Intrntinl Jurnl f Pultry Sin 5 (2): 185-190, 2006 ISSN 1682-8356 Asin Ntwrk fr Sintifi Infrmtin, 2006 Efft f Chrni Ht Strss n Lng-Trm F Rstritin n Brilr Prfrmn Z.H.M. Au-Diyh Dprtmnt f Agriulturl Sins, AL-Shuk Univrsity Cllg, Al-Blq Appli Univrsity, M`n Al-Shuk, Jrn Astrt: An xprimnt ws nut t invstigt th ffts f lng-trm f rstritin n llviting th ffts f hrni ht strss n th prfrmn f 4-8-wk l ISA Vtt rilr irs. Envirnmntl tmprturs wr nstnt 25, n 35±2 C in ntrll nvirnmntl rms n vril-nturl tmprtur rng twn 21 n 30±2 C in n pn-si pultry hus. At 4 wks f g, Dily f nsumptin in ll xprimntl rms ws rstrit t 75% n 50% f th ily liitum nsumptin rmmn in th mngmnt gui fr this strin. At th n f xprimnt, rprsnttiv smpl f 8-wk-l rilrs frm h trtmnt ws slt n pl rnmly in ntrll-nvirnmntl hmrs st t 40±1 C fr ht tlrn tst. Th rsults shw tht, rring tmprtur f 35±2 C in ls nvirnmnt n vril-nturl tmprtur f 21-30 ± 2 C in th pn-si nvirnmnt h signifint (p<0.05) ngtivly ffts n rilr prfrmn. Lng-trm f rstritin t 75% r 50% ru signifintly (p<0.05) th grwth rt n y gin f 4-8-wk l rilrs. Th y wight gin f irs rr t 35 C n f 50% f liitum ws highr thn thir untrprts rr t nstnt 25 C r vril-nturl tmprtur (21-30 C). F nvrsin rti n survivility wr signifintly (p< 0.05) imprv with inrsing f rstritin t high mint tmprtur f 35± C. Hwvr, f rstritin t lwr mint tmprtur f 25 C h ngtiv ffts n f nvrsin rti. On th thr hn, ht tlrn tst shw tht, f rstritin imprv ht tlrn n inrs th ht rsistn f 8- wk l rilrs whn xps t 40 C. Lwr mrtlity rt n lwr rt f inrs f rtl tmprtur f f rstrit irs init this. Frm th rsults f this xprimnt, it ul nlu tht, mint tmprtur n lng-trm f rstritin signifintly fft rilr prfrmn. Mrvr, lng-trm f rstritin t high mint tmprtur inrs ht rsistn n imprv th ht tlrn f grwing rilrs, whn xps t ht wvs in summr ssn. Ky wrs: Brilr prfrmn, f rstritin, ht strss, ht tlrn Intrutin Th xprssin f ht strss in pultry prutin n sri s ut r hrni ; ut ht strss rfrs t shrt n sun pris f xtrmly high tmprtur, whr s hrni ht strss rfrs t xtn pris f lvt tmprtur (Emry, 2004). On th thr hn, nitins f ht strss us n inrsing nrn in pultry prutin u t th rpi vlpmnt f pultry inustry in htlimt untris n t th ru prfrmn f pultry uring summr mnths in tmprt untris (Bnnt t l., 1997). It hs n shwn tht ht strss hs trimntl ffts n th prfrmn f 4-8 wk l rilr irs rr in th pn-si pultry huss; priniplly thrugh ruing f intk, grwth rt, ngtivly fft f ffiiny n rss qulity s wll s hlth (Crmn t l., 1991; Yhv t l., 1996; Tmim t l., 2000; Hr t l., 2000; Oskn t l., 2003). Mrvr, hrni ht strss inrss th tim t rh mrkt wight n inrs mrtlity rt (Hwlir n Rs, 1989; Ozy n Ozilik, 2004). F rstritin uring th pris f ht strss hs m mmn mngmnt prti in mny rilr-pruing rs (Kh n Ml, 1999; Oskn t l., 2003). Lwring f intk n lwr th y tmprtur f th ht-xps rilr irs n inrs its ility t surviv ut ht strss (Li t l., 1992; Wirnusz n Ttr, 1996; Kh n Ml, 1999). Bnfiil ffts f shrt-trm fsting n rilr prfrmn prir t ut ht strss hv n xtnsivly rviw. Hwvr, thr is lss infrmtin n th ffts f lng-trm f rstritin n rilrs rr unr summr nitins tht my imps hrni ht strss (Oskn t l., 2003). In itin, mst prvius f rstritin-thrml nvirnmnt stuis wr nut unr shrt-trm fsting t yli r nstnt-ut ht strss nitins in ls nvirnmnt nithr xplin nr mpr th ffts f vril-nturl with nstnt-hrni high rring tmprturs n rilr prfrmn. Thrfr, th jtivs f this stuy wr t invstigt th ffts f lng-trm f rstritin n llviting th ffts f nstnt-hrni ht strss n vril-nturl tmprturs n th prfrmn f 4-8 wk l rilrs rr in ls n pn-si huss. 185
Au-Diyh: Efft f Chrni Ht Strss n Lng-Trm F Rstritin n Brilr Prfrmn Mtrils n Mths Exprimntl rms Cntrll nvirnmntl rms: A ntrll nvirnmntl pultry hus nsists f 2 intil rms ws us in this stuy. Eh rm ws ivi int 6 intil pns msur 0.88 x 2.40 m. suppli with trugh fr n utmti-up rinkr. Eh rm ws quipp with thrmsttilly ntrll ltri htrs n n ltri fn fr th irultin f ir. Air is rmv frm th rms y th prsn f n xhust fn in th k r f th rm. Rltiv humiity ws unntrll insi th rms, it ws rng twn 36-50% uring th xprimntl pri. Cntinuus rtifiil light ws us t illumint th intrir sp uring th xprimntl pri, whih ws lst fur wks. Opn-si pultry hus: An pn-si pultry hus us ntin 6 intil rms. Eh rm ws ivi y wir msh int tw qul pns msur 2.20 x 4.10 x 3.50-m. Eh pn ws suppli with trugh fr n utmti up rinkr. Artifiil light, uring th night ws us whih ws ntrll y th utmti-lk timr swith n t 00190 hr n ff t 0500 hr uring th mrning tim. Envirnmntl nitins insi th hus wr nt ntrll n thus vri with th utsi nturl nitins. Cntrll-nvirnmntl hmrs: Tw ntrll nvirnmntl hmrs wr us fr ht tlrn tst f 8-wk l rilrs t 40±1 C. Th imnsins f th tw hmrs r 2.70 x 2.10 x 2.34 m n 1.80 x 2.40 x 2.34 m, rsptivly. Eh hmr ws quipp with thrmsttilly ntrll ltri htrs n n ltri fn fr th irultin f ir. Tw hls f 16-m imtr in th sis f th hmr wr m t prvi vntiltin. A ttry f 8 iniviul gs rrng in tw rws, wr instll insi h hmr. Eh g msur 37x30x40 m, n suppli with sprt rinkr n fr. Amint tmprtur n ntrll t th ury f 40±1 C. Exprimnt: Six hunr ISA Vtt y-l rilr hiks wr tin frm mmril hthry n rr frm n y t 4 wks f g s grup using th stnr ring prtis. Thy wr rr n littr with f n wtr prvi liitum. Thy wr f stnr strtr it frm 0 t 4 wks f g (Tl 1). At fur wks f g ttl f 480 ISA Vtt grwing rilrs wr wigh n mv t rnm t th xprimntl rms. Thr nvirnmntl tmprturs wr us, 25 ± 2 C, 35 ± 2 C with rltiv humiity f 41-50 % in th ntrll nvirnmntl rms, n 21-30 C nturl vril tmprtur, with rltiv humiity f 36-42% in th pn-si pultry hus. Brilr trtmnts in h tmprtur rm wr sign t rstrit f intk y rstriting th munts f f tht th irs wr llw t nsum h y. Brilrs in h rm wr f liitum, 75, n 50% f th ily f intk munts rmmn in th mngmnt gui fr this strin (Institut Sltin Animl, ISA, 1989). F intk lvls wr just t liitum munts rmmn in th mngmnt gui t mk th mprisn twn th rilr f trtmnts t iffrnt mint tmprturs is pssil. Th ttl munts f f intk ffr t rilrs t iffrnt mint tmprturs wr 1782.5, 2674, n 3565, grm/ir fr (50%AL), (75%AL), n liitum (AL) trtmnts, rsptivly (Institut Sltin Animl, ISA, 1989). Wtr ws prvi fr liitum nsumptin. Thy wr kpt unr xprimntl nitins thrughut th xprimntl pri frm 4 t 8 wks f rilr g. Th xprimntl trtmnts wr 3 lvls f f x 3 nvirnmntl tmprturs. Thr wr 2 rplits f 20 irs h, in th ntrll nvirnmntl rms, n 2 rplits f 40 irs h, fr h trtmnt in 2 th pn-si rms with 10 irs/m. All th mns f xprimntl trtmnts wr nlyz y ANOVA using th gnrl linr ml (GLM) prur f sttistil nlysis systm (SAS) (SAS Institut, 1987). Whn signifint F sttisti ws nt, trtmnt mns wr sprt using Dunn s multipl rng tst. Sttmnts f signifint iffrn r s n f P = 0.05. Ht tlrn tst: This tst ws nut t invstigt th ffts f rring-mint tmprtur n f rstritin rgims n th ht tlrn tim n rt f inrs f rtl tmprtur (RITr) f 8- wk l rilrs whn xps t ut ht strss f 40±1 C. At th n f th fur wks f th xprimnt, rprsnttiv smpl f 8-wk l rilrs ws rnmly slt frm h trtmnt n mv t th nvirnmntl physilgy l whr th tw ntrll nvirnmntl hmrs st t 40 ±1 C. Th rilr smpls wr mrk n rnmly pl int th hmrs n kpt t 40±1 C until th rtl tmprtur rh ut 45 C r th ur. Rtl tmprtur f th rilr smpls ws msur fr th ginning f th tst n thn t hurly intrvls, r mr frquntly if pprh 45 C, using n ltri-thrmupl thrmmtr insrt pprximtly 3 m urt t 0.1 C (Ylin t l., 2001). N f r wtr ws ffr uring th tst. Th inrsing rt f rtl tmprtur (RITr) uring th tst pri ws lult y iviing th hng f rtl tmprtur ( C) n th tim pri (hurs) spnt until rtl tmprtur rh 45 C r th ur. Syks n Alftfth (1987) us this xprssin s n initr f ht tlrn imprvmnt. 186
Au-Diyh: Efft f Chrni Ht Strss n Lng-Trm F Rstritin n Brilr Prfrmn Tl 1: Ingrints n lult mpsitin f th sl wight s illustrt in Tl 2. Th y wight gin f its irs rr t 35 C n f liitum ws signifintly Ingrints n mpsitin Strtr (%) Finishr (%) (p<0.05) lwr thn ths rr t 25 C r 21-30 C Yllw Crn 63.80 72.20 whn mpr t th 4 wks f xprimnt. Hwvr, Sy n ml (44% CP ) 28.00 21.50 f rstritin t 75% r 50% f liitum inrs Fish ml (72% CP ) 5.00 3.00 Lim stn 1.60 1.60 ht tlrn f irs rr t 35 C. Sin, thr wr Dilium phspht 1.00 1.20 n signifint iffrns in th ttl y gin whn Prmix (Vitmin + Minrls ) 0.10 0.10 mpr with thir untrprts rr t 25 C. Th DL-Mthinin 0.20 0.10 y wight gins f irs rr t 35 C n f 50 % Sium Chlri 0.30 0.30 r 75% f liitum wr 784 n 1091 grm/ir Ciistt 0.05 0.05 rsptivly, vrsus 754.5 n 1161 f irs rr t Clult Anlysis Mtlizl Enrgy (kl/kg) 2921 2994 25 C. Ths rsults r in grmnt with th rsults Cru Prtin% 21.40 18.10 tin y Kh n Ml, (1999) wh fun tht, th Lysin% 1.19 0.93 y wight f rilrs rr t 32, 27, 22, n 17 C Mthinin% 0.55 0.33 ws rs signifintly with rsing f intk Mthinin n Cystin % 0.89 0.62 t 75, 50, n 25% f liitum nsumptin. In Clium% 1.09 1.08 itin, Ourt t l. (1989) fun tht irs rr in ht Ttl Phsphrus% 0.98 0.68 nvirnmnt (32 C) fr 4.7 hur/y n fst 10 hur/y h signifintly (p < 0.05) lwr y wight Rtins: Stnr rilr strtr n finishr its wr hngs thn ths unht n full f liitum f frm 0 t 4 n 5 t 8 wks f g, rsptivly, r nsumptin. shwn in Tl 1. It supplis th rquir nutrints Mns ±S.E f f nvrsin rti f rilrs rr t rmmn in th mngmnt gui f ISA Vtt iffrnt mint tmprturs n f iffrnt fing rilr strin us in this xprimnt (Institut rgims r shwn in Tl 2. Th rsults shw lrly Sltin Animl, ISA, 1989). th fft f inrsing nvirnmntl tmprturs n f nvrsin rti. F nvrsin rti f irs Rsults n Disussin rr t 35 C n f liitum ws signifintly Brilr prfrmn: Mns±S.E f liv prfrmn highr thn ths rr t 25 C n ls highr thn prmtrs f rilrs rr t iffrnt nvirnmntl ths t 21-30 C. In gnrl, liitum f irs rr tmprturs n thr fing rgims r shwn in in ht nvirnmnt (35 C) hiv th prst f Tl 2. Th y wight f rilrs f liitum n ffiiny n thy wr lss ffiint in f utiliztin rr t 35, 25 C n nturl (21-30 C) r signifintly thn irs rr in lwr mint tmprturs (25 C (p < 0.05) highr thn thir untrprts f 50 r 75% f th liitum nsumptin. Th rsults ls shw n nturl 21-30 C). Ths rsults r similr t th finings f prvius rsrhrs (MDwll, 1972; tht, fing rgim fft th y wight Hrris t l., 1974; Yhv t l., 1996; Ozy n signifintly (p < 0.05). At th n f th fur wks f th xprimnt, th y wight f rilrs in ll ht trtmnts rs signifintly (p< 0.05) s fing rgim ru frm liitum t 75% n 50% f th liitum nsumptin. Brilrs f liitum t th mint tmprtur f 25 C h highr y wight thn ths t 21-30 C, ut signifintly (p< 0.05) highr thn ths rr t 35 C. This fining is nsistnt with th srvtins f Ozy n Ozilik (2004); Oskn t l. (2003) n AuDiyh (2006). Th inrs in ht tlrn f irs y rstrit fing ws lrly illustrt y th rsults tin. Th y wight f th irs rr t 35 C n f 50% t th n f th fur wks f th xprimnt ws 1375 grm vrsus 1334 grm fr th irs rr t 25 C. This iffrn ws signifint t (p< 0.05) lvl, whil rstritin f f t 75% h smllr fft n ht tlrn mpr with 50% lvl. Ths rsults r in grmnt with th rsults tin y (Zulkifili t l., 1994; Hking t l., 1996; Kh n Ml, 1999). Ozilik, 2004; Au-Diyh, 2006). F rstritin h psitiv fft n th f nvrsin rti f irs rr unr ht nvirnmnt (35 C) t th furth wk f th xprimnt. It ws 2.27, 2.45, n 2.60 fr irs f 50%, 75% n liitum, rsptivly. This is lr initin f imprv ht tlrn f irs y f rstritin. Hwvr, f rstritin t lwr mint tmprturs 25 C h ngtiv ffts n f nvrsin rti. In th pnsi rm t nturl vril tmprtur (21-30 C), thr wr signifint (p<0.05) iffrns in th vrg f nvrsin rti f th liitum irs n ths rstrit t 75% f liitum nsumptin. F nvrsin rti f f-rstrit irs ws lwr thn th vrg f nvrsin rti f liitum irs. This fining is nsistnt with th srvtins f Plvnik n Yhv (1998). Th imprvmnt in f ffiiny ssit with f rstritin t 35 C hs n ttriut t highr mtli ffiiny ssit with mintining Th trn in y wight gin ws th sm s th y smllr y wight. At th nturl vril tmprtur 187
Au-Diyh: Efft f Chrni Ht Strss n Lng-Trm F Rstritin n Brilr Prfrmn Tl 2: Mns ±S.E f liv y wight, y gin, f nsumptin, f nvrsin rti (FCR), n mrtlity rt f 8 wk-l rilrs rr t iffrnt mint tmprturs n f iffrnt fing rgims Prfrmn prmtr Trtmnts --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Vril-Nturl Tmprtur (21-30 C) Cnstnt-Chrni Amint Tmprtur 25 C Cnstnt-Chrni Amint Tmprtur 35 C -------------------------------------------------------------- ----------------------------------------------------------------- ------------------------------------------------------------------ A liitum (AL) 75% (AL) 50% (AL) A liitum (AL) 75% (AL) 50% (AL) A liitum (AL) 75% (AL) 50% (AL) Liv By Wight (grm/ir) 2050 ±21 1807.5 ±44 g 1321 ± 20 2107 ± 35 1755 ± 0.0 g 1334.5 ±38 1847.5 ±30 1716.5 ±5.0 f 1375 ± 0 Liv By Gin (grm/ir) 1358 ± 50 1218 ± 67 716.5 ±23 1544 ±19 1161 ±94 754.5 ±54 1178 ±43 1091.5 ±4.0 784 ±23 F Cnsumptin (grm/ir) 3535 2673 1784 3418 2673 1784 3042.5 2673 1784 F Cnvrsin Rti (FCR) 2.59 ±.06 2.19 ±.10 2.49 ±.10 2.19 ±.02 2.29 ±.02 2.32 ±.20 2.60 ±.10 2.45 ±.05 2.27 ±.10 Mrtlity Rt (%) 3.62 ±3.0 2.22 ±0.0 1.11 ±1.0 0.00 ±0.0 0.00 ±0.0 5.13 ±5.0 12.9 1 ±0.0 5.00 ±0.0 0.00 ±0.0 Mns with iffrnt suprsripts in th sm rw r signifintly iffrnt t (p < 0.05). Tl 3: Mns ±S.E f rtl tmprtur ( C) f rilrs rr t iffrnt mint tmprturs n f iffrnt fing rgims uring th pris f xprimnt 2. Trtmnts ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Wks Vril-Nturl Tmprtur (21-30 C) Cnstnt-Chrni Amint Tmprtur 25 C Cnstnt-Chrni Amint Tmprtur 35 C ---------------------------------------------------------- --------------------------------------------------------------- -------------------------------------------------------------- A liitum 75%(AL) 50%(AL) A liitum 75%(AL) 50%(AL) A liitum 75%(AL) 50%(AL) (AL) (AL) (AL) 1 40.90 ±0.0 41.05 ±0.1 40.6 ±0.2 40.85 ±0.1 40.90 ±0.0 40.95 ±0.1 42.05 ±0.1 41.45 ±0.2 40.75 ±0.2 2 41. 00 ±0.2 40. 9 ±0.1 40.6 ±0.0 40.85 ±0.1 40.8 5 ±0.1 40.7 ±0.0 41.6 ±0.3 41. 4 ±0.2 40.55 ±0.1 3 41.25 ±0.5 40.85 ±0.1 40.75 ±0.1 40.8 ±0.0 40.95 ±0.1 40.75 ±0.1 42.25 ±0.2 41.45 ±0.2 40.55 ±0.1 4 41.0 ±0.1 41. 2 ±0.2 40.80 ±0.1 41.05 ±0.2 41. 2 ±0.1 40.8 ±0.1 41.95 ±0.1 41.35 ±0.1 40.8 ±.01 Mns with iffrnt suprsripts in th sm rw r signifintly iffrnt t (p< 0.05). Tl 4: Mns ±S.E mrtlity rt (%), n rt f inrs f rtl tmprtur RITr, ( C/ hur) f 8-wk l rilrs xps t 40 C t th n f xprimnt. Rring Amint Tmprturs ( C ) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Vril-Nturl Tmprtur Cnstnt-Chrni Amint Tmprtur Cnstnt-Chrni Amint Tmprtur (21-30 C) 25 C 35 C --------------------------------------------------- ------------------------------------------------------ ------------------------------------------------------- A liitum 75% 50% A liitum 75% 50% A liitum 75% 50% Prmtr msur (AL) (AL) (AL) (AL) (AL) (AL) (AL) (AL) (AL) Mrtlity rt (%) 75 ±19 25 ±19 0.0 19 88 ±19 50 ±19 12 ±19 13 ±19 0.0 ±19 0.0 ±19 RITr 3.9 ±0.6 3.0 ±0.6 2.1 ±0.6 3.9 ±0.6 3.3 ±0.6 3.6 ±0.6 2.1 ±0.6 2.70 ±0.6 2.40 ±0.6 Mns with iffrnt suprsripts in th sm rw r signifintly iffrnt t (p<0.05). 188
Au-Diyh: Efft f Chrni Ht Strss n Lng-Trm F Rstritin n Brilr Prfrmn (21-30 C), th vrg f nvrsin rti f rilrs rsults illustrt th fft f rring mint rstrit t 75% f liitum nsumptin is insignifintly lwr thn th rrspning grups rr t 25 n 35 C. In lyr hns, Li t l. (1992) fun tht th rt f ht prutin rs ntinuusly with inrsing nvirnmntl tmprtur t ny f nsumptin lvl. Th rs in ht prutin with inrsing nvirnmntl tmprtur rsult in rutin f nrgy rquirmnts. Th rts f hng in ht prutin with tmprtur tn t inrs with th rutin in f nsumptin, whih inits tht th ptiml tmprtur fr nrgy ffiiny inrss with rsing f nsumptin. Rring rilrs t high mint tmprturs (35 C) us signifint inrs in mrtlity rt s shwn in Tl 2. F rstritin f rilrs kpt t high mint tmprtur (35 C) ru signifintly th mrtlity rt. Th ttl mrtlity rts t 35 C wr 12.19, 5.0 n 0.0% fr rilrs f liitum, 75 % n 50 %, rsptivly. Th sm trn ws ls illustrt fr rilrs rr t th nturl trtmnt. Th rutin f mrtlity rt inits tht f rstritin rus th fft f ht strss n rilr prfrmn. Survivility ws ssit with lwr f nsumptin n y wight n ws ssit with lwr mtli ht prutin thrughut th xprimntl pri, whih rus th susptiility t ht strss. Th inrs in ht tlrn might u t rs in ht prutin s rsult f f nsumptin. (Li t l., 1992; Wirnusz n Ttr, 1996). Lwr rtl tmprturs s shwn in Tl 3 init this. In gnrl, f rstritin t 50 n 75% f liitum nsumptin ws ssit with lwr rtl tmprtur f rilrs kpt t th thr mint tmprtur trtmnts. This fining is nsistnt with th srvtins f Altn t l. (2003); Ozy n Ozilik (2004) n Au-Diyh (2006). Th lwr Tr t 35 C rflts th inrs f ht tlrn f irs s rsult f f rstritin. Thus, f rstritin frm 75 t 50% f liitum imprv signifintly th ht tlrn f rilrs prtiulrly in th lst wks f rring pri. Ths rsults ul xplin tht f rstritin ws ssit with lwr mtli ht prutin whih l t rutin in ht l n susquntly Tr i nt inrs n ws mintin within nrml limits (Nrth n Bll, 1990). This is lr initin tht f rstritin imprv ht tlrn f rilrs uring xpsur t hrni ht strss. This is nfirm y th rsults f Kh n Ml (1999) wh fun tht, rtl tmprtur f rilrs ws inrs signifintly whn f intk lvl ws inrs frm 25, 50, 75% f liitum nsumptin. Ht tlrn tst: Mns f mrtlity rt, n th rt f inrs f rtl tmprtur (RITr) f rilrs uring th ht tlrn tst t 40 C r shwn in Tl 4. Th tmprtur n f rstritin n imprving ht tlrn f 8-wk l rilrs whn xps t mint tmprtur highr thn th rring tmprturs. F rstritin imprv ht tlrn signifintly, prtiulrly t th 50 % lvl in th iffrnt ht trtmnts. Th rsults illustrt th imprtn f f rstritin n rring mint tmprtur n ruing grt lsss uring xpsur t ht wv. Als, inrsing th ht tlrn ws xprss in lwr rt f inrs f rtl tmprtur (RITr). RITr f rilrs rr t 35 C ws insignifintly lwr thn thir untrprts rr t 25 C r nturl (21-30 C). Als, f rstritin t 35 C rsult in lwr rt f inrs f rtl tmprtur, whih is n initin f imprv ht tlrn. This fining is nsistnt with th srvtins f Zulkifili t l. (2000) wh fun tht, th survivility f fml rilrs rstrit t n rly g t 60% f liitum nsumptin ws signifintly (p < 0.05) highr thn liitum rilrs whn xps t ht tlrn tst t 38 C. Ths rsults init tht th uppr ritil tmprtur ul inrs t high rring tmprtur n f rstritin. Crmn t l. (1991) fun tht, whn irs wr xps fr 4 hurs t 38 C withut f h signifintly (p<0.05) lwr rt f inrs f rtl tmprtur n th rtl tmprtur ttin ftr 4 hurs f ht xpsur ws 41.2 C mpr with th ntrl grup xps with vill f. This is u t prir ht limtiztin n lwr ht prutin f th irs. Ttr n Smith (1986) rprt tht, t lst 50% f th hyprthrmi fft f limtiztin immitly prir t ht strss might ttriut t rutin in f intk in rspns t th strss. Ht limtiztin is rught ut y rutin in ht prutin rthr thn y n inrs in ht lss. Mrvr, Ltt (1991) fun tht, limt rilrs t 35 C h signifintly (p < 0.05) lwr rtl tmprtur thn unlimt irs riv f 1 hur prir t xpsur t 24-41 C. This is nfirm y th rsults f Syks n Alftfth (1986) wh fun tht, th filur t limtiz fllwing trnsfr f irs frm ht (30) t l (20) nvirnmnt ws u t n inrs in f intk n ht prutin. Finlly, it ul nlu frm th ll rsults f this xprimnt tht, hrni ht strss n lng-trm f rstritin signifintly fft rilr prfrmn. Thus, full-f rilrs rr in pn-si nvirnmnt uring summr ssn n lngr tim thn mrt nitins t hiv th sm y wight. Susquntly, th mrkt g will lngr. Mrvr, Lng-trm f rstritin f ht strss rilrs is nt nly rspnsil fr pr prfrmn, ut ls, it inrs ht rsistn n imprv th ht tlrn f grwing rilrs whn xps t ht wvs uring summr ssn. 189
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