Effect of Trichoderma viride enzymes in pelleted broiler diets based on barley

Effect of Trichoderma viride enzymes in pelleted broiler diets based on barley

:lmmnl Fred Scrrrm and Technulo~,~~,34 ( I99 I ) 193-202 Elsevicr Science Publishers B.V.. Amsterdam 193 Effect of Trichoderma viride enzymes in pel...

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:lmmnl Fred Scrrrm and Technulo~,~~,34 ( I99 I ) 193-202 Elsevicr Science Publishers B.V.. Amsterdam

193

Effect of Trichoderma viride enzymes in pelleted broiler diets based on barley

ABSTRACT

An expernnent was conducted with I440 chicks 10 determine the effect ofadded Trrclrodum Cride cnrymes (WE) in pelleted broiler diets based on barley (35% from 0 to 19 days, 45% from 19 10 45 days) a, 0. 100 and 200 mg kg-‘. The ,I-&can conlcn, of the barley was 1.8%. Addition oFTVE significantly improved wcighc gain by 2.1% ano feed to gain ratio by 2.39bthrougbcul the experiment. The improvcmcm was grealcr in the finisher period ( 19-45 days) than in the grower period (O-19 days). These results suggest thal TVE cnrymes arc efl’eclw~ even at low fl-glucan concentrations. during Ihe finisher period, and in pelleted drcts.

INTRODUCTION

The utilization of barley in broiler diets is limited because of its low energy content. This and the presence of/?-glucans mean that, even at a competitive price, it is usually limited to about 20% of the diet. The /Sglucans, which are found at concentrations between 2 and 8% depending on variety, season of cultivation, climate, and time of harvesting (Hesselman et al., 1981; Hesselman and Thomke, 1982) are indigestible and cause an increase in the viscosity of the intestinal contents (Burnett, 1966, Edney et al., 1989). This interferes with the digestion and absorption ofnutrients (Ikegami et al., 1990). In addition, barley causes the adherence of faeces to the cloaca of birds (sticky droppings) during the first weeks of life and increases the moisture content of faeces (Gohl et al., 1978). which creates management and health problems (Pattison, 1987). The application of enzymes with /3-glucanase activity improves the nutri‘Author

to whom

03.,‘7-8401/91/$03.50

correspondence

0

should beaddressed.

1991 Elsevier Science Publishers

B.V.

All rights reserved.

194

J BRVFhU ELSL.

tive value of diets containing high barley levels (about 60%) (Broz and Frig, 1986; Hesselman et al., 1982; Hijikuro, 19831, and decreases the viscosity of the intestinal contents (White et al., 1981, 1983) and the incidence of sticky droppings (Elwinger and Saterby, 1987). These beneficial effects have been obtained with mash diets, and in general the experiments have been conducted with chicks up to 3 weeks of age. The thermostability of the enzymes is variable depending on the source (Chesson, 1987). This is critical when these products are used in pelleted

diets, because the temperatures achieved during the pelleting process can cause their inactivation. Campbell et al. (1984) suggested that, given the dietary composition ofbroiler diets and the conditions of pelleting, the thermostability of these products should be assured. Recently, Elwinger and Saterby (1987), Broz (1989) and Wiedmer and VGlker (1989) have conducted experiments with these enzyme preparations in pelleted diets, and have obtained a response to enzyme supplementation in feed conversion using low energy diets with about 60% barley. It can be concluded that in many of the experiments mentioned, the barley concentrations were very high, the energy !evels of the diets low, and in most cases, the diets were not pelleted. Therefan , the objective of the present study was to determine the response to pglucanases from Trichoderma viride (TVE) in pelleted diets at higher energy levels ( 12.5-12.9 MJ kg-’ of ME) and barley inclusions of 35% and 45% in the starter and finisher diets, respectively, which are conditions similar to those found in commercial practice. MATERIALSA;!?* METHODS A total of 1440 sexed l-day-old chicks of the Arbor Acres strain were distributed by sex in 36 pens. Each pen contained 40 males or 40 females. The pens were each 4 m! in size. Chicks were housed in a windowless house provided with forced ventilation, artificial light and gas heaters. The experiment lasted 45 days. Feed and water were supplied ad libitum throughout the experiment. There were three treatments: ( 1) a basal diet with 35% barley in the grower period and 45% barley in the finisher period (Table 1); (2) as Treatment 1 with 100 mg kg-’ of TVE added; (3) as Treatment 1with 200 mg kg-’ TVE added. Two diets were used throughout the experiment: Arstly, a starter diet from 0 to 19 days of age containing 12.5 MJ kg-’ of ME and 21% protein; secondly, a finisher diet from 19 days to the end of the experiment at 45 days of age, containing 12.9 MJ kg- ’ and 19% protein. Diets were prepared with a 2 mm sieve in the hammer mill and steam pelleted using a pelleting machine of 20 HP (Mabrik, S.A., Santa Perpetua de la Mogoda, Barcelona, Spain), with a matrix of 40 cm diameter with holes 40 mm deepx4 mm wide. The steam pressure was 3 atm, and the yield was 1100 kg h-‘. The average tem-

TABLE I Compoailian ofthe basal diets (‘WI

M&e. yellow Ewlcr

Full fact exrrudcd soya beans Calcium carbonale Calcium dtphosphate Sodium chloride L-lysinc HCI rx-melhmninc 8.Ape-carotcnoic ester Canlhaxanthm Mineral and vitanun prcmm Lnaalortd (m% kg-l offccd, Virginamycm (mg kg-’ offeed) Calculated ~~mpowlm” Me~abolirablc energy (MI kg-’

PrLl1cm

Mclhioninc Mclhionincfcyetinz Llsinc Calcium .Available phosphorus Tom, fat

)

Grower

Finisher

22. I 35.0 2.9 4.0 I.5 21.0 9.8 I.0 1.5 0.28 0.08 0.16 0.03 0.001 0.4 90 20

lb.? 45.0 4.0 5.0 1.0 12.Q 12.8 0.8 I.5 0.25 0.016 0.048 0.016 0.004 0.4 90 20

12.5 21.0 0.51 0.87 1.15 0.9 0.38 7.73

i 2.9 19.0 0.38 0.70 0.95 0.8 0.38 10.07

‘Composilion ofthc mineral andvitamin premix (kg-’ feed): vitamin A. I2 OOOIU: D,. 2400 IIJ: E. I5 mg: K. 6 mg: B,. 2 mg: B1. I I mg: pantothenic acid, 24 mg: nicolinic acid. 36 mg: vitamin B,. 4 mg: B,,. 0.02 mg: folic aad. 0.5 mg; Mn, 60 mg; Zn, 40 mg: LO.35 mg; Fe, 80 mg; Cu. 8 mg: Se. 0. I5 mg: clhonyquin. 100 mg.

peratures were measured during the pelleting process at 5-min intervals and are shown in Table 2. The diets were allocated at random to six replicates of

40 male chicks and six replicates of40 female chicks per treatment. Moisture, ash, crude libre, ether extract and crude protein contents were determined for gross chemical composition (Association of Official Analytical Chemists, 1984); viscosity was determined according to the method of De Silva et al. ( 1983). Total /I’-gucans were determined by the enzymatic method of McCleary and Glennie-Holmes ( I985 ), and insoluble &lucans were separated from solublefi-glucans following the procedure ofAman and Graham (1987)

196

J. BRUFhUETAL.

TABLE 2 Averagelcmperatures during the pelleting process Dictsl

TVE’ (mg kg-’

T-l T-2 T-S

)

Pelletmgwmperaturc (CC)’ I

2

3

0 100 200

83 (85)” 73 (78) 76 (77)

68 (70) 63 (64) 64 (66)

64 (66) 62 (64) 63 (64)

0 100 200

65 (66) 65 (67) 68 (70)

58 (59) 55 (56) 58 (60)

60 (64) 56 (60) 58 (58)

Ruirher T-l T-2 T-3 ‘Tr,chodcmu

w,dmzy&.

.

‘1. lemperaturc of mash at the point of steam additixx: 2, lerrmcraturc of mash before matrix: 3. lcmperalure of pcllcts after ma1rix.

‘Average of fivemeasurementstaken at)-min inlervals. and maximum lcmperaturc achieved during the process. TABLE 3 Chemical analysis of the experimental diets f’anmcren

Diet (and mg kg-’ WE)’ T-l (0)

T-2 (100)

T-3 (2001

9.34 5.56 3.25 8.45 20.83 2.19 1.31 0.52

9.19 5.63 3.22 8.43 20.60 2.25 1.32 0.53

8.79 5.66 3.27 8.54 21.05 2.08 1.30 0.51

9.54 5.09 3.67 10.04 IS.47 53.19 2.38 1.37 0.80

9.46 5.08 3.14 IO.01 18.56 53.75 2.35 1.50 0.67

9.41 5.05 3.36 9.55 18.32 54.31 2.53 I .54 0.57

Gmiv.9

MDklU*e Ash Crude fibrc Ether cxtracl Crude protein Viscosily’ Total 8.glucans Insoluble~-glucane F;r!;rhw Moisture Ash Crude tibr. Elhc:extrsct Crude protein N-free-extract Viscosity’ Total /?&cans lnsoleblc/Sglucans

‘Control war a basal barley-maize-soya diet. TVE. Trichodrrrna virideenzymcs. ‘Viscosity (&I) at pH 5.

FFFK

, ot

I

I

,n,,x

ENZYMES

IN SRCNLER

DlETS

197

and were subsequently determined following the method for total p-gluca.ns. Chemical composition of the diets is shown in Table 3. The barley used In this experiment had the following characteristics: 66.62 specific gravity, 10.36% moisture, 2.18% ash, 4.36% crude fibre, 1.76% fat, 8.33% crude protein, 1.6’% &lucans of which 1.49% were insoluble (92% of the total) and 3.55 cSt of viscosity at pH 1.5. Feed and chicks were weighed on Day 19, when chicks were changed to the finisher diet, and at the end of the experiment, on Day 45. Daily weight gain, daily feed consumption and feed to gain ratio were calculated for each period and for the overall experiment. Mortality was recorded daily. Incidence of faeces adhered to the cloaca (sticky droppings) was recorded at 8 and I6 days of age, and expressed as the percentage of animals with sticky droppings in each pen. Treatment means were separated by Duncan’s test (Steel and Torrie, 1980) as no sexxtreatment interactions were found. RESULTS

AND DISCUSSION

Average body weight, daily weight gain, daily feed consumption and feed conversion ratio for the grower period (O-19 days), finisher period (19-45 days) and for the overall experiment (O-45 days) are shown in Table 4. No significant sexx treatment interactions were found for any parameter and period examined. Sex effects were significant (PcO.05) for weight gain and feed consumption in all periods and for feed conversion ratio, only for the finisher period. In the starter period, the addition of200 mg kg-’ TVE significantly improved feed conversion (PcO.05) over the basal diet, while the addition of 100 mg kg-i TVE gave results not significantly different from those for the other treatments. In the finisher period, chicks given TVE at both levels gained more weight than controls. Feed conversion was better for chicks given 100 mg kg-’ TVE than controls, while 200 mg kg-’ TVE gave intermediate results. The overall results showed a significant improvement of weight gain caused by the inclusion of TVE at both levels. Feed conversion ratio was better for the chicks given ‘I’VE at 100 mg kg-’ than the controls, while those given 200 mg kg- ’ were intermediate and not different from either of the other treatments. The incidence of sticky droppings in the chicks is shown in Table 5. Significant differences (P-zO.01) were found at 8 days of age. Chicks fed on the control diet showed a higher incidence than those on the treatments with enzyme supplementation. When chicks were I6 days old, the percentage of sticky droppings decreased. Chicks fed on the control diet still had a higher incidence, but treatment means were not significantly different (P> 0.05). Enzyme supplementation improved the overall daily weight gain and feed conversion of the trial by 2.7% and 2.3%, respectively. This suggests that the temperature achieved during pelleting (Table 2) did not affect the stability

O-19 days T-l T-2 T-3 Sex DictXScx Pooled standard

TVE (wkg-‘)

Body weight w

Weight gain @day-‘)

Feed CO”S”lllptlO” C$day-‘)

0 100 200

527 528 536 I.,

27.8 27.8 28.2 111

36.6 36.2 36.5 1.1

NS 3.6

NS 0.2

NS 0.3

1.319= 1.303’” 1.296” NS NS 0.008

1403Q 1447” 1445”

53.9” 55.6” 55.6”

120.3 120.7 121.4

2.253O 2.185b 2.213=’

.I.

111

..I

. .

NS

NS

NS

error

IY-4Sdaw T-l T-2 T-3

0 100 200

sex DiclXScx Pooled standard O-45 don T-l T-2 T-3 SCX Diet X%X Pooled standard

_

13.5

error 0 100 200

0.6

1.1

NS 0.012

l930b 1975” 1982’ *..

42.9b 43.9’ 44.1”

84.3 84.7 85.0 I..

1.989 1.943b 1.956’”

NS

NS 0.3

NS 0.7

:: 0.015

error

12.0

‘Means of I2 replicalcs of 40 chicks per treatment. Means with different superscripts in the same column are significanrly 10 Duncan’s test.

diffcrem

(PC 0.05

)according

TABLE 5 Incidence

(%) ofsticky

Diet T-l

T-2 T-3

droppings

(males+females) TVEtmeke-‘) 0

100 200

8 davs

lb davs

14.58’ 8.54b 9.17b

Il.25 6.46 8.54

Pooled sLmdard errm

I .42

‘Means ofsix replicates of 40 chicks each ser. Means with different superscripts in the same column are significantly IO Dunca?‘s test.

dil%cnt

1.60

(P-=0.05

)according

of the enzyme. This could be attributed, at least in part, to the composition of the diet, which contained more than 4% added fat that could reduce friction in the pelleting matrix. This is also supported by the lack of a linear response to TVE level, suggesting that maximum response was obtained with 100 mg kg-’ TVE. If the doses of enzymes were not in excess and if the enzymes had lost some of their activity during pelleting, one would expect more response at the higher TVE level. The response was greater in the finisher period ( 19-45 days) with a daily weight gain and feed conversion ratio 3.1% and 2.9% better than the control diet, than in the period O-19 days, where feed efficiency was improved only by 1.2%and 1.7% with 100 and 200 mg kg-’ of TVE, respectively. Although there were no significant sexxtreatment interactions, the improvements obtained were numerically superior in males than females (4.6% vs. 1.4% in daily weight gain and 4.6% vs. 2.1% in feed conversion ratio) which suggests some relationship with the higher growth and feed consumption of males. The effect of enzyme supplementation in mash diets is an improvement of around 7 to around 10% in feed conversion (Hesselman, 1989), while in pelleted diets the effect is less (2.5-4.59/n) as shown in the present and other experiments (Elwinger and Saterby, 1987; Wiedmerand Viilker, lU89). It is interesting to note that the improvement in feed conversion is higher than could be expected from theB-glucan content of the diet (barley was included at 45% in the finisher diet and its&glucan content was 1.61%), if al! the improvement in feed conversion was attributed to the digestion of/?-gJucan.This suaaests that the imorovement of the nutritive value of the diet caused bv enzyme supplementation is due to better digestion of other nutrients of the diet, and is in agreement with the observations of White et al. (1983) and Edney et al. ( 1989). One possible explanation for the bwereffects ofenzyme supplementation observed in pelleted diets could be the improvement of the availability of energy caused by the pelleting process (Farrell et al., 1983; Broz, 1989). Consequently, enzyme supplementation would have less opportunity to cause an improvement, as its mode of action might be similar to that of pelleting. Pelleting results in a large number of ruptured cell walls (Elwinger and Saterby, 1987), especially in barley particles, and enzymes may act by making nutrients more accessible to digestive enzymes. In pelleted diets, the enzyme preparation would be able to improve the nutritive value of ingrcdients already of high energy value, although to a lesser extent. Still, this improvement in pelleted diets may represent substantial economical benefits, as the maninal cost of enerav increases with the enerav level of the diet. The results of this experiment indicate that rhcaddition of /I-glucanases improves the nutritive value of barley during the finisher period. This is in agreement with the reports of Elwinger and Saterby (1987), Wiedmer and Volker ( 1989) and Rotter et al. (1989a). Thus, for example, the latter investigators found that the addition of enzymes for 6 weeks was better than addi-

200

J. BRVFA” ETAL.

tion for the lirst 2 or 4 weeks of age only. These results suggest that the benefits of enzyme addition are manifested even until the age of slaughter, which is longer than indicated by Saterby ( 1985), Pettersson et al. ( 1987), PetterssonandAman (1988) andclassenet al. (1988). Petterssonand Aman (1988) indicate that, in other cereals, there is a lack of response in the finisher period because birds adapt to the presence of pentosans. However, the results presented herein may be influenced by the properties of the barley (especially /Iglucan content, viscosity and length and conditions of storage). In this experiment, storage lasted more than 10 months, and was done under Mediterranean conditions. This reduces the dormancy of the barley, which may be caused by a reduction of the /J-glucan concentration (Molina-Cano et al., 1989) as the low &lucan content of the barley used ( 1.8%) suggests. Possibly for this reason, the control diet did not produce a high incidence of sticky droppings (Table 5) although it was still significantly higher than for the diets with enzyme supplementation at 8 days of age. This could also be the reason why the efficiency of the enzyme compounds was not as high during the first weeks of age as is normally found. The results of the experiment did not show differences between inclusion levels (100 and 200 mg kg-‘), possibly because of the characteristics of the barley used, which agrees with the results of Wiedmer and Vijlker ( 1989) and Rotter et al. (1989b). This seems to indicate that 100 mg kg-’ of enzyme addition was already enough for the barley used, which had a low fi-glucan content, most of which was insoluble ( 1.49% out of a total of 1.61%). This also suggests that a small quantity of soluble&lucans is enough to reduce the nutritive value of basley, as shown by the improvements observed during the finisher period, or that p-glucanases can also degrade insolublep-glucan. The results of this experiment indicate that supplementation of pelleted broiler diets based on barley with Trichoderma viride enzymes significantly improves the performance of broiler chicks up to the age of slaughter. This improvement may be achieved with barleys of low P-glucan content at levels of inclusion of 35% and 4S%, and ME levels of 12.5 MJ kg-’ and 12.9 MJ kg-’ in the starter and finisher diets, respectively. ACKNOWLEDGEMENT

The authors wish to express their gratitude to Hoffman La Roche Ltd. for funds and materials in support of this project.

REFERENCES Aman, P. and Graham. H., 1987. Analysis of total and insoluble mixed-linked beta-o&cans in barley and oats. J. Agric. Food Chem., 35: 704-705.

(l-3).

(l-4)-

Association of Official Analytical Chemists, 1984. Official Methods of Analysis, 14th edn. A.O.A.C.,Washingto.t. DC, pp. 152-169. Broz. J., 1989. Evaluation of Trichodcnna virideenzyme complex as a feed additive for broilers. In: Proceedings of the 7th European Symposium on Poultry Nutrition, Lloret de Mar, Spain, June 1989. IRTA, Barcelona, pp. 303-304. Broz, I. and Frigg, M., 1986. Effects of cellulolylic enzyme products on the feeding value of vartous diets. Arch. Gefliigelkd., 50: 104-l IO. Burnett. G.S., 1966. Studies of viscosity as the probable factor involved in the improvement of certain barleys for chicks by enzyme supplementation. Br. Poult. Sci., 7: 55-75. Campbell, G.L., Classen, H.L. and Salmon. R.E., 1984. Enzymesupplcmcntation ofharley diets for broilers. Feedstuffs. 56( 19): 26-27. Chcsson. A.. 1987. Supplementary enzymes to improve the utilization of pig and poultry diets. In: Recent Advances in Animal Nutrition. Butterworths. London, PD. 71-89. Classen, H.L., Campbell, G.L. and Grootwassink, J.W.D.. 1988. In&wed feeding value of Saskatchewan-grown barley for broiler chtckens with dietary enzyme supplementation. Can. 1. Anim. Sci., 68: 1253-1259. De Silva. S.. Hesselman. K. and &nan, P., 1983. Effects ofwater and fl-glucanase treatment on non-starch polysaccharides in endosperm of low and high viscous barley. Swed. J. Agric. Res.. 13:211-219. Edney. M.J., Campbell, G.L. and Classen, H.L., 1989. The effccl offiglucanase supplememation on nutrient digestibility and growth in broilers given diets containing barley, oat groats or wheat. Anim. Feed Sci. Technol., 25: 193-200. Elwinger, K. and Saterby, B., 1987. The use of~glucanase in practical broiler dietscontaining barley or oats. Swed. J. Agric. Res., 17: 133-140. Farrell. D.J., Thomson. E,. and Choice, A., 1983. Effects of millingand pelleting of maize, barley and wheat on their metabolizable energy velue for cocker& and chicks. Anim. Feed Sci. Technol.. 9: 99-105. Gohl. B., Alden, S.. Elwinger. K. and Thomke, S., 1978. Influence ofj&canase on feeding value of barley for POUI~IY and moisture content of encreia. Br. Pot&. Sci.. 4 l-47. Hesselman. K., (989. The “be of enzymes in poultry diets. In: Proceedings oiths 7th European Symposium on Poultry Nutrition, Lloret de Mar. Spain. June 1989. IRTA, Barcelona, pp. 31-48. Hesselman, K. and Thomke, S., 1982. Influence of some factors on development of viscosity in the water ofharley. Swed. J. Agric. Res., IZ: 17-22. Hesselman, K., Elwinger, K., Nilsson, M. andTh<~mke, S., 1981. The efl’ectof~-glucanase supplementation, stage of ripeness, and storage treatment of barley in diets fed to broilerchickens. Pouli. Sci., 60: 2664-2671. Hcsaclman. K.. Elwinger, K. and Tbomke, S., 1982. Influence ofincreasinglevelsof&ghtcanase on the productive vi.lue of barley diets for broiler chickens. Anim. Feed Sci. Tcchnol., 7: 351-358. Hiiikuro. S.. 1983. Impmvement of fcedtna value of barlev~. bv enzvme suoolementation. Jon. ~ . -Agric. Res. Q., 17( 55-58. Ikegami, S.. Tsuchihashi, F., Harada. H., Tsuchihashi, N.. Nishide, E. and Innami, S., 1990. Effect of viscous indigestible polysaccharides on pancreatic-biliary secretion and digestive organs in rats. J. Nutr., 120: 353-360. McClew. B.V. and Glenn&Holmes. M.. 1985. Enzvmic auantification of (l-31. (1-4)-/?-p glucan in barley and malt. J. Insl. Brew., 91: 285-i95. Malina-Cano, J.L., Rota de Togores, F., Royo. C. and Perez. A., 1989. Fast germinating lowa glucan mutants induced in barlcy with improved malting quality and yield. Theor. Appl. Genet., 78: 748-754.

broiler

19:

extract

i 1:

.,

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Pattison, M., 1987. Problemsofdiarrhoea and wet litter in meal poultry. In: Rcccnt Advances in .Animal Nulrilion, Bullerworlhs. London. pp. 27-37. Pcttcrsson, D. and Aman, P., ,988. Effects ofenzyme supplementation of diets based on wheat. rye or lriwale on their productive value for broiler chickens. Anim. Feed Sci. Technol.. 20: 313-324. Peltersson, D.. Graham, H. and Aman, P., 1987. The productive value of whole and dehullcd oats in broiler chicken diets, and influence ofp-glucanase supplementation. Nuir. Rep. Im.. 36: 743-750. Rotter. B.A., Neskar. M.. Guenler, W. and Marquardt, R.R.. 1989a. Effect of enzyme supplementalion on the nutritive value of hulless barlcy in chicken duels. Antm. Feed Sci. Tcchnol., 24: 233-245. Roltcr, B.A., Neskar. M., Marquardt, R.R. andGuenter. W., 1989b. Effcclsofdiffcrcnt enzyme oreoarationsan the nutritional valueofbarlev in chicken diets. Nulr. Rev. Int.. 39: 107-120. S&dv. B.. 1985. Enzymetfl-alucansand aackt&hlineodret undcrolika l&tid au uppodningcn: Rep. Poult. Div., Dep. Anim. Nutri. M&ge..Uppsala, Sweden. 1980. Principles and Procedures of Slaiislics: A Biometrical Steel, R.G.D. and Torrie, J.H.. Approach, Zndedn. McGraw-Hill. New York. White. W.B., Bird. H.R.. Sunde, M.L., Prentice. N., Burger, W. and Marlctt, J.A.. 1981. The viscosity interaction of barley j%&can with Trrchodcnna Wide cellulase m the chick inlcstine. Poult. Sci., 60: 1043-1048. White, W.B.. Bird, H.R.. Sundc. M.L.. Marlett, J.A., Prentice, N.A. and Burger, W.C., 1983. Viscosity ofl%walucan as a factor in Lheenzymatic improvement of barley for chicks. Poult. Sci., 62:853-861. Wwdmer. H. and Viilker. L., 1989. Enzyme supplementation of barley bared diet fed lo broiler chickens under practical conditions. In: Proceedings of the 7th European Symposium on Poultry Nutrition, Lloret de Mar. Spain, June 1989. IRTA, Barcelona. pp. 322-323.