Revista Científica ISSN: Universidad del Zulia Venezuela

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1 Revist Científic ISSN: Universidd del Zuli Venezuel Urdnet-Rincón, Mrí; Leeson, Steven EVALUATION OF VARIED DIETARY CRUDE PROTEIN AND LYSINE LEVEL AT 5.7 OF CRUDE PROTEIN ON PRODUCTIVE PARAMETERS IN BROILER CHICKENS. Revist Científic, vol. XVIII, núm. 2, mrzo-ril, 2008, pp Universidd del Zuli Mrcio, Venezuel Disponile en: Cómo citr el rtículo Número completo Más informción del rtículo Págin de l revist en redlyc.org Sistem de Informción Científic Red de Revists Científics de Améric Ltin, el Crie, Espñ y Portugl Proyecto cdémico sin fines de lucro, desrrolldo jo l inicitiv de cceso ierto

2 Revist Científic, FCV-LUZ / Vol. XVIII, Nº 2, , 2008 EVALUATION OF VARIED DIETARY CRUDE PROTEIN AND LYSINE LEVEL AT 5.7 OF CRUDE PROTEIN ON PRODUCTIVE PARAMETERS IN BROILER CHICKENS. Evlución de diferentes niveles de proteín crud y lisin l 5,7 de proteín crud sore prámetros productivos de pollos de engorde. Mrí Urdnet-Rincón nd Steven Leeson Fcultd de Ciencis Veterinris, Universidd del Zuli, Mrcio-Venezuel. Animl nd Poultry Science Deprtment, University of Guelph, Ontrio, Cnd. E-mil: urdnetm@yhoo.com ABSTRACT An experiment ws crried out to evlute the performnce of 1-18 d roiler chickens to dietry crude protein (CP) levels from 170 to 250 g CP/kg diet nd the dietry lysine level formulted t 5.7 of CP level. Thus, the dietry lysine level of diets incresed s CP incresed. Body weight gin of chicks ws ffected t ges from 1 to 18 dys y the CP nd lysine levels. Birds fed the most protein diets t ges from 0 to 7 nd 7 to 14 dys were heviest (P<0.05) for dietry CP of 25 vs 19 nd 17. Incresed ody weight gin (0-18 d) (P<0.05) ws found with incresing dietry CP from 210 to 250 g CP/kg diet compred to lower CP levels. Dietry tretments hd no effect on dily feed intke (g//d) when CP levels were 190 to 250 g CP/kg diet (P>0.05). There ws reduced feed intke with dietry CP t 170 g CP/kg diet (P<0.05). As dietry crude protein incresed there ws n increse of out 31 in crcss nitrogen deposition (mg//d) when chicks were fed diets from 210 to 250 g CP/kg diet compred to the lower CP diets (P<0.05). A decrese in crcss ft deposition (g//d) ws found s dietry CP incresed from 170 to 250 g CP/kg diet. This study indictes tht if lysine to CP rtio is kept constnt t 5.7, mximl productive performnce of roiler chickens to 18 dys cn e chieved mong 21 nd 25 CP. Choosing mong diets will depend minly on cost of the dietry protein. Key words: Broilers, crude protein, lysine level, weight gin, crcss nitrogen. Reciido: 15 / 11 / Aceptdo: 18 / 05 / RESUMEN Un experimento fue relizdo con el fin de evlur l respuest productiv y deposición de N y grs en pollos de engorde desde el 1 los 18 dís de edd limentdos con niveles de proteín crud (PC) vrindo desde los 170 los 250 g PC/kg diet y el nivel de lisin formuldo l 5,7 del nivel de PC de l diet. L gnnci de peso fue fectd en tods ls eddes por los niveles de PC y lisin. Ls ves limentds con diets conteniendo 210; 230 y 250 g CP/kg, desde el 1 los 14 dís de edd, presentron myor peso (P<0,05). Un umento en l gnnci de peso (0-18 d) (P<0,05) se encontró l incrementr los niveles de PC de g PC/kg y comprrlos con menores niveles de PC. El consumo dirio de limento (g//d) no fue fectdo cundo los niveles de PC fueron de g PC/kg (P>0,05). Se encontró un disminución en el consumo de limento con diets conteniendo 170 g PC/kg (P<0,05). Se oservó un tendenci de mejorr l conversión limentici (C: A) l suministrr lts concentrciones de PC en l diet. Ls ves limentds con g PC/kg otuvieron un incremento de proximdmente un 31 en l deposición de nitrógeno en l cnl (mg//d) comprdos con ls ves limentds con menores niveles de PC (P< 0,05). L deposición de grs (g//d) en l cnl de ls ves disminuyó l umentr l proteín en l diet desde los g PC/kg. Este estudio sugiere que, cundo el rdio de lisin: PC es mntenido 5,7, un desrrollo productivo máximo en pollos de engorde los 18 dís de edd puede ser lcnzdo con diets entre de PC. L escogenci del nivel de proteín dependerá principlmente del costo de l diet. Plrs clve: Pollos de engorde, proteín crud, nivel de lisin, gnnci de peso, deposición de nitrógeno en l cnl. 154

3 Revist Científic, FCV-LUZ / Vol. XVIII, Nº 2, , 2008 INTRODUCTION Dietry protein content hs re-emerged s topic of interest nd importnce over the lst few yers minly due to environmentl concerns. An incresing understnding of protein utiliztion hs llowed to meet more closely the mino cid requirements of roiler chickens t vrious stges of growth. The primry function of protein is to supply essentil mino cids (EAA). Lysine is usully the second limiting mino cid in commercil roiler diets nd other EAA re lnced with this in pplying the concept of idel protein. Lysine is used s the reference AA minly due to its importnce for protein ccretion nd mintennce, the fct tht its determintion is reltive esy, nd numerous dt hve een collected for poultry [7, 18]. The dvntge of the concept of idel AA pttern is tht requirements of other EEA cn e esily estlished under vrious conditions (environmentl, sex, dietry fctors) if lysine requirements re ccurtely known. Reserch hs een conducted to determine the lysine requirements of roiler chickens [8, 16, 20, 21, 22]. However, the need for EAA my vry with the crude protein (CP) level of the diet [27, 28]. In developing countries nd/or when the price of soyen mel increses, need for lterntive ingredients occur which might imply formulting diets higher in CP thn is usully deemed necessry in order to meet norml levels of mino cids. It hs een suggested tht the mount of lysine needed to mximize growth rte when dietry CP vries from 140 to 280 g CP/kg diet is out 54 g lysine/kg CP [1, 27], which implies liner reltionship etween this mino cid nd protein content of diet. The ojective of the present experiment ws to evlute in 1-18 d roiler chickens, the effect of fixing the lysine: protein rtio in the diet t crude protein levels rnging from 170 to 250 g CP/kg diet. MATERIALS AND METHODS Experiments Two hundred nd forty one dy-old mle roiler chickens of commercil strin (Ross x Ross) were rndomly llocted to one of five tretments of 48 chicks ech. Ech tretment consisted of six replictes of 8 irds ech. The experiment ws repeted in time, thus totl of 96 irds were used for ech tretment. Chicks were housed in n electriclly heted ttery rooder where feed nd wter were ville d liitum. Lighting ws provided 23h/dy. All irds were fed d liitum to 18 d of ge with one of 5 experimentl diets. Experimentl diets were individully formulted nd provided 170, 190, 210, 230 or 250 g CP/kg diet while the lysine level ws fixed t 5.7 CP. Other mino cids were formulted ccording to the idel rtio s suggested y Bker nd Hn [7]. At dy 7, ll irds were wing-nded nd individully weighed, nd then reweighed t weekly intervls nd t 18 d of ge. Cge men feed intke nd feed efficiency were lso clculted, nd ll mortlities were recorded. At the strt of the experiments (dy 1) 8 representtive irds, sed on verge ody weight, were killed nd the entire crcsses pooled nd frozen for susequent nlyses. At 18 d of ge, rndom smples of 4 irds per cge were euthnized y cervicl disloction nd the complete crcsses pooled nd then frozen for estimtes of nitrogen nd ft deposition. Crcss yield for ech tretment group ws ssessed s the men of 48 chickens. In ll cses irds were deprived of food for out four hours efore eing killed nd crcss nlyses were determined for the entire ody including fethers. Broiler crcsses were utoclved (Amsco Egle Grvity, Egle Series, 2021) U.S.A., t 120 C for 35 minutes, cooled nd then ground in commercil lender (Wring Products Division, New Hrtford, CT ). Crcss nitrogen determintion ws ssessed using Leco nitrogen nlyzer (Leco Instruments, Stockport, Cheshire, SK7 5DA, UK). Anlyses for ether extrct were ssessed ccording the Assocition of Officil Anlyticl Chemists procedures [5]. Sttisticl Anlysis Not significnt differences were found when ANOVA procedure ws used for vrition in time period, thus the experiment ws rrnged s complete rndomized lock design with replicte s the experimentl unit. A one-wy ANOVA ws used to test the effect of dietry tretments. Response vriles hving significnt F test (P<0.05) were nlyzed using Tukey s studentized rnge test [32]. RESULTS AND DISCUSSION The clculted proximte nlysis nd the determined crude protein (CP) nd lysine levels of the experimentl diets re shown in TABLE I. Dietry lysine level of diets incresed s CP incresed in the diet so s to mintin the lysine: CP rtio t round 5.7 CP. However, there ws lower concentrtion thn estimted for lysine in the diet contining 230 g CP/kg diet (TABLE I). The results of the production prmeters in reltion to vried dietry crude protein nd lysine levels re shown in TABLES II nd III. Body weight gin ws ffected (P< 0.05) t ll ges y dietry CP nd lysine levels (TABLE II). As erly s 7 d of ge, dietry protein with lysine t 5.7 CP influenced weight gin (TABLE II). No significnt differences (P> 0.05) were noted in weight gin of chicks fed mong 25, 23 nd 21 CP. Birds fed the most protein were heviest, nd this ws significnt (P<0.05) for 25 vs 19 nd 17 CP. When evluting the effect of diet protein from 0-18 d of ge, n incresed ody weight gin ws found with incresing dietry CP from 210 to 250 g CP/kg diet compred to diets t 170 nd 190 g CP/kg (P<0.05) (TABLE II). It ws ovious tht vrition in the prmeters mesured depended on the crude protein nd lysine intkes. Previous reserch using low CP diets suggested tht the supply of mino N s non-essentil mino cids (NEAA) ffects growth nd feed conversion [9, 23, 155

4 Vried Dietry Crude Protein nd Lysine Level t 5.7 of Crude Protein on Productive Prmeters / Urdnet-R., M. nd Leeson, S. TABLE I EXPERIMENTAL DIETS COMPOSITION/ COMPOSICION DE DIETAS EXPERIMENTALES Ingredients Crude Protein () Soy en (48) Corn Corn Strch Animl Veg-Ft Limestone Diclcium Phosphte Slt Vitmin-Minerl Premix L-Lysine HCL DL-Methionine L-Threonine Cellulose Clculted Anlysis ME (kcl/kg) Lysine () Methione + Cystine () Threonine () Tryptophn () Sodium () Clcium () Av. Phosphorus () Ft () Fier () Determined Anlysis () Crude Protein Lysine Supplied per kilogrm of diet: vitmin A, 8,800 IU (retinyl plmitte); vitmin D 3, 3,300 IU; vitmin E, 40 IU (dl-=-tocopheryl cette); rioflvin, 8.0 mg; iotin, 0.22 mg; thimin, 4 mg; pntothenic cid, 15.0 mg; vitmin B 12, 12 µg; nicin, 50 mg; choline, 600 mg; vitmin K, 3.3 mg; folic cid, 1.0 mg; ethoxyquin, 120 mg; mngnese, 70 mg s mngnous oxide 60; zinc, 70 mg s zinc oxide 72; copper, 10 mg s copper sulphte 25; iron, 60 mg s ferrous sulphte 30; iodine, 1 mg, nd selenium, 0.3 mg. 2 Contined 23 C nd 20 P. 26]. Current results suggest tht even when essentil mino cids re not limiting in low CP diets need for N in form of NEAA is necessry to optimize growth. This fct is in ccord with the findings of [11] indicting tht even when meeting or exceeding [30] recommendtions of EAA in low CP diets, roiler performnce gols re not chieved compred to irds fed more norml levels of CP diet. However, Aletor et l [2] oserved no difference in growth of roilers fed with dietry CP rnging from 153 to 225 g CP/Kg diet while meeting the minimum [30] recommendtions for EAA. It is likely tht ny excess of EAA would e trnsminted for NEAA synthesis in low CP diets lthough, excess of EAA re used rther efficiently for NEAA iosynthesis [3]. These sme uthors suggested tht the efficiency of lysine used for synthesis of glutmte is only out 45, which implies n extr energetic cost for NEAA iosynthesis tht could id in the explntion of the reduced growth in chicks fed low CP diets. Trnsmintion of EAA increses the synthesis of NEAA nd promotes of uric cid. The cost of energy for uric cid synthesis hs een estimted of 18 ATP per mole [12]. It is suggested tht the reduced response oserved in chicks sujected to low CP diets with lysine t out 5.7 CP is due to n insufficiency of mino N. Bker [ 6] suggested tht the efficiency of utiliztion of protein or n mino cid is constnt from zero up to the miniml requirement for mximl protein ccretion. The reduced weight gin oserved in chicks fed dietry CP of 25 with lysine fixed t 156

5 Revist Científic, FCV-LUZ / Vol. XVIII, Nº 2, , 2008 TABLE II WEIGHT GAIN OF BROILER CHICKENS FED LYSINE FIXED AT 5.7 OF CRUDE PROTEIN LEVELS / GANANCIA DE PESO EN POLLOS DE ENGORDE ALIMENTADOS CON LISINA FIJADA AL 5,7 DEL NIVEL DE LA PROTEINA CRUDA Crude Protein Lysine Weight Gin (g) 0 7d 7 14d 0 14d 0 18d g//d c c c SEM c Mens within column with no common superscript differ significntly (P<0.05). SEM: stndrd error of men. TABLE III FEED CONVERSION AND FEED INTAKE OF BROILERS CHICKENS FED LYSINE FIXED AT 5.7 OF CRUDE PROTEIN LEVELS/ CONVERSION ALIMENTICIA Y CONSUMO DE ALIMENTO EN POLLOS DE ENGORDE ALIMENTADOS CON LISINA FIJADA AL 5,7 DEL NIVEL DE LA ROTEINA CRUDA Crude Protein Lysine Feed Conversion (F:G) Feed Intke 0-7 d 7 14 d 0 14 d 0 to 18 d g//d c c d SEM c Mens within column with no common superscript differ significntly (P<.05). SEM: stndrd error of men. 5.7 CP might e explined s n incresed oxidtion of the mino cid necessitting n extr energy cost, nd therefore less net energy would e ville for production. Mcleod [25] suggested tht 6 mol ATP/mol mino cid is the cost of excretion of N from AA. When supplying mino cid in excess of the immedite need for protein synthesis their oxidtion increses [13], nd so the supplied of mino cids re more efficiently used for protein synthesis when supplied t moderte or requirement levels. Nieto et l. [29], evluted the effect of protein qulity on energy requirements nd energy cost for protein nd ft deposition nd indicted utiliztion of ME for production to e negtively correlted with protein qulity of diets. The sme uthors found tht the energy retined s ft increses s protein qulity declines. A qulity of protein is referred s the profile of the EAA in the proper order to meet the requirements of prticulr species [24]. It is implicit tht even though high CP diets llow for mximl growth, this will not occur with n imlnced mixture of AA s. Diet hd no effect on dily feed intke (g//d) with dietry CP rnging from 190 to 250 g CP/kg diet (P>0.05) nd only with dietry CP diets t 170 g CP/kg there ws reduced feed intke (P<0.05). A noticele improvement in feed conversion (F:G) from the first week of ge ws found when higher concentrtions of CP were fed (P<0.05). Feed conversion from 0-18 d ws not different (P>0.05) for the different diet protein nd lysine levels lthough, differences were noted (P<0.05) when compring 250 vs 170 g CP/kg diets. Ft, crohydrte nd protein ll exert n effect on food consumption lthough, it is suggested tht protein produces the gretest effect in the control of food intke [10]. Results oserved in the experiment suggest tht feed intke ws influenced y dietry crude protein nd lysine levels. Previous reserch conducted with roiler chickens indicte tht feed intke is ffected y dietry CP nd mino cid levels [2, 31] nd tht, in humns t lest, the proportion of circulting mino cids re relted to series of events tht ffect ppetite [10]. D Mello nd Lewis [15] reported tht when chicks were fed n imlnced diet the plsm mino cid profile ws ltered. The fct tht irds my hve n ility to control protein nd/or mino cid intke [14] nd tht they et to fulfill their EAA requirements [33] suggest tht feed intke my e relted to the crude protein nd lysine intkes. However no significnt differences (P>0.05) were oserved in feed intke in chicks fed dietry CP rnging from 190 to 250 g CP/kg diet. A significnt (P< 0.05) reduction in feed intke ws oserved with the lowest CP diets (17). Emmert et l [19] suggested reltionship etween feed intke nd CP, 157

6 Vried Dietry Crude Protein nd Lysine Level t 5.7 of Crude Protein on Productive Prmeters / Urdnet-R., M. nd Leeson, S. especilly t low levels of CP, sitution seen in the current studies. It hs een previously suggested tht when chicks re fed diets deficient in mino cids [4] nd/or excesses of mino cids, feed intke is reduced [15]. However, with the low CP diets used here, dietry lysine levels determined were t or ove 1 of the diet, suggesting tht it ws not lysine, ut rther protein per se, which ffected feed intke. Crcss nitrogen nd ft deposition in chicks to 18 d of ge re presented in FIGS. 1 nd 2. Crcss nitrogen deposition (mg//d) incresed s dietry CP incresed, which resulted in n incresed crcss nitrogen deposition of out 31 in diets rnging from 210 to 250 g CP/kg diet compred to 170 nd 190 g CP/kg diet (P<0.05). There ws lso decrese in crcss ft deposition (g//d) s dietry CP ws incresed. Crcss nitrogen nd ft deposition were relted to CP of diet. An improved (P<0.05) crcss protein ccretion ws oserved when chicks were fed 210 to 250 g CP/Kg diet. Similr responses using diets vrying in CP hve een reported [2, 11, 19]. Eits et l [17] indicted tht protein deposition increses s mino cid intke increses. This correltes with the results of the present experiment where lysine ws fixed t 5.7 CP, wherein s lysine nd CP intkes were incresed crcss nitrogen deposition ws improved. A reduced AA intke of round 6 ws noted in the two lowest CP tretments which hd different (P<0.05) crcss protein deposition compred to the 210 to 250 g CP/Kg diet. This significnt difference however, ws most likely relted to reduction of out 40 in the CP intke etween oth dietry tretments. Ft deposition tended to decrese s dietry CP ws incresed suggesting tht fter the miniml protein/aa requirements re chieved ny excess is degrded nd used for ft synthesis following its demintion. However, the energy required to ctolize the excess of protein nd/or AA my explin the sitution y which incresing dietry CP level ft deposition is reduced. These results re in greement with [2] nd [11], who oserved n increse in ft deposition (g/chick) s dietry CP ws reduced. Ng (m g//d)(0-18d) CP () SEM = Lysine () FIGURE I. NITROGEN GAIN IN BROILER CHICKENS FED LYSINE FIXED AT 5.7 OF CRUDE POTEIN/ GANANCIA DE NITRÓGENO EN POLLOS DE ENGORDE ALIMENTADOS CON LISINA AL 5,7 DEL NIVEL DE LA PROTEÍNA CRUDA Fg (g//d) CONCLUSIONS CP () SEM= The results otined in the current experiment support the ide tht when lysine to CP rtio is kept constnt t 5.7, mximl productive performnce of roiler chickens to 18 dys cn e chieved mong 21 nd 25 CP. However, 25 CP diet will yield significnt lower crcss ft content. Choosing mong diets will depend on cost on the dietry protein nd consumer preferences. BIBLIOGRAFIC REFERENCES [1] ABEBE, S.; MORRIS, T.R. Note on the effects of protein concentrtion on responses to dietry lysine y chicks. Br. Poult. Sci. 31: [2] ALETOR, V.A.; HAMID, II.; NIEB, E.; PFEFFER, E. Low-protein mino cid-supplemented diets in roiler chickens: effects on performnce, crcss chrcteristics, whole-ody composition nd efficiencies of nutrient utiliztion. J. Sci. Food. Agric. 80: [3] ALLEN, N.K.; BAKER, D.H. Quntittive evlution of nonspecific nitrogen sources for the growing chick. Poult. Sci. 53: [4] ALMQUIST, H.J. Utiliztion of mino cids y chicks. Arch. Biochem. Biophys. 52: [5] ASSOCIATION OF ANALYTICAL OFFICIAL CHEM- ISTS. 15 JD Ed. Wshington, DC. 70 pp [6] BAKER, D.H. Prtitioning of nutrients for growth nd other metolic functions: efficiency nd priority considertions. Poult. Sci. 70: [7] BAKER, D.H.; HAN, Y. Idel mino cid profile for chicks during the first three weeks posthching. Poult. Sci. 73: Lysine () FIGURE 2. CARCASS FAT DEPOSITION IN BROILER CHICKENS FED LYSINE FIXED AT 5.7 OF CRUDE PRO- TEIN/ DEPOSICIÓN DE GRASA EN LA CANAL DE POLLOS DE EN- GORDE ALIMENTADOS CON LISINA FIJADA AL 5,7 DEL NIVEL DE LA PROTEÍNA CRUDA

7 Revist Científic, FCV-LUZ / Vol. XVIII, Nº 2, , 2008 [8] BARBOUR, G.; LATSHAW, J.D.; BISHOP, B. Lysine requirement of roiler chicks s ffected y protein source nd method of sttisticl evlution. Br. Poult. Sci. 34: [9] BEDFORD, M.R.; SUMMERS, J.D. Influence of the rtio of essentil to non-essentil mino cids on performnce nd crcss composition of the roiler chick. Br. Poult. Sci. 26: [10] BLUNDELL, J.E.; TREMBLAY, A. Appetite control nd energy (fuel) lnce. Nut. Res. Rev. 8: 225: [11] BREGENDAHL, K.; SELL, J.L.; ZIMMERMAN, D.R. Effect of low protein diets on growth perfomnce nd ody composition of roiler chickens. Poult. Sci. 81: [12] BUTTERY, P.J.; BOORMAN, K.N. The energetic efficiency of mino cid metolism. In : Butterworth & Co (Ed) Protein Metolism nd Nutrition, Nottinghm, UK pp [13] BUTTERY, P.J.; D MELLO, J.P.F. Amino cid metolism in frm nimls: n overview. In: J.P.F D Mello (Ed) Amino cids in Frm Animl Nutrition. 1 IJ Ed. Wllingford, UK pp [14] DENBOW, D.M. Appetite nd its control. Poult. Sci. Rev. 5: [15] D MELLO, J.P.; LEWIS, D. Amino cids interctions in chick nutrition. 4. Growth, food intke nd plsm mino cid ptterns. Br. Poult. Sci. 12: [16] EDWARDS, H.M.; FERNANDEZ, S.R.; BAKER, D.H. Mintennce lysine requirement nd efficiency of using lysine for ccretion of whole-ody lysine nd protein in young chicks. Poult. Sci. 78: [17] EITS, R.M.; KWAKKEL, R.P.; VERSTEGEN, M.W.A.; STOUTJESDIJK, P.; DE GREEF, K.H. Protein nd lipid deposition rtes in mle roiler chickens: seprte responses to mino cids nd protein-free energy. Poult. Sci. 81: [18] EMMERT, J.L.; BAKER, D.H. Use of the idel protein concept for precision formultion of mino cids levels in roiler diets. J. Appl. Poultry Res. 6: : [19] EMMERT, J.L.; EDWARDS III, H.M.; BAKER, D.H. Protein nd ody weight ccretion of chicks on diets with widely vrying contents of soyen mel supplemented or unsupplemented with its limiting mino cids. Br. Poult. Sci. 20: [20] HAN, Y.; BAKER, D.H. Lysine requirements of fst- nd slow-growing roiler chicks. Poult. Sci. 70: [21] HAN, Y.; BAKER, D.H. Digestile lysine requirement of mle nd femle roiler chicks. Poult. Sci. 73: [22] HURWITZ, S.; SkLAN, D.; TALPAZ, H.; PLAVNIK, I. The effect of dietry protein level on the lysine nd rginine requirements of growing chickens. Poult. Sci. 77: [23] KERR, B.J.; KIDD, M.T. Amino cid supplementtion of low-protein roiler diets: 1. Glutmic cid nd indispensle mino cid supplementtion. J. Appl. Poult. Res. 8: [24] LEESON, S.; SUMMERS, J.D. Protein nd mino cids. In: University ooks (Ed) 4 JD Ed. Scott s Nutrition of the Chicken. Guelph, Cnd pp [25] MACLEOD, M. G. Effects of mino cid lnce nd energy:protein rtio on energy nd nitrogen metolism in mle roiler chickens. Br. Poult. Sci. 38: [26] MORAN, E.T. Jr.; STILBORN, H.L. Effect of glutmic cid on roilers given sumrginl crude protein with dequte essentil mino cids using feed high nd low in potssium. Poult. Sci. 75: [27] MORRIS, T.R.; AL-AZZAWI, K.; GOUS, R.M.; SIMP- SON, G.L. Effects of protein concentrtion on responses to dietry lysine y chicks. Br. Poult. Sci. 28: [28] MORRIS, T.R.; GOUS, R.M.; FISHER, C. An nlysis of the hypothesis tht mino cid requirements for chicks should e stted s proportion of dietry protein. World s Poult. Sci. J. 55: [29] NIETO, R.; PRIETO, C.; FERNANDEZ-FIGARES, I.; AGUILERA, J. F. Effect of dietry protein qulity on energy metolism in growing chickens. Br. J. Nut. 74: [30] NATIONAL RESEARCH COUNCIL. Nutrient requirements of poultry. 9 JD Rev. Ed. Ntionl Acdemy Press, Wshington, DC pp [31] SKLAN, D.; PLAVNIK, I. Interctions etween dietry crude protein nd essentil mino cid intke on performnce in roilers. Br. Poult. Sci. 30: [32] STEEL, R.G.D.; TORRIE, J.H.; DICKEY, J.D. Principles nd procedures of sttistics: iomedicl pproch. 3 H@. Ed. McGrw-Hill ook CO., New York, NY pp [33] SUMMERS, J.D.; SPRATT, D.; ATKINSON, J.L. Broiler weight gin nd crcss composition when fed diets vrying in mino cid lnce, dietry energy, nd protein level. Poult. Sci. 71: