effect of enzyme addition on their AMEn were evaluated in relation to the AMEn of the barley used as a control. In Experiment 3, the TMEn of the barley cultivars,

previously tested in Experiment 2, was determined directly.

Experiment 1: AMEn of Beka Barley Cultivar Four diets with increasing concentrations (30, 40, 50, and 60%) of barley (Beka cultivar) replacing a high protein basal diet (Table 1) were supplied to 27 21-d-old Arbor Acres broiler chicks (6 to 7 per diet). Diets were formulated to meet or exceed the National Research Council (1984) requirements for 50% barley inclusion to minimize dietary imbalance in the extreme diets. After a 7-d adaptation period to the experimental diets, chicks were deprived of feed for 16 h, then allowed ad libitum access to the diets during 4 d, and deprived of feed again for 16 h prior to the end of the collection period. Total excreta voided during the balance period (4 d) were collected twice (at 48 and 96 h), and frozen at –20 C. Excreta samples were dried in a forced air draft oven at 70 C for 48 h, and then ground for determination of gross energy and nitrogen. Correction to zero nitrogen retention was made using 8.22 kcal/g of retained nitrogen (Hill and Anderson, 1958). The AMEn of the Beka barley cultivar was calculated by extrapolation to 100% of inclusion of the linear regression equation between dietary AMEn and barley level.

Experiment 2: AMEn of Barley Cultivars With and Without Enzyme Addition Eight Spanish barley cultivars grown in 1993 (including the one used in Experiment 1) were used in this experiment. Four of these samples were grown in the

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Barley grain Soybean meal Full-fat soybean Sunflower seed meal Pork lard Methionine (20%) Lysine (20%) CaHPO4 CaCO3 NaCl Vitamin mineral premix1 Calculated analyses ME, kcal/kg Crude protein Lysine Methionine + cystine Calcium Available phosphorus

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VILLAMIDE ET AL. TABLE 2. Chemical composition (on a DM basis) of barley cultivars, Experiment 2 and 3 Spring cultivars

Winter cultivars

Two-rowed cultivars

Two-rowed cultivars

Six-rowed cultivars

Beka

Gabriela

Klaxon

Clerix

Alpha

Joline

Dobla

Hatif de Grignon

Dry matter, % Ash, % Crude protein, % Crude fiber, % Ether extract, % Sugars, % Starch, % Gross energy, kcal/kg Total NSP, % Arabinose, % Galactose, % Glucose, % Mannose, % Rhamnose, % Xilose, % Total b-glucans, % Viscosity, cst b-glucanase activity, U/g

89.1 2.6 14.1 3.9 1.9 2.5 60.8 4,420 12.37 2.44 0.24 4.77 0.32 0.05 4.52 3.62 4.93 < 6

89.2 2.7 11.3 4.1 1.5 2.2 63.1 4,384 11.97 2.14 0.20 5.23 0.26 0.07 4.07 3.30 4.83 < 6

88.7 2.3 12.3 4.5 1.5 2.0 62.2 4,382 10.20 1.87 0.17 4.28 0.20 0.05 3.63 3.45 6.75 < 6

87.9 2.5 16.5 3.9 1.6 3.1 54.7 4,302 16.51 1.95 0.20 10.71 0.27 0.06 3.32 3.60 4.32 < 6

88.4 2.0 14.8 4.9 1.5 1.4 56.2 4,423 13.02 2.32 0.25 5.41 0.24 0.06 4.74 3.93 5.77 < 6

88.5 2.1 12.2 4.5 1.8 1.5 57.4 4,371 11.79 1.93 0.18 5.51 0.18 0.05 3.91 4.40 7.03 < 6

87.8 2.2 11.5 4.3 1.6 1.5 59.1 4,350 15.64 1.98 0.21 9.73 0.19 0.06 3.47 3.90 3.60 17

89.0 2.9 11.2 7.6 1.6 1.3 55.3 4,384 19.90 2.23 0.24 11.75 0.25 0.06 5.37 4.20 4.82 11

spring (spring cultivars) and the other four in autumn (winter cultivars). All the spring varieties were two-row cultivars. Among the winter varieties, there were two two-row and two six-row cultivars. Chemical composition, nonstarch polysaccharides (NSP) characterization, viscosity, and b-glucanase activity of all cultivars are shown in Table 2. The different barley cultivars replaced the control barley in the diet with 50% barley inclusion used in Experiment 1. This barley inclusion level was chosen because the highest response to enzyme addition was observed at this rate in previous work (Fuente et al., 1995), and because it is a practical rate in commercial diets for young chicks. Eight additional diets were obtained by adding a multi-enzyme complex containing 100 U/g of bglucanase (EC 3.2.1.6), 300 U/g xylanase (EC 3.2.1.8), and 800 U/g protease (EC 3.4.24.28) activity from Trichoderma and Aspergillus species3 to study its effect on AMEn. The 16 diets were fed to 118 21-d-old Arbor Acres broiler chicks (6 to 8 per diet), following the methodology described in Experiment 1 to determine dietary AMEn. Fecal DM content was determined during the balance period (4 d) of the metabolism assay. The energy value of barley samples was calculated by reference to the AMEn of the Beka cultivar, according to the following equation: AMEn Barley = AMEn Beka +

(AMEnBD – AMEn BekaD) 0.5

where AMEn BD = AMEn of diets with the different barley cultivars and AMEn BekaD = AMEn of the diet that includes the Beka cultivar at 50%. 3Avizyme

1100, Finnfeeds International Ltd., Marlborough, UK.

In both experiments, diets were supplied in mash form after milling using a screen size of 2.5 mm, and were assigned to chicks at random. Chicks were housed in individual metabolism cages of 0.19 m wide, 0.39 m long, and 0.31 m high, with raised wire floor, individual feeders and cup drinkers providing free access to feed and water.

Experiment 3: TMEn of Barley Cultivars The precision-fed cockerel assay of Sibbald (1986) was used for determining the TMEn of the eight barley cultivars used in Experiment 2. The birds were housed in individual metabolism cages, 0.31 m wide, 0.40 m long, and 0.49 m high. Following a period of 24 h without feed, 30 g of the different ground barley samples were fed by intubation to 55 (6 to 8 per treatment) adult cockerels (HyLine, 1-yr-old). At the same time, another eight cockerels were deprived of feed to estimate the endogenous energy losses. Total excreta voided over the following 48-h period were dried and ground for subsequent analyses, as described for Experiment 1. Roosters were assigned to treatments at random. The three experiments were conducted at the Experimental Farm of Trouw Ibe´rica S.A. The animals were held in environmentally controlled rooms with a temperature ranging from 23 to 27 C. The lighting program during assays for both chicks and roosters was 16 h:8 h light:dark. Throughout the experiments, the animals were handled according to the principles for the care of animals in experimentation established by the Royal Decree 223/88 of Spain (1988).

Analyses Dry matter, ash, CP, crude fiber (CF), ether extract, sugars, and starch were analyzed according to AOAC (1984) methods. The NSP content of barley was deter-

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Composition

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BARLEY ENERGY VALUE AND ENZYME ADDITION TABLE 3. Effect of barley inclusion on dietary AMEn, Experiment 1 Barley inclusion

AMEn

(%) 30 40 50 60 SEM Linear effect of barley inclusion

(kcal/kg DM) 3,098.1 3,068.8 3,027.8 2,998.1 66.3 0.005

Linear regression equation Barley AMEn, kcal/kg DM calculated by extrapolation

Probability

AMEn = 3,320.8 – 3.41 %Barley r2 = 0.98 RSD = 23.54 2,979.8 ± 64.571

√

as V (reg) 1/n + (1 – BI¯)2 / [S BI2i – (S BIi)2/n] where V (reg) is the variance of the regression in the number of data, and BIi are numerical values of barley inclusion. 1Calculated

RESULTS Dietary AMEn decreased linearly (P < 0.01) with barley inclusion (Table 3, Experiment 1), about 34 kcal for each increase of 10% units of barley. Beka barley AMEn was calculated by extrapolation of the linear regression equation to a 100% of barley inclusion. The mean value obtained for this cultivar was 2,980 kcal AMEn/kg DM. Chemical composition of barley samples studied in Experiments 2 and 3 presented a high variability (CV of 22%) in the structural component of cell walls (CF and NSP content) and barley viscosity. However, the variation of b-glucan content was very low (ranging from 3.3

4Waters

Model 150, Waters (Division of Millipore), Milford, MA

01757. 5Kapillar Viskosimeter Number 516-10, Schott-Gerate GmbH, D 6238 Hofheim a. Ts., Germany. 6IKA-4000, Shotch Ibe ´ rica, Spain.

to 4.4%), showing slightly higher values (P = 0.0046) for winter than for spring cultivars (4.1 vs 3.5%, respectively). The effect of barley cultivar and enzyme addition on dietary and barley AMEn is shown in Table 4. Barley cultivar had a significant effect (P < 0.001) on dietary AMEn. Calculated AMEn values of barley cultivar ranged from 2,802.8 to 3,049.6 kcal/kg DM for Hatif de Grignon and Beka cultivars, respectively. Spring cultivars had higher (P < 0.01) energy values than winter cultivars (AMEn of 2,963.3 vs 2,851.6 kcal/kg DM); however, no differences were found when comparing two- vs six-rowed winter cultivars. Enzyme addition increased (P < 0.001) dietary AMEn (110 kcal/kg on average, Table 4). An interaction (P = 0.08) between barley cultivar and enzyme addition was detected, as can be observed by the different responses to enzyme addition in barley AMEn (improvements from 4 to 15.7%). Fecal DM content (data not shown) differed (P < 0.01) among diets with different barley cultivars (from 26 to 35% for Klaxon and Clerix cultivars, respectively) and improved (28 vs 31.5% DM) with dietary enzyme addition (P < 0.001). A barley cultivar by enzyme interaction was also detected (P < 0.10), due to the different responses to enzyme addition of the barley cultivars (the increase in DM content was 1 and 45% for Gabriela and Joline cultivars, respectively). Barley TMEn was affected by the growing season and the number of rows of barley cultivars (Table 5, Experiment 3). Similarly to AMEn, spring cultivars had higher TMEn than winter cultivars (3,191.9 vs 2,928.8 kcal/kg DM) but, in this case, differences were found between two- and six-rowed winter cultivars (3,018.1 vs 2,839.6 kcal/kg DM, respectively).

DISCUSSION The AMEn of Beka barley (2,980 kcal/kg DM, Table 3), used as a reference, was estimated with high precision (2.1% CV) due to the high barley levels used

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mined by gas liquid chromatography4 (English and Cummings, 1984) and barley viscosity using an Ostwald viscometer5 (Henry, 1984). Endogenous b-glucanase activity was determined following the McCleary and Schemeer (1987) methodology. Gross energy was measured with an adiabatic bomb calorimeter.6 Statistical analyses were performed for each experiment by using the SAS General Linear Models procedure (GLM) (SAS Institute, 1985). Regression analyses were performed to quantify the dietary AMEn change as a function of barley inclusion. A two-way analysis of variance was carried out by GLM procedure to study the effect of barley cultivar, enzyme addition, and their interaction. Orthogonal contrasts were performed to compare the energy value of spring vs winter barley cultivars and two- vs six-rowed winter cultivars. Stepwise regression analyses was done to determine the chemical components that best predicted the energy value of barley.

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VILLAMIDE ET AL. TABLE 4. Effect of barley cultivar and enzyme addition on dietary and barley AMEn, Experiment 2 Dietary AMEn

Barley AMEn

Barley cultivar

No enzyme

Enzyme

Beka Gabriela Klaxon Clerix Alpha Joline Dobla Hatif de Grignon SEM Source of variation Barley (B)2 Enzyme (E) B × E

3,027.8 2,917.1 2,928.2 2,959.6 2,944.9 2,868.0 2,943.2 2,909.6

(kcal/kg DM) 3,101.2 2,979.8 3,053.1 2,751.2 3,090.7 2,773.3 3,067.4 2,836.1 3,001.9 2,806.7 3,076.9 2,652.9 3,018.6 2,803.3 2,976.3 2,736.1

1Percentage

Enzyme

Enzyme1 improvement

3,119.3 3,023.2 3,098.3 3,051.7 2,920.7 3,070.8 2,954.2 2,869.5

(%) 4.7 9.8 11.7 7.5 4.0 15.7 5.3 4.8

65.9

of barley AMEn improvement due to enzyme addition. contrast: Spring vs winter cultivar (P = 0.0015); two- vs six-rowed winter cultivar (P = 0.85).

and the good linear fit between dietary AMEn and barley levels. This AMEn value was in the range of data obtained with chicks and reported in the literature (from 2,600 to 3,097; Rotter et al., 1990; Viveros et al., 1994; Fuente et al., 1995), but was lower than that predicted by equations available in the literature (3,320 and 3,247 kcal/kg DM according to INRA, 1981, and WPSA, 1986, respectively). The reason of this difference between actual and predicted values could be the age of the animals, because prediction equations were determined from data obtained from adult Leghorn cockerels. Pentosans and b-glucans are the major barley dietary fiber components; the mean values in the cultivars studied were 6.2 and 3.8%, respectively. Despite the lower quantitative importance of the b-glucans, its location in the endosperm of the grain (99 vs 22% of total b-glucan and pentosan contents in the endosperm, respectively; Henry, 1987) makes them the main antinutritional factor in barley grain, acting as a physical impediment to nutrient hydrolysis and utilization by digestive enzymes (Bedford, 1992). The low variation of

TABLE 5. The TMEn of barley cultivars, Experiment 3 Barley cultivar

Barley TMEn

Beka Gabriela Klaxon Clerix Alpha Joline Dobla Hatif de Grignon SEM Orthogonal contrasts Spring vs winter cultivar Two- vs six-rowed winter cultivars

(kcal/kg DM) 3,412.6 3,087.9 3,248.9 3,018.2 3,129.2 2,906.9 2,852.6 2,826.5 116.8 Probabilities 0.0001 0.0003

the b-glucan content among cultivars (Table 2), and its lower than expected content could be related to a greater extent to growing and harvest conditions (such as weather, geographical location, and agronomic practices) than to cultivar (Pe´rez Vendrell et al., 1993). All the varieties studied were grown in central Spain, characterized by dry and hot weather. Francesch et al. (1992b) indicated that the geographical location explained 65 and 46% of b-glucan variation for 1987 and 1988, respectively. By contrast, barley viscosity, also highly related to harvesting conditions (Hesselman and Thomke, 1982; Campbell et al., 1989), presented much higher variation in the samples studied. The effects of cultivar on barley energy value were observed in both broiler chicks (AMEn, Table 4) and adult roosters (TMEn, Table 5). The higher energy value of spring cultivars is explained by their higher starch and lower CF, NSP, and b-glucan content. Similarly, Francesch et al. (1992a) found higher AMEn (100 kcal/ kg) for spring than for winter cultivars, when AMEn was determined on 57 varieties of barley with roosters. However, the higher NSP content of six- vs two-rowed (Table 2) winter cultivars only affected the TMEn value, in the current study. As would be expected, barley TMEn was greater than AMEn (3,060 vs 2,792 kcal/kg DM, respectively), and the correlation between TMEn and AMEn was relatively poor (r = 0.693, P = 0.056). Although the mean value of barley TMEn was similar to the mean value of enzymesupplemented barley AMEn (3,011 kcal/kg DM), their correlation was poorer (r = 0.651, P = 0.081), which indicated that digestive utilization differed between roosters and chicks (Almirall et al., 1993). The TMEn values of the different barley cultivars had a greater range (587 vs 327 kcal) and a greater CV (6.6 vs 3.4%) than AMEn values. This effect was higher when TMEn was compared with AME n values for enzymesupplemented barley. Therefore, it could be inferred that

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2Orthogonal

13.7 Probabilities 0.0009 0.0001 0.0791

No enzyme

BARLEY ENERGY VALUE AND ENZYME ADDITION

Barley AMEn increment (kcal/kg DM) = –109.4 + 63.01 viscosity (cst) r2 = 0.47; P = 0.062. This relationship implied a greater effect of enzyme supplementation on high than on low viscosity barley samples, which involved a decrease in AMEn variation among enzyme-supplemented barley cultivars (their range decreased from 327 to 249 kcal/kg and the CV from 3.37 to 2.97%). A differential effect of enzyme addition on AMEn of barley cultivars was found by Rotter et al. (1990), who obtained the greatest response to enzymes for barley cultivars with the greatest viscosity, although no mathematical relationship was shown. In the same work, the AMEn of unsupplemented barley cultivars was negatively related to soluble bglucan and viscosity. The effect of barley cultivar on fecal DM content was related to barley viscosity (r = –0.78, P < 0.05) in unsupplemented diets; thus, an increase of 1 cst in barley viscosity produced an increase in fecal moisture of two percentage points. Gohl et al. (1978) stated that the cause of sticky droppings when barley was fed to poultry was a result of the viscous nature of the digesta, which was hydrolyzed by b-glucanase. In the current study, the increase in fecal DM content due to enzyme addition was positively related (r = 0.77, P < 0.05) to bglucan content of barley. This relationship could be explained by the effect of b-glucan on increasing gut viscosity (White et al., 1983) and the clear decrease of gut viscosity caused by enzyme addition (Almirall and Esteve-Garcı´a, 1994; Fuente et al., 1995). No significant relations among AMEn values of unsupplemented barley cultivars and their chemical composition were found in the current study. Likewise, Francesch et al. (1992a), working with a larger number of cultivars, pointed out the low correlation of barley AMEn and their chemical parameters. However, both AMEn values of enzyme-supplemented barleys and TMEn values of barley were significantly related to NSP

contents (r = –0.703 and –0.642, respectively). Barley TMEn was negatively related (P < 0.1) to NSP-glucose (r = –0.711), the major component of NSP, and to b-glucan content (r = –0.621). The highest correlation of enzyme-supplemented barley AMEn with chemical composition could be related to the release of nutrients (Bedford, 1992) and the decrease of gut viscosity (McNab and Smithard, 1992) produced by the added enzymes, which would lead to a stronger effect of nutrients, positively or negatively, on barley AMEn. Thus, the following equations were obtained relating chemical parameters and the AMEn of enzymesupplemented barleys (n = 8): AMEn = 3,269.8 – 54.4 CF r2 = 0.545; RSD = 65.2; P = 0.0365 AMEn = 2,784.0 + 203.7 EE + 72.0 Sugars – 17.3 NSP r2 = 0.915; RSD = 34.4; P = 0.0129. Crude fiber variation was responsible for 55% of the AMEn variation of enzyme-supplemented barley; however, this parameter only explained 13% of the AMEn variation of unsupplemented barley. Nonstarch polysaccharides, sugars, and ether extract contributed 49, 31, and 11%, respectively, to the AMEn variation of enzyme-supplemented barley. From these equations, the AMEn of enzymesupplemented barley can be estimated from fast chemical analyses to be used in diet formulation with higher precision than using a mean value from tables. The main practical implications that can be inferred from the current study are: 1) enzyme addition reduces the variability in the AMEn of different barley cultivars because of its greater effect on the worst barley cultivars (higher viscosity); and 2) the AME n of enzymesupplemented barley can be estimated from chemical parameters, mainly CF and NSP.

ACKNOWLEDGMENTS The authors gratefully acknowledge the valuable comments of Javier Piquer and Fernanda Soto-Salanova during the preparation of this paper.

REFERENCES Almirall, M., and E. Esteve-Garcı´a, 1994. Rate of passage of barley diets with chromium oxide: Influence of age and poultry strain and effect of b-glucanase supplementation. Poultry Sci. 73:1433–1440. Almirall, M., J. Brufau, and E. Esteve-Garcı´a, 1993. Effects of intestinal viscosity on digestive activities of intestinal content and ileal digestibilities of poultry fed barley diets at different ages supplemented with b-glucanases. Pages 69–72 in: Proceedings of the 1st Symposium of Enzymes in Animal Nutrition. Kartause Ittingen, Switzerland. Association of Official Analytical Chemists, 1984. Official Methods of Analysis. 14th ed. Washington, DC.

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barley TMEn values must not be extrapolated to (unsupplemented or enzyme-supplemented) barley AMEn values for chicks. The increase in barley AMEn (7.8%) caused by enzyme addition (Table 4) was similar to those reported in the literature. Rotter et al. (1990) reported an average increase in AMEn of 5.4% working with four different cultivars; whereas Francesch et al. (1994), working with three cultivars, reported a 5% increase although one of the cultivars (Beka) increased by 8%; and Fuente et al. (1995) reported an increase of 7% for barley inclusion levels of 50%. These AMEn increases could be explained by a greater nutrient digestibility, as suggested by Salih et al. (1991) and Viveros et al. (1994). The incremental magnitude of barley AMEn with enzyme addition depended on barley viscosity according to the following equation:

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