Interntionl Journl of Poultry Science 1 (1): 16-21, 2002 sin Network for Scientific Informtion 2002 Evlution of Lysine, Methionine nd Threonine Needs of roilers Three to Six Week of ge under Moderte Temperture Stress. P. Ojno-irin nd P. W. Wldroup* Poultry Science eprtment, University of rknss, Fyetteville, R 72701, US Emil: Wldroup@urk.edu strct: Informtion on mino cid requirements of roilers rised under wrm environments is very limited. Two studies of identicl design were conducted to evlute Lys, Met nd Thr needs of 3 to 6 week-old mle roilers held in ttery pens t 26.7E. sl diet ws supplemented with mino cids in 4 x 3 x 2 fctoril rrngement with Lys levels of 1.03, 1.08, 1.12, nd 1.16%, Met levels of 0.38, 0.44, nd 0.50%, nd Thr levels of 0.78 nd 0.87%. Feed consumption, ody weight (W) gin nd crcss yield were determined. Lys levels hd no significnt effect on 21 to 42 d W gin, feed conversion rtio (FR), or dressing percentge (P). Incresing Lys levels from 1.03 to 1.12% significntly (P < 0.05) improved rest yield (Y) nd reduced dominl ft. Incresing Met to 0.44% resulted in significnt improvements in W gin, FR, P, Y, nd numericl (P=0.08) reduction in F. Threonine levels used in this study hd no significnt effect on ny prmeter. There ws significnt interction of Lys nd Thr on rest yield; however it followed no consistent trend. These results suggest tht under moderte het stress, the present levels of Lys nd Met suggested y NR my e indequte for mximum live performnce or rest met yield; however, suggested levels of Thr pper to e dequte for this ge period. Key words: mino cids, roilers, temperture, het stress Introduction Methionine, lysine nd threonine re considered to e the first, second nd third most limiting mino cids in roilers fed prcticl corn-soyen mel diets, respectively. dequte dietry levels of these mino cids re needed to support optimum growth nd crcss yield of fst-growing commercil roilers. Mny poultry nutritionists use the levels recommended y the Ntionl Reserch ouncil (NR, 1994) s guideline in estlishing their own mino cid requirements, regrdless of loction nd environmentl conditions. limittion of using the NR recommendtions in wrm wether feeding is tht these levels re derived primrily from studies conducted in thermoneutrl environments nd do not indicte possile differences in mino cid needs due to environmentl tempertures. Since very little informtion is ville on the mino cid needs of roilers rised in wrm environments, nutritionists confronted with wrm wether feeding generlly dd mrgins of sfety to the NR levels. lthough the NR lso suggests incresing the mino cid levels in wrm environments to compenste for the expected reduction in feed intke, the NR noted tht this djustment should e exercised with cution since some studies hve indicted tht minimizing excesses of dietry crude protein (ustic, 1985) nd mino cids (Wldroup et l., 1976) with improved mino cid lnce my e more eneficil for roilers rised in wrm environments. In recent yers, numer of studies hve demonstrted tht elevted environmentl tempertures influence the mino cid needs of roilers, either s function of reduced mino cid digestiility (Wllis nd lnve, 1984; Zuprizl et l., 1993; Hi et l., 2000) or s result of decresed feed intke (e.g., eton et l., 1978; Howlider nd Rose, 1987). However, review of the literture shows tht very few studies hve een done to determine the mino cid needs of growing-finishing roilers rised under wrm environments. In ddition, previous studies on protein/mino cid nutrition of het stressed roilers hve shown conflicting results. Wldroup et l. (1976) showed tht minimizing dietry mino cid excesses improved growth of roilers housed in hot tempertures. Sinurt nd lnve (1985) lso suggested tht one wy of improving ody weight nd feed consumption t high temperture is to induce slight deficiency in lysine or provide lower Lys:ME rtio. series of studies conducted y heng et l. levels of 3 to 7 week-old roilers when rised ove 26.7E thus, they recommend feeding 90 to 100% of NR suggested mino cid levels. onversely, other reserchers hve reported tht het-stressed irds respond positively to incresed mino cid consumption (e.g., Fuller nd Mor, 1973; le nd Fuller, 1980). The Mrylnd roiler mino cid requirements lso indicte tht roilers rised t 80 nd 90EF need higher levels of mino cids thn irds rised t 70EF (Thoms et l., 1992). urrently, no mino cid recommendtions hve een estlished for 3- to 6-week-old roilers rised under wrm environments. Since the gretest portion of the totl feed intke is consumed during the period 3- to 6- week posthtching, meeting the ird s needs for mino cids t this growth period is necessry for economicl production. This study ws conducted to evlute the lysine, methionine, nd threonine requirements of roilers rised from 3 to 6 weeks of ge under constnt moderte temperture stress (26.7E). Mterils nd Methods irds nd Housing: Two consecutive trils of identicl design were conducted. ll nimls used in the experiments were provided proper cre nd mngement, nd without unnecessry discomfort. One-dy-old mle roiler chicks of commercil strin (o 500) were otined from locl htchery nd rndomly distriuted mong comprtments in electriclly heted ttery rooders with rised wire floors. For the first 3 weeks, the irds were fed common strter diet tht met the nutrient requirements suggested y NR (1994). t 21 d, the irds were weighed nd plced on grower experimentl diets. Six irds were rndomly ssigned to ech of 96 comprtments of wire-floored unheted grower tteries mintined in room t 26.7 E. The experimentl diets nd tp wter were provided for d liitum consumption with 24-h fluorescent lighting. iets nd Tretments: corn-soyen mel sl diet formulted ccording to NR (1994) nutrient nlysis nd mino cid compositionl vlues of yellow corn, soyen mel, nd corn gluten mel nd fortified with complete vitmin nd trce minerl mixes ws used in the study (Tle 1). It ws supplemented with sodium icronte to provide minimum electrolyte lnce [(N + K)-l] of 200 meq/kg. Sodium nd chloride levels were 0.16 nd (1997) showed no dvntge of incresing dietry mino cid 0.15%, respectively. Pulished with pprovl of the irector, rknss griculturl Experiment Sttion 16
Tle 1: omposition nd nutrient content of sl diet for The sl diet ws nlyzed for moisture, crude protein nd totl roilers 3 to 6 week-old under constnt moderte het mino cids (Llmes nd Fontine, 1994). Supplementl mino cid stress (26.7E) ssys were conducted on ll test diets (Fontine nd Eudimon, Ingredient ontent (g/kg) 2000). The levels of lysine, methionine nd threonine reported in Yellow corn 621.83 this study were djusted sed on totl mino cid ssy of our Soyen mel (SM) 255.57 sl diet nd the clculted level of dded lysine, methionine nd orn gluten mel 30.90 threonine. In generl, nlyzed vlues of dded mino cid in our niml ft 49.18 experimentl diets were in close greement to our clculted levels Limestone 16.73 (Tle 2). Monodiclcium phosphte 11.41 L-rginine 0.28 L-Isoleucine 0.05 Slt 1.75 holine hloride, 60% 2.00 Vitmin premix 2.00 Minerl premix 1.00 Sodium icronte 2.29 L-Lysine Hl (98%) 1.91 L-Methionine (98%) 1.21 L-Threonine 1.01 ntioxidnt-mold inhiitor 0.88 Totl 1000.00 Nutrient lculted nlyzed ME 3200 rude protein 19.35 20.67 lcium 0.90 Phosphorus, nonphytte 0.35 Methionine 0.32 0.38 TS 0.66 0.74 Lysine 0.95 1.03 Threonine 0.72 0.78 Tryptophn 0.24 0.18 Isoleucine 0.80 0.82 Histidine 0.51 0.56 Vline 0.90 0.88 Leucine 1.89 1.87 rginine 1.21 1.33 Glycine + Serine 1.74 1.85 Phenyllnine + Tyrosine 1.72 1.64 Provides per kg of diet: choline 1040 mg. Provides per kg of diet: vitmin (from vitmin cette) 7714 IU; choleclciferol 2204 IU; vitmin E (from dl-lph tocopheryl cette) 16.53 IU; vitmin 12 0.013 mg; rioflvin 6.6 mg; nicin 39 mg; pntothenic cid 10 mg; mendione (from mendione dimethylpyrimidinol) 1.5 mg; folic cid 0.9 mg; thimin (from thimine mononitrte) 1.54 mg; pyridoxine (from pyridoxine hydrochloride) 2.76 mg; d-iotin 0.066 mg; ethoxyquin 125 mg; selenium 0.1 mg). Provides per kg of diet: Mn (from MnSO 4. H2 O) 100 mg; Zn (from ZnSO 4. 7H2 O) 100 mg; Fe (from FeSO4. 7H2 O) 50 mg; u (from uso 4. 5H2 O) 10 mg; I (from (IO 3) 2. H2O) 1 mg. sed on NR (1994) djusted to nlyzed nutrient content of corn nd SM used in the study. The sl diet ws formulted to meet minimum of 110% of ll mino cids (NR, 1994) other thn Lys, Met, TS nd Thr (Tle 1). It ws clculted to contin 0.95% Lys, 0.32% Met, 0.65% TS nd 0.72% Thr. However, mino cid nlysis y commercil lortory indicted tht it contined 1.03% Lys, 0.38% Met nd 0.78% Thr (Tle 1). Hence, our dietry tretments were djusted ccordingly nd the lysine, methionine nd threonine levels in our dietry tretments were the ctul nlyzed vlues. From lrge lot of this sl diet, experimentl diets were mixed y supplementing liquots of the sl diet with different mounts of Lysine Hl, L-Methionine nd L-Threonine in 4 x 3 x 2 fctoril rrngement with Lys levels of 1.03, 1.08, 1.12 nd 1.16%, Met levels of 0.38, 0.44 nd 0.50%, nd Thr levels of 0.78 nd 0.87%. Ech of the 24 dietry tretments ws fed to four pens of six mle chicks from 21 to 42 d in ech of two successive trils. Mesurements: irds were group weighed y pen t 21 nd 42 d nd feed consumption during the period from 21 to 42 d ws determined. Mortlity ws checked twice dily nd weights of ded irds were used to djust feed conversion rtio (FR). t the conclusion of the study, ll remining irds were processed fter 12-h fst to determine dressing percentge, prts yield (percentge rest yield, leg qurter, wing) nd percentge dominl ft. Sttisticl nlysis: Pen mens served s the experimentl unit for ll mesurements. The results of the experiments were sujected to the nlysis of vrince (NOV) y the Generl Liner Models procedure of SS (SS Institute, 1999-2000). Significnt differences mong or etween tretment mens were seprted y repeted t-test using proilities generted y the LS mens option. ody weight t 21 d ws used s covrite for ody weight gin nlysis. ll percentge dt were sujected to rc sine trnsformtion prior to nlysis; dt presented s nturl numers. Mortlity ws nlyzed y hi-squre. The level of significnce ws sed on proility of P<0.05. Results nd iscussion The results of this study re presented in Tles 3 nd 4, nd Fig. 1. t from our experiments using typicl corn-soyen mel diets demonstrted tht dietry levels of lysine (Lys) influenced growth, ut not crcss chrcteristics of roilers grown under moderte temperture stress from 3 to 6 week of ge. In contrst, methionine (Met) levels ffected oth growth nd crcss yield, wheres threonine (Thr) supplementtion hd no significnt effect on ny prmeter. Mortlity ws low nd ws not significntly different (P>0.05) etween tretments (Tle 3). Lysine Requirement: Lys is considered s the second limiting mino cid in prcticl roiler diets fter Met nd/or TS. Lys hs no precursor role in the ody nd its utiliztion is solely for protein ccretion. ietry Lys levels evluted in this study hd no significnt effect (P>0.05) on 42 d ody weight, 21 to 42 d ody weight gin, totl feed intke, or feed conversion rtio (Tle 3). roilers fed diets with 1.16% Lys hd numericlly higher ody weight gin (1.415 kg) ut ws not significntly different (P=0.08) from the weight gin of irds fed the lower lysine levels. Sinurt nd lnve (1985) nd Hn nd ker (1993) suggested tht lysine requirement of mle roilers is not modified y high temperture. McNughton et l. (1978) conducted two experiments to evlute the lysine requirement of 2- to 4- weekold roilers mintined t 15.6 E or 29.4 E. They found tht 1.10% nd 1.0% Lys ws needed to mximize ody weight gin nd feed utiliztion of 4-week-old irds rised t 15.6 E nd 29.4 E, respectively. Using mthemticl model pproch, Hurwitz et l. (1980) predicted tht mino cid requirements of 6-week old roilers should increse t tempertures up to 27 E nd decline etween tempertures of 27 to 34 E. Under the conditions of our experiments, Lys levels from 1.03 to 1.16 % hd no significnt effect on growth performnce of mle roilers. In two different studies, Hn nd ker (1993; 1994) found tht the Lys requirement to mximize feed efficiency is higher thn to mximize weight gin. In our study we found tht under moderte het stress the lowest level of Lys tested supported mximum weight gin nd feed efficiency of 3 to 6 week-old roilers. Mrch nd iely (1972) conducted two experiments to 17
Tle 2. mount of supplementl mino cids in test diets iet Lysine Methionine Threonine --------------------------------------------- ----------------------------------------- ----------------------------------------------- lculted nlyzed lculted dded lculted nlyzed ------------------------------------------------------------------------------------------------%---------------------------------------------------------------------------------------------- 1 0 0.018 0 0.004 0 0.006 2 0 0.016 0 0.005 0.101 0.093 3 0 0.014 0.060 0.063 0 0.006 4 0 0.017 0.060 0.054 0.101 0.095 5 0 0.010 0.121 0.128 0 0.006 6 0 0.012 0.121 0.114 0.101 0.094 7 0.063 0.057 0 0.004 0 0.006 8 0.063 0.058 0 0.002 0.101 0.093 9 0.063 0.057 0.060 0.070 0 0.008 10 0.063 0.066 0.060 0.060 0.101 0.093 11 0.063 0.055 0.121 0.101 0 0.005 12 0.063 0.060 0.121 0.118 0.101 0.093 13 0.127 0.108 0 0.005 0 0.006 14 0.127 0.096 0 0.003 0.101 0.094 15 0.127 0.109 0.060 0.062 0 0.005 16 0.127 0.100 0.060 0.070 0.101 0.092 17 0.127 0.106 0.121 0.106 0 0.005 18 0.127 0.126 0.121 0.132 0.101 0.096 19 0.191 0.140 0 0.003 0 0.005 20 0.191 0.146 0 0.004 0.101 0.090 21 0.191 0.146 0.060 0.055 0 0.005 22 0.191 0.168 0.060 0.060 0.101 0.092 23 0.191 0.197 0.121 0.123 0 0.005 24 0.191 0.180 0.121 0.117 0.101 0.096. nlyzed y the method of Fontine nd Eudimon, 2000. Tle 3: Live performnce of roilers rised in constnt moderte het stress (26.7E) from 3 to 6 weeks of ge nd fed different levels of Lys, Met nd Thr Live performnce prmeters ----------------------------------------------------------------------------------------------------------------------------------------------- Tretment 42 d ody weight 21 to 42 d W gin 21 to 42 d FR Mortlity mino cid Levels (%) kg/ird kg/ird kh:kg % Lysine 1.03 2.166 1.386 1.951 1.500 1.08 2.161 1.381 1.994 1.400 1.12 2.168 1.389 1.969 1.000 1.16 2.194 1.415 1.955 2.900 Methionine 0.38 2.126 1.347 2.011 1.100 0.44 2.196 1.417 1.949 1.900 0.50 2.194 1.415 1.943 2.200 Threonine 0.78 2.163 1.384 1.965 1.200 0.87 2.182 1.402 1.971 2.200 Source of Vrition NOV P-Vlues ----------------------------- -------------------------------------------------------------------------------------------------------------------------------------------- Lys 0.347 0.082 0.126 0.396 Met <0.0001 <0.0001 <0.0001 0.580 Thr 0.197 0.192 0.680 0.230 Lys x Met 0.571 0.458 0.839 0.378 Lys x Thr 0.808 0.828 0.363 0.549 Met x Thr 0.893 0.846 0.123 0.221 Lys x Met x Thr 0.310 0.466 0.151 0.849 21 d ody Weight <0.0001 <0.0001 0.648 V 4.415 6.866 4.603 2.670 Pooled SEM 0.035 0.035 0.034 2.000 Mens of two trils with four replicte ttery pens of 6 mles per diet for ech tril. Mens within column for ech mino cid with no common superscript differs significntly t P<0.05. Men 21d wt of 780g. ody weight t 21d used s covrite. FR = feed conversion rtio, totl feed intke/ weight gin. evlute the effects of differences in energy input from oth diet nd from environmentl temperture (18.3 nd 31.1 E) on the response of chicks to diets contining different levels of Lys. They presented evidence tht incresing energy input y incresing either environmentl temperture or metolic het incresed the efficiency of feed utiliztion. In ddition, Hurwitz et l. (1980) reported tht t 27 E, the requirement for mintennce energy is minimum. This my e reson why we did not oserve different Lys needs to ttin mximl weight gin nd feed efficiency of 3 to 6 week-old roilers grown t constnt temperture of 26.7 E. Tle 4 shows the crcss composition of irds fed different levels of Lys. Lysine did not influence (P>0.05) dressing percentge, leg qurter yield or wing yield. However, incresing the dietry Lys levels from 1.03 to 1.12% significntly improved rest met yield nd reduced dominl ft (P<0.05). rest met yield (Pectorlis 18
Tle 4: rcss chrcteristics of roilers rised in constnt moderte het stress (26.7E) from 3 to 6 weeks of ge nd fed different levels of Lys, Met nd Thr Tretment rcss composition (%) --------------------------------------------------------------------------------------------------------------------------------------------------------------- mino cid Levels (%) ressed yield rest met Leg qurter Wing dominl ft Lysine 1.03 69.73 22.99 33.68 11.50 0.832 1.08 69.66 23.14 33.65 11.52 0.814 1.12 69.58 23.44 33.54 11.53 0.709 1.16 69.50 23.55 33.43 11.52 0.663 Methionine 0.38 69.37 c 22.49 33.71 11.56 0.798 0.44 69.72 23.45 33.59 11.52 0.746 0.50 69.76 23.94 33.43 11.47 0.719 Threonine 0.78 69.61 23.26 33.55 11.50 0.764 0.87 69.63 23.30 33.60 11.53 0.745 Source of Vrition NOV P-Vlues ----------------------------- ------------------------------------------------------------------------------------------------------------------------------------------- Lys 0.337 0.0001 0.177 0.841 <0.0001 Met 0.001 <0.0001 0.033 0.082 0.082 Thr 0.809 0.759 0.593 0.353 0.683 Lys x Met 0.926 0.381 0.090 0.894 0.388 Lys x Thr 0.725 0.003 0.214 0.128 0.914 Met x Thr 0.259 0.507 0.646 0.571 0.796 Lys x Met x Thr 0.767 0.453 0.425 0.917 0.757 V 1.669 3.747 2.446 2.348 42.018 Pooled SEM 0.223 0.245 0.215 0.079 0.067 Mens of two trils with four replicte ttery pens of 6 mles per diet for ech tril. Mens within column for ech mino cid with no common superscript differs significntly t P<0.05. mjor nd Pectorlis minor), expressed s percentge of the chilled synthesis of mny importnt sustnces including epinephrine, crcss weight, incresed linerly (P<0.0001) in response to choline nd cretine (ender, 1975). incresed dietry Lys levels. However, no significnt response to s shown in Tles 3 nd 4, the higher levels of Met resulted in rest met yield (P>0.05) ws oserved when dietry Lys ws significnt improvements (P<0.05) in 42 d ody weight, 21 to 42 incresed eyond 1.12%. These results support the findings of d ody weight gin, feed conversion rtio, dressing percentge, Hickling et l. (1990) nd Morn nd ilgili (1990) who reported rest met yield, nd numericl (P=0.08) reduction in tht supplementing the diet with Lys levels ove the requirement dominl ft. for mximl growth performnce resulted in incresed rest met roilers fed diets with higher levels of dietry Met hd significntly yield. In contrst, Summers et l. (1988) showed tht edile met (P<0.0001) higher ody weight nd ody weight gin thn yield ws not improved with higher levels of supplementl Lys nd roilers fed the NR Met level of 0.38% (Tle 3). However, Met. study y Mendes et l. (1997), lso found no differences further increse in Met level to 0.50% did not result in significntly in rest met yield of roilers fed 1.0 to 1.2% Lys when irds higher ody weight nd ody weight gin from those fed 0.44% were grown under hot, cyclic (25 to 33.3 E) or neutrl Met (P>0.05). The enefit of incresing Met level from NR environment (21.1 E). recommendtion to 0.44% ws 5.2% (70 g per ird) increse in The increse in crcss ft of roilers rised under hot mient 21 to 42 d ody weight gin while weight gin of irds fed 0.44 temperture is nother concern since the ft content of met nd 0.50% Met were the sme. The higher levels of Met dded to products hs ecome incresingly importnt to consumer the diets lso resulted in significntly improved feed conversion perceptions of the helthfulness of met. Previous studies hve rtio (P<0.0001). gin, there ws no significnt difference shown tht irds grown under hot environment tend to hve etween irds fed 0.44% Met nd 0.50% Met (Tle 3). higher dominl ft (Howlider nd Rose, 1987; in ziz et l., In our evlution on the effects of Met levels on crcss 1996; Mendes et l., 1997). Hussein nd l-tshn (1999) nd composition of 3- to 6-week-old roilers under moderte het Mendes et l. (1997), found tht incresing dietry lysine in diets stress (Tle 4), we oserved significnt improvements (P<0.05) of het-stressed 3 to 6 week-old roilers significntly reduced in dressing percentge nd rest met yield etween the roilers dominl ft. Similrly, we found tht incresed Lys fed NR Met level nd those fed higher levels. irds fed diets with supplementtion resulted in significnt (P<0.0001) liner reduction 0.44% Met hd significntly higher dressing percentge (P<0.001) in dominl ft content, expressed s percentge of the chilled thn did irds fed diets with 0.38% Met; dressing percentge did crcss weight. irds fed 1.03% nd 1.08 Lys hd greter not differed etween those fed 0.44% nd 0.50% Met. percentge of dominl ft thn those fed 1.12 or 1.16% Lys. rest met yield incresed linerly (P<0.0001) with incresing gin, no significnt differences were oserved etween the two Met level. Feeding irds diets with 0.44% Met resulted in 0.96% higher Lys levels (P>0.05). increse in rest met yield compred to those fed NR level. Our results nd those of other uthors suggest tht the current further increse in Met supplementtion to 0.50% only resulted in NR (1994) recommendtion of 1.0% Lys for 3- to 6- week-old nother 0.49% improvement in rest met yield. Methionine roilers is dequte to support comprle growth performnce levels lso significntly influenced leg qurter yield (P<0.05) with ut higher level (1.12%) is needed to otin optimum rest the optimum yields t 0.44% Met. The tendency of leg qurter met yield nd reduced dominl ft if irds re grown from 3 to yield to decrese with incresing Met my not e tretment 6 weeks of ge under moderte temperture stress. effect. It cn e ttriuted to the fct tht prts yield re expressed s percentge of the whole crcss. Therefore, leg Methionine Requirement: Met, the first limiting mino cid in roiler qurter decresed s rest met yield incresed. lthough there diets, hs numerous functions in the ody. It serves s n integrl ws trend for dominl ft, expressed s percentge of the portion of ody protein, is precursor for cystine, nd n chilled crcss weight, to decrese linerly with incresing dietry importnt source of dietry sulfur. S-denosyl methionine is Met supplementtion, it ws not significntly different etween potent donor of methyl groups, which contriutes to the the three Met levels evluted herein (P=0.08). 19
Interctions: The only significnt interction tht we oserved in our study ws tht of Lys nd Thr on rest met yield (P<0.05). However, it followed no consistent trend, with the higher level of Thr significntly improving rest met yield t some levels of Lys nd significntly decresing rest met yield t other levels of Lys (Fig. 1). Kidd et l. (1997) lso oserved n interction etween Lys nd Thr on rest met yield nd found no consistency either. In contrst, Kerr et l. (1999) reported tht Lys nd Thr intercted on rest met weight so tht 100% of the NR Thr level ws required to mximize rest met in roilers fed the 105% Lys diet, nd 107.5% Thr ws necessry to mximize rest met in roilers fed the 120% Lys diets. The present study demonstrtes tht under conditions of moderte temperture stress, supplementing the diet of roilers for the period from 3 to 6 weeks of ge with 0.44% Met resulted in significnt improvements in ody weight gin, feed conversion rtio, dressing percentge nd rest yield. Feeding het-stressed roilers diets with Lys level from 1.03 to 1.16% did not influence Fig. 1: Lysine nd threonine interctions on rest met yield of growth prmeters; however, higher level (1.12%) ws needed 42-d old mle roilers rised in constnt moderte het to increse rest met yield nd reduce dominl ft. Growth stress (26.7E) from 3 to 6 weeks of ge nd crcss yield were not ffected y Thr concentrtions of 0.78 Mens of two trils with four replicte ttery pens of 6 mles nd 0.87%. n interction etween Lys nd Thr level on rest per diet for ech tril. met yield ws oserved ut showed no consistent trend. -d rs with no common superscript for ech threonine level differ significntly (P<0.05). onclusions: roilers grown under constnt moderte temperture stress (26.7E) from 3 to 6 weeks of ge fed cornto The Met level found dequte for optimum growth performnce soyen mel diet with 3250 kcl/kg ME need 0.44% methionine nd met yield of 3 to 6 week-old mle roilers rised under moderte temperture stress ws higher thn the NR recommended level of 0.38% nd vlues oserved y previous studies. ccording to heng et l. (1997), het- stressed roilers from 3 to 6 weeks of ge should not e fed diets with crude protein (P) greter thn 20 nd 100% NR mino cid levels since such prctices my led to more detrimentl effects. Moreover, they reported tht supplementing 16 nd 18% P diets with Met, Lys, Thr, Trp, nd rg to provide 100 to 110% NR levels did not improve weight gin of het-stressed roilers compred to those fed 90% NR level. lnve nd Oliv (1990) chieve optimum ody weight gin, feed conversion rtio, dressed yield nd rest met yield. further increse in dietry Met level to 0.50% did not result in significnt improvements in growth nd crcss prmeters. ody weight gin nd feed conversion rtio of mle roilers under moderte temperture stress nd fed diets with lysine level from 1.03 to 1.16% ws not significntly different. However, higher level (1.12%) ws necessry to increse rest met yield nd reduce dominl ft. Feeding diets with threonine levels of 0.78 nd 0.87% hd no significnt effects on growth or crcss qulity of 3 to 6-week-old exmined the responses of finishing roilers t high temperture mle roilers kept constntly t 26.7 º. rest met yield of hetstressed roilers ws significntly influenced y n interction of to dietry Met source nd supplementtion levels. These uthors concluded tht the methionine requirement for 3 to 6 week-old Lys nd Thr ut ws without consistent trend. The higher level mle roilers decresed from 1.21 g/mcl ME t 21 E to 1.09 of Thr improved rest met yield t some levels of Lys nd decresed rest met yield t other levels of Lys. g/mcl ME t diurnlly cycling tempertures of 25 to 35 E nd 0.92g/Mcl ME t constnt high temperture (30E). Threonine Requirement: In prcticl roiler diets, Thr is considered s the third limiting mino cid fter Met nd Lys. Thr serves s component of ody protein, plys n importnt role in fether synthesis s component of fether protein nd precursor of glycine nd serine, is involved in immune responses, needed in gstrointestinl mucin production, nd it hs een shown to improve livility of het-stressed roilers (Lemme, 2001). ietry threonine levels hd no significnt effect (P>0.05) on growth or crcss prmeters evluted in this study (Tle 3 nd 4). s the lowest level exmined ws in excess of the NR (1994) recommendtion we cnnot determine if Thr levels recommended y NR re dequte or extr Thr eneficil under moderte het stress. In the lst decde, severl studies hve een conducted to evlute the Thr requirement of growing roilers. The mjority of these studies (e.g., Thoms et l., 1986; Weel et l., 1996; Kidd et l., 1997; Kidd nd Kerr, 1997) lso indicte tht NR Thr level for the 3- to 6- week growth period is dequte or more thn dequte. In review of the literture, Lemme (2001) reported tht depending on the performnce criteri chosen, the optimum dietry Thr levels for 20- to 42-d-old roilers to chieve 95% of the symptotic response for ody weight gin, feed conversion rtio nd rest met yield were 0.66, 0.68 nd 0.70%, respectively, compred to the 0.74% suggested y NR (1994) for 21 to 42 d-old roilers. cknowledgement The uthors would like to thnk jinomoto Hertlnd, Inc., hicgo, IL 60631 for conducting the mino cid ssy of the diets used in the experiments. References in ziz, H., P.. Gerert, J..F. Pdilh nd S. Guillumin, 1996. hronic het exposure enhnces ft deposition nd modifies ft prtition in roiler crcsses. Poult. Sci., 75:505-513. ustic, R.E., 1985. Feeding poultry in hot climtes. Pges 123-136 in: Stress Physiology in Livestock. M.K. Yousef, ed. R Press, oc Rton, FL. lnve,. nd. Oliv, 1990. Responses of finishing roilers t high tempertures to dietry methionine source nd supplementtion levels. ust. J. gric. 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