Review:EnergypartitioninginbroilerchickensG. LopezandS. Leeson1DepartmentofAnimal &PoultryScience,UniversityofGuelph,Guelph,Ontario,CanadaN1G2W1.Received12July 2007, accepted20February 2008.Lopez, G. andLeeson, S. 2008. Review: Energypartitioninginbroiler chickens. Can. J. Anim. Sci. 88: 205212. Incommercial nutritionandinresearchstudies, metabolizable energy(ME) is the standardmeasure of energyusedindescribing energy requirements and diets for poultry. The provision of dietary energy will influence the intake of all othernutrients. Broilers exhibit an outstanding ability to control their energy intake by adjusting their feed intake as diet energyconcentration changes. There is still considerable debate on the accuracy, precision and usefulness of different proceduresusedfor determiningME valuesofdiets and ingredients.ME intakeisgenerallypartitionedinto energyretained(ER)inbody tissues (mainly as fat and protein) and as heat production (HP): MEHPER. There are few reported estimates ofHP and its components, fasting heat production (FHP), heat production due to physical activity and the thermic effect offeeding(TEF). Requirementsformaintenance(MEm), includingmajorcomponentsof FHPandphysical activity, areestablished at around 155 kcal kg BW0.60. We recently reported that maintenance requirements for young broilers based onkg BW0.75were 8% lower than the values estimated using kg BW0.60, and that BW raised to the exponent 0.60, was a morepreciseestimator.Grossenergyretainedinthebodyasfat(TERF)andprotein(TERP),togethercontributemostofthetotal energy retained (TER) in the body. Efficiency of ME utilization above maintenance varies from 70 to 84% for lipiddepositioninadultbirdsandbetween37and85%ingrowingbirds.Keywords: Energy,broiler,metabolicrate,energyretentionLopez, G. etLeeson, S. 2008. Re partitiondele nergiechezlepouletdechair. Can. J. Anim. Sci. 88: 205212. Le nergieme tabolisable (EM) est le talon habituellement employe en nutrition, tant dans le commerce quen recherche, pour de crirelesbesoinsde nergiedelavolailleetle nergiecontenuedanslesaliments.Le nergiedesalimentsexerceuneinfluencesurlingestiondesautrese le mentsnutritifs. Lespouletsdechairmontrentunecapacite e tonnanteenmodifiantlaquantitedaliment inge re e en fonction de la concentration de nergie dans la ration. Lexactitude, la pre cision et lutilite des diversesme thodes servant a` de terminer laquantite deEMdans larationet ses composantes font toujours lobjet dunevivepole mique.Enge ne ral,onre partitlaEMinge re eenplusieurse le ments,a` savoirle nergieretenue(ER)danslestissusdelorganisme(principalement sousformedematie` regrasseet deprote ines) et cellelibe re esousformedechaleur(CH),EMCHER.Onarelativementpeuestime laCHetsescomposantes,soitlachaleurproduitedurantlejeu ne(CHJ),cellere sultantdelactivite physiqueet leffetthermiquedu a` lalimentation(ETA).On fixelesbesoinsdentretien (EMe),qui incluent la CHJ et lactivite physique, autour de 155 kcal par kg de poids corporel (PC) multiplie par lexposant 0,60.Les auteurs ont re cemment signale que les besoins dentretien des jeunes poulets calcule s en fonction du PC0,75sont de 8%infe rieursaux valeursestime es parkg dePC0,60, et que le PC multiplie parlexposant0,60 en permetune estimationpluspre cise. Le nergie brute conserve e dans le corps sous forme de matie` re grasse et de prote ines explique la majeure partie dele nergie totale garde e par lorganisme. Au-dessus des niveaux dentretien, lefficacite dutilisation de la EM varie entre 70et84%pourlede po tdeslipideschezlesoiseauxadultesetentre37et85%chezceuxencroissance.Motscle s: Energie,pouletdechair,vitessedeme tabolisme,re tentiondele nergieThe energycontributionfrompoultrydiets is usuallydescribed in terms of metabolizable energy (ME) and/ornet energy(NE). Incommercial nutritionandinmostresearchstudies,MEisthestandardmeasureofenergyusedindescribingbothenergyrequirementsanddietsforpoultry.MEcanbeaccuratelydeterminedfromthedifferencebetweenthegrossenergyofthefeedandthegross energy of the excreta derived fromsuch feed[National Research Council (NRC) 1994]. ME has beencommonly acceptedandextensively usedtocompareenergyvalues of feedstuffs, anddiets for poultry, andenergyrequirements are commonlyexpressedintheseunits.However,MEisrarelymeasuredundercommer-cialconditions.1Towhomcorrespondenceshouldbeaddressed(e-mail:sleeson@uoguelph.ca).Abbreviations: BW, body weight; E:P, energy:protein; ER, energyretained; ERF, energyretainedinthebodyasfat;ERP,energyretainedinthebodyasprotein; FHP, fastingheat production; HP, heatproduction; ME, metabolizable energy; MEm, MEintake for maintenance; MEI, ME intake; TEF,thermic effect of feeding; TER, total energyretained; TERF, total energy retainedinthe bodyas fat; TERP, total energyretainedinthebodyasprotein205Theconcentrationof energyinthediet will greatlyinfluence the intake of all other nutrients andsotheutilization of MEand these other nutrients. In thisregard, broilers exhibit the ability to control energyintake by adjusting their feed intake as diet energyconcentrationchanges(Leesonetal.1996a,b).MEisanexpensivecomponent of poultrydietsandrepresents alarge portionof the total cost of broilerproduction.Manyattemptshavebeenmadetoincreasethe accuracy, precision and speed of methods ofdetermining ME values, and especially for dietaryingredients(Sibbald1976,1979;Farrell1978;DaleandFuller1984;McNabandBlair1988).Thissituationhasbeen especially critical in the broiler industry, sincebroilersconsumelargeamountsoffeedcomparedwithotherpoultryspecies,andtherearedifficultiesinherentin working with young birds in various bioassays(LeesonandSummers2005).There is still considerable debate on the accuracy,precision and usefulness of different procedures de-scribedintheliteraturefordeterminingMEvalues ofdiets and ingredients. Some of the factors that influenceME values have been the variability of ME values acrosslaboratories andthe different methods usedfor mea-surement (Bourdillonat al. 1990a), andespeciallythelackofagreementonthesuitabilityoftheadultroostertodetermine MEvalues for growingbroilers. Differ-ences in ME values have been reported when comparingyoung broilers and adult roosters (Kussaibati et al.1982;Mollahetal.1983;Ha rtel1986;Bourdillonetal.1990b; Carre etal. 1995; Farrell etal. 1997)andadultlayinghens(Petersenetal.1976;Farrelletal.1997).Another factor influencingMEvalues has beenthepractice of adjusting ME values for nitrogen (N)retention(MEn). Thisisacommonpracticeinpoultrynutrition, andMEnvalues of different ingredientsarecommonlyreportedintheliterature(NRC1994). It isgenerally accepted that correction to zero N retention isessential when comparing ME values across species thathave inherently different rates of growth or egg produc-tion, andhence different levels of nitrogenretention.Likewise, Ncorrectionseemsessential forcomparisonof theMEvalues determinedwithjuvenilevs. maturebirds, since the former will be gaining body protein,whilethelatter areusuallyat zeronitrogenretention.Some 50 yr since the first application of correctionfornitrogenbalancebyHill andAnderson(1958), thecorrectionfactorisstilldebated, especiallyforgrowingbroilers, where dietary protein is penalized assumingthat none of it is deposited as protein tissue (De Groote1974; Sibbald1982; McNab2000; Lopez andLeeson2007,2008).Energysystems, includingthat for ME, areusedtopredict values of feeds relativetoenergyrequirementsformaintenanceandproduction.Thisscenarioisbasedontheconcept of partitioningenergyrequirements ofgrowing animals betweenrequirementsfor maintenanceandproduction(Birkett andDe Lange 2001a; Lopezand Leeson 2007). Currently, factorial models arecommonlyusedtorepresent the relationshipbetweenMEintake(MEI) andenergyretained(ER), includingrequirements for maintenance (MEm) (Kielanowski1965; Birkett andDeLange2001a; LopezandLeeson2007). In this model, the utilization of ME intake abovemaintenance depends on the partition of energy retainedasprotein(ERP)andasfat(ERF)andtheirrespectiveefficiencies for deposition. There is current interest inbroiler research, inquantifyingandpartitioningdailyER in the body, as ERF and ERP, and the utilization ofMEintake(VanMilgenetal. 2001;LopezandLeeson2005).As broilers grow, accretion of body fat and bodyprotein is impacted by nutrition, bird strain, sex,environmentalconditions,bodyweight(BW)andasso-ciated degree of maturity, and by the interactionbetween some or all these parameters. Diet compositioncan have a major impact on carcass compositionthroughthe depositionof nutrients as fat or protein.To quantify these body components during growth and/or over time, several mathematical models have beendeveloped (Wilson 1977; Wiseman and Lewis 1998).Genetic improvements ingrowthrate have beenpro-gressiveandgenerallyaheadoftheestablishednutrientrequirements, leaving most recommendations quicklyredundant(NRC1994). Thisselectionforbodyweightgainhas resultedinbroilers that reachmarket weightearlier (Nicholson 1998; Remignon and Le Bihan-Duval2003) at animmaturebodyweightand oftenwithoutachieving maximum genetic potential for fat and proteindeposition in terms of absolute quantities depositedeach day. Understanding the energy requirements of thebirds andhowmodernbroilers quantitativelydepositfatandproteinduringacommerciallifecyclewouldbeusefulto the industry so as to establish usefuleconomicmodelsthattakeintoaccountthebiologyofgrowthofbroilerchickens.IMPACTOFBODYCOMPOSITIONONENERGYREQUIREMENTSAfter hatching it is expected that as body weightincreases over time, thequantities andproportions ofbody fat and protein increase at different rates (Emmans1995) withfat deposits potentiallyincreasingfaster atolder ages (Leenstra 1986). The relationshipbetweenproteinandfat inthebodyis influencedbynutrition(DeschepperanddeGroote1995; WisemanandLewis1998),genotype(EdwardsandDenman1975; Leenstra1988, 1989; Havenstein et al. 1994 a, b), sex (Leeson andSummers 1980; Cahaner andLeenstra1992; LeenstraandCahaner1992),environmentalconditions(Kubenaet al. 1972; CahanerandLeenstra1992; LeenstraandCahaner1992), andbodyweight (BW) andassociateddegree of maturity (Leenstra 1986, 1989; Havensteinetal.1994a;Decuypereetal.2003).Carcassfatisgenerallyconsideredtobeanunfavor-able trait in the broiler industry (Remignon and Le206 CANADIANJOURNALOFANIMALSCIENCEBihan-Duval 2003), leadingtostudiesingeneticselec-tion (Whitehead and Griffin 1984; Leenstra 1988,Whitehead 1990; Pym et al. 2004) and nutrition (ZubairandLeeson1994; LeesonandZubair 1997) aimedatreducing or limiting carcass fat. Inmost commercialfeeding programs, the desire for fast growthwithadlibitumfeeding invariably entails moderate levels ofenergyandhighcrudeproteinforthestarterdiets,andhighenergyandlowercrudeproteinforthelaterdiets(Leeson and Summers 2005). It is well documentedthat such changes to energy:protein (E:P) in the diet areassociated with increased weight gain as fat (Bartovet al. 1974; MacLeod1990, 1991; WisemanandLewis1998;Morris2004).LeesonandSummers(1980) investigatedbodycom-ponentsinmaleandfemalebroilersto70dinresponseto increasing energy:protein (E:P) in the diet. Theseauthors reportedthat as BWincreases, bothfat andproteindepositionincrease, withbodyfatcontentasapercent of the body weight increasing most dramaticallyinbothmalesandfemales, whilebodyproteincontentremainedfairlyconstant. SuchincreasesincarcassfatdepositionareconfoundedbytheusualincreaseinE:Pinthedietasthebirdages(WisemanandLewis1998)andthedesiretoachievegeneticpotential for growth(Havensteinet al. 1994a, b). Proteinaccretion, ontheother hand, is usually predetermined by the geneticpotential of the bird, assumingthe diet supplies ade-quate amounts and balance of amino acids. Leaner birdsusually result fromusing a single experimental dietwhere protein/AA and energy are constant (Leeson et al.1996a, b). Selection for reduced abdominal fat (Cahaner1988; Leclercq 1988) and improved feed efficiency(Leenstra1988; Buyseetal. 1998)hasproducedleanerbroilers, although, again, this will be affectedbydietenergylevelusedinagivenstudy.Mathematical growth models have been used to studytheinfluenceofchangeovertimeindietenergy(Wise-manandLewis 1998), or dietary protein(Eits et al.2005) onbodycomponents suchasfat (WisemanandLewis1998).ThesemodelsareusedasatooltopredictBWwithdesiredcarcasscharacteristics.TheGompertzequationhas alsobeenadoptedinbroiler studies toappropriatelydescribegrowthovertime(Wilson1977;Emmans 1995; Hurwitz and Talpaz 1997; Darmani et al.2002) and/or growthof body components inbroilers(Tzeng and Becker 1981; Peter et al. 1997; Wiseman andLewis 1998; Gous et al. 1999). This equation describes asigmoidal patternwithslowinitial growthfollowedbyaccelerationuptoacertainage (the inflectionpoint)followedby subsequent decrease inthe rate as bodyweight approaches its maximum near to sexual maturity(Hurwitz andTalpaz 1997). TzengandBecker (1981)fittedthe nonlinear Gompertz equationtoabdominalfat, intending to predict total carcass fat over time(Becker et al. 1979). Usually the methods for evaluatingthegrowthofbodycomponentsinbroilerstudiesusingthe Gompertz model have been carried out for extendedperiodsof timeupto10to16wk(TzengandBecker1981;Peteretal.1997;WisemanandLewis1998;Gouset al. 1999). Under these conditions, the asymptoticvaluesofliveweightorbodycomponentsareobviouslybetter estimated. However, as todays broilers reachcommercial bodyweight earlier (approximately6wk)without achieving maximumgenetic potential for fatandproteindeposition, the asymptotic value of live-weightorbodycomponentswill neverberealized, andthis may leadtopotentially unreliable predictions ofbody weight, fat or protein deposition using such modelpredictions(LopezandLeeson2007).PARTITIONINGOFMETABOLIZABLEENERGYMEintakeisgenerallypartitionedintoenergyretained(ER)inbodytissues(mainlyasfatandprotein)andasheat production (HP): MEHPER (Close 1990;Lawrence andFowler 2002). Inthermoneutral condi-tions,HPrepresentsheatassociatedwiththeutilizationof MEintakeformaintenance(MEm) andproductiveprocesses, which, in juvenile broilers, represents 5264%of intake (Fuller et al. 1983; VanMilgenet al. 2001;Noblet et al. 2003). Therefore, ER represents thedifferencebetweenMEandHPandsoMEHPER.WhenevaluatingER, itisnecessarytomeasureenergyretainedas bothfat (ERF) andprotein(ERP), alongwith their efficiency of utilization of ME, usually termedkf for fat and kp for protein deposition. Estimatesof ERFand ERP in broilers have been determinedusing such methods as indirect calorimetry (Farrell1974;Fulleretal.1983;VanMilgenetal.2001;Nobletet al. 2003) and comparative slaughter (Fuller et al.1983; MacLeod1991). However, values forkf andkphaveonlybeenestimatedusingstatistical modelsfromexperiments involving varying degrees of quantitativefeedrestriction.(Boekholtetal.1994).There have been limitations in nutritional studiesusinggrowingbroilerstoadequatelydefineMEutiliza-tion and, consequently, their energy requirements. Therearefewreportedestimatesof HPanditscomponents,fastingheatproduction(FHP), heatproductionduetophysical activity and the thermic effect of feeding (TEF)(VanMilgenet al. 2001; Noblet et al. 2003). Feedingbroilers from 21 to 35 d of age, Van Milgen et al. (2001)subdividedHPintoits threemajor components usingindirect calorimetry, showing that FHPand physicalactivitytogether represents 3637%of MEintake. Intheir experiment, Van Milgen et al. (2001) describedphysicalactivityasamajorcomponentofmaintenance(810%). Requirements for MEm, including majorcomponentsof FHPandphysical activity, wereestab-lishedat 152157 kcal kg BW0.60. These values weresimilar (155 kcal kg BW0.60) to those reported by Lopezand Leeson (2005) using comparative slaughter, and thesameestimateofmetabolicbodymodifier(kgBW0.60).There are few estimates of the efficiency of MEutilization for fat and protein deposition. In mostpublished studies, estimates for kf and kp are establishedLOPEZANDLEESON *ENERGYPARTITIONINGINBROILERCHICKENS 207through experiments involving the feeding of gradedlevelsofenergyorwithawiderangeofinducedenergyintakes soas toobtaindifferent rates of proteinandlipiddeposition(Boekholt et al. 1994). This approachhas beenquestionedinstudies withgrowingpigs, theargument beingthat inmost animals fat andproteindepositionare confounded(Noblet et al. 1999). Cur-rently, the model that is most commonly used to predictthe effect of diet on growth (ERF and ERP) andefficiency is based on the equation of Kielanowski(1965).Inthismodel,MEintake(MEI)isdefinedas:MEIMEm(1=kf ERF)(1=kpERP)where MEmMEfor maintenance as a function ofbody weight (BWb), and kf and kpefficiencies ofutilization of ME for fat and protein deposition,respectively(Boekholtetal.1994;BirkettanddeLange2001a;LawrenceandFowler2002).MAINTENANCEENERGYREQUIREMENTSMaintenance energy requirement is described as thestateoftheanimalwhereitsbodycompositionremainsconstant and when there is no production or work/activity(LarbierandLeclercq1994; Wenketal. 2001).Therearefewestimatesofmaintenanceenergyrequire-ments in poultry (MacLeod et al. 1988; Sakomura et al.2003)and, inparticular, growingbroilers(VanMilgenetal.2001;LopezandLeeson2005).MEmrepresents a large portion of the MEI inbroilers, being in the order of 4244%(Lopez andLeeson2005), andisinfluencedbythemethodusedtoexpress MEm. The MEmof broilers is traditionallyreportedasafunctionofBWraisedtothe0.75power(Fuller et al. 1983; MacLeod 1990; Boekholt et al. 1994;Buyse et al. 1998). Recent information suggests thatMEminbroilersis, infact, moreadequatelydescribedby BW exponents other than 0.75 (MacLeod 1991, 1997;VanMilgenetal. 2001; Nobletetal. 2003; LopezandLeeson 2005). This difference directly influences thepartitioning of energy between maintenance, fat andprotein deposition and, by inference, efficiency of energyuse. Underestimationof MEmfor younger or smallerbirdsimplieslessenergyforproductionandtherefore,bycalculation, greater apparent efficiencyfor growth(higher kpandkf). Theconverse effect, but toalessdegreeis expectedforoverestimationof MEmforolderheavier birds (Lopez and Leeson 2005). Fewstudieshave been conducted in order to comprehensivelyunderstand the efficiencies for protein and fat depositioninpoultry, andmost suchdataare basedonBW0.75(Boekholt et al. 1994), or data extrapolated from studieswithpigs (Birkett andde Lange 2001b; Noblet et al.1999). Lopez andLeeson(2005) reportedthat main-tenance requirements for youngbroilers basedonkgBW0.75were8%lowerthanthevaluesestimatedusingBW0.60, and that BW raised to the exponent 0.60, was amore precise estimator. Close (1990) indicated thatdifferencesinMEmaremainlyaffectedbychangesinbodycomposition. Since, at agivenbodyweight, fattissue contributes little to heat production comparedwiththat of muscle, it is suggestedthat maintenanceenergyrequirements are lower infat animals thaninleananimals(Close1990). MacLeodet al.(1988)foundsignificantly higher fasting heat production and Nretention in broiler lines selected for leanness than thoseselected for fatness, suggesting an increased mainte-nanceenergyrequirement inleanbirds. Questionsstillremain whether fat animals have lower MEmor ifanimalswithalowerMEmbecomefatter(VanMilgenetal.1998).RETAINEDENERGYASFATANDPROTEINANDEFFICIENCYOFENERGYRETENTIONAs broilers grow, accretionof fat andproteinis theresult of the interaction among bird strain, sex, environ-mental conditions, nutrition, body weight (BW) anddegreeof maturity. It isexpectedthat matureanimalsretain energy mainly as fat, while growing animals retainenergy as both fat and protein. Gross energy retained inthebodyasfat (TERF) andprotein(TERP), togethercontributemost of thetotal energyretained(TER) inthebody. TERiscalculatedfromaccumulationof fatandproteinandbyusingcorrespondingenergyvaluesof 9.5 kcal g1fat and 5.7 kcal g1of protein(Znaniecka 1967; Hakansson and Svensson 1984). Sincefat and protein accretion likely differ in their efficienciesof transfer of energyfromfeedtotissue(ButteryandBoorman1976; Pullar andWebster 1977), changes intheproportionof bothfat andproteinduringgrowthinfluence the total energy in the body and especially theefficiencyofsuchgain.Variousstudieshaveindicatedthat theefficiencyofproteindepositionislowerthanthatforfatdeposition(Petersen1970;DeGroote1974; Boekholtetal. 1994).De Groote (1974) reportedthat the efficiencyof MEutilization above maintenance for lipid deposition inadultbirdsvariesfrom70to84%andbetween37and85%in growing birds. Petersen (1970), using WhitePlymouth Rockbirds,estimated efficiencies of 0.51 and0.78forproteinandfat, respectively, indicatinganeedfor11.2kcal ofMEg1proteinand12.2kcal ofMEg1of fat deposited. More recent information ingrowing broilers suggests higher energetic efficienciesfor protein (0.66) and fat (0.86) deposition, (Boekholt etal. 1994), indicatinglowerneedsforprotein(8.63kcalMEg1) andfat deposition(10.9kcal of MEg1).Similar efficiencies (0.65 and 0.83) are reported incomparable studies with growing pigs (Noblet et al.1999). Moreover, duetothecloseassociationbetweenbody water and body proteininlean meat, the MErequirements per gramof lean tissue gain are muchlower than those per unit of fat tissue gain. BothincreasesinERP/ERFandreductionsinenergyneedsper gramof protein depositioncontribute to increase in208 CANADIANJOURNALOFANIMALSCIENCEfeedefficiencyinmodernbroilers (Lopezet al. 2007).Broilersmayalsohavebeeninadvertentlyselectedforgreaterrateofproteinsynthesisand/orreducedproteindegradation(UrdanetaandLeeson2004).Variationinkpandkf (Petersen1970; De Groote1974;Boekholtetal.1994)isduetosuchfactorsasthenatureof thediet, animal effectsandthefunctionforwhichfeedisusedbytheanimal(BirkettanddeLange2001a).Forexample,studiesingrowingpigsshowthatMEfromdietary fat is used very efficiently for fatdeposition (0.90), while lower values are reported for theformationoffatfromprotein(0.66).Thisisduetothedifferent energeticefficienciesinthechemical transfor-mations involved in the synthesis of fat and protein fromabsorbednutrients(VanMilgenetal.2001).Metabolizable energyintake is well documentedtoinfluencebodycomposition(HakanssonandSvensson1984; Boekholt et al. 1994; WisemanandLewis1998)and therefore body TER. Boekholt et al. (1994) fedbroilersfrom 60 to 100% of normaldaily energyintakeand reported thatdaily retention of fat and protein waslinearlyrelatedtoenergyretentionsuggestingthat ingrowingbroilerseachadditionalunitofgaingeneratedby energyintake over 43 kcalkg W0.75d was composedof constant amounts of proteinandfat, but differentproportionsofenergyasprotein(15%)andfat(85%).These datasuggest thatat an ER of 43kcalkg W0.75d,ERF is zero and only protein is retained, perhaps at theexpenseoffatmobilization(Boekholtetal.1994).CONCLUSIONSToday, broilers reach commercial body weight veryearly, at an immaturebody weight and often withoutachieving maximum genetic potential for fat and proteindeposition in terms of absolute quantities depositedeachday. It is calculatedthat withinthe commercialgrowingrangeof042d, broilersdepositbodyfatandprotein that together represent 35 to 40%of theirdailyMEintake(LopezandLeeson2005).QuantifyingandpartitioningTERas TERFandTERPas majorcomponents of the requirement of ME in growingbroilerscanbeusedintheindustrytoestablishusefulmodelsthatwill haveeconomicconsequencesallowingbetter management decisions andtakingintoaccountthe biological need of growth of modern birds within thejuvenilecommercialagerange.Anderson, D. L., Hill, F. W. and R. R. 1958. Studies ofmetabolizable and productive energy of glucose for thegrowingchick.J.Nutr.65:561574.Bartov, I., Bornstein, S. and Lipstein, B. 1974. Effects of calorietoproteinratioonthe degree of fatness inbroilers fedonpracticaldiets.Br.Poult.Sci.15:107117.Becker,W. A., Spencer, J. V., Mirosh, L. W. and Verstrate,J.A. 1979. Predictionof fat andfat freeliveweight inbroilerchickens using backskin fat, abdominal fat and live bodyweight.Poult.Sci.58:835842.Birkett, S. andDeLange, K. 2001a. Limitations of conven-tional modelsand a conceptualframework fora nutrient owrepresentation of energy utilization by animals. Br. J. Nutr. 86:647659.Birkett, S.andDeLange,K.2001b.Calibrationofanutrientowmodelofenergyutilizationbygrowingpigs.Br.J.Nutr.86:675689.Boekholt, H. A., Van der Grinten, P. H., Schreurs, V. V. A. M.,Los, M. J. N. and Leffering, C. P. 1994. Effect of dietaryenergyrestrictionsonretentionof protein, fatandenergyinbroilerchickens.Br.Poult.Sci.35:603614.Bourdillon, A., Carre , B., Conan, L., Duperray, J., Huyghe-baert, G., Leclercq, B., Lessire, M., McNab, J. and Wiseman, J.1990a.Europeanreferencemethodfortheinvivodetermina-tionofmetabolisableenergywithadultcockerels: reproduci-bility, effect of foodintakeandcomparisonwithindividuallaboratorymethods.Br.Poult.Sci.31:557565.Bourdillon, A., Carre , B., Conan, L., Francesch, M., Fuentes,M., Huyghebaert, G., Janssen, W. M. M. A., Leclercq, B.,Lessire, M., McNabJ., Rigoni, M. andWiseman, J. 1990b.European reference method of in vivo determination ofmetabolisable energy in poultry: reproducibility, effect ofage, comparison with predicted values. Br. Poul. Sci. 31:567576.Buttery, P. J. and Boorman, K. N. 1976. The energeticefciencyof aminoacidmetabolism. Pages197206inD. J.A.Cole,K.N.Boorman,P.J.Buttery,D.Lewis,R.J.Neal,andH. Swan, eds. Proteinmetabolismandnutrition. Butter-worths,London,UK.Buyse, J., Michels, H., Vloeberghs, J., Saevels, P., Aerts, J. M.,Ducro, B., Berckmans, D. and Decuypere, E. 1998. Energy andprotein metabolism between 3 and 6 weeks of age male broilerchicken selected for growth rate or for improved foodefciency.Br.Poult.Sci.39:264272.Cahaner, A. 1988. Experimental divergent selection on abdom-inal fat inbroilers female andmale type lines andtheircrosses. Pages7186inB. LeclercqandC.C. Whiteheadeds.Leannessindomesticbirds: genetic, metabolicandhormonalaspects.Butterworths,London,UK.Cahaner, A. and Leenstra, F. 1992. Effects of high temperatureon growth and efciency of male and female broilers from linesselectedforhighweightgain,favourablefeedconversion,andhighorlowfatcontent.Poult.Sci.71:12371250.Carre , B., Gomez, J. and Chagneau, A. M. 1995. Contributionof oligosaccharideandpolysaccharidedigestion, andexcretalosses of lactic acidandshort chainfatty acids, todietarymetabolisable energy values in broiler chickens and adultcockerels.Br.Poult.Sci.36:611629.Close, W. H. 1990. The evaluationof feeds throughcalori-metrystudies. Pages2139inJ. WisemanandD. J. A. Coleeds. Feedstuff evaluation. Butterworths, The University Press,Cambridge,UK.Dale, N. and Fuller, H. L. 1984. Correlation of protein contentof feedstuffs with the magnitude of nitrogen correction in truemetabolizable energy determinations. Poult. Sci. 63: 10081012.Darmani, K. H., Kebreab, E., Lopez, S. and France, J. 2002. AderivationandevaluationofthevonBertalanffyequationfordescribing growth in broilers over time. J. Anim. Feed Sci. 11:109125.Decuypere, E., Bruggeman, V., Barbato, G. F. andBuyse, J.2003. Growth and reproduction problems associated withselectionforincreasedbroilermeat production. Pages1328in W. M. Muir and S. E. Aggrey, eds. Poultry genetics,breedingandbiotechnology.CABIPublishing,Oxford,UK.LOPEZANDLEESON *ENERGYPARTITIONINGINBROILERCHICKENS 209De Groote, G. 1974. Utilisation of metabolisable energy. Pages113133inEnergyrequirementsofpoultry.T.R.MorrisandB.M.Freeman,eds.BritishPoultryScienceLtd.,Edinburgh,UK.Deschepper, K. and De Groote, G. 1995. Effect of dietaryprotein, essential and non-essential amino acids on theperformance and carcase composition of male broiler chickens.Br.Poult.Sci.36:229245.Edwards, H. M., Jr. andDenman, F. 1975. Carcasscomposi-tion studies. 2. Inuence of breed, sex and diet on grosscompositionofthecarcassandfattyacidcompositionoftheadiposetissue.Poult.Sci.54:12301238.Eits, R. M., Kwakkel, R. P., Verstengen, M. W. A. andDenHartog, L. A. 2005. Dietary balanced protein in broilerchickens. 1. Aexible and practical tool to predict dose-responsecurves.Br.Poult.Sci.46:300309.Emmans, G.C. 1994. Effective energy: a concept of energyutilizationappliedacrossspecies.Br.J.Nutr.71:801821.Emmans, G. C. 1995. Problems inmodellingthe growthofpoultry.WorldsPoult.Sci.51:7789.Farrell, D. J. 1974. General principles andassumptions ofcalorimetry. Pages124inT. R. MorrisandB. M. Freeman,eds. Energyrequirements of poultry. BritishPoultryScienceLtd.,Edinburgh,UK.Farrell, D. J. 1978. Rapid determination of metabolisableenergyoffoodsusingcockerels.Br.Poult.Sci.19:303308.Farrell, D. J., Smulders, A., Mannion, P. F., Smith, M. andPriest, J. 1997. The effective energy of six poultry dietsmeasuredinyoungandadult birds. Pages 371374inK. J.McCraken, E. F. Unsworth, and A. R. G. Wylie, eds.Proceedingof the 14thSymposiumonEnergyMetabolism.Newcastle, Co. Down, NorthernIreland. CABInternational,Oxford,UK.Fuller,H.L.,Dale,N.M.andSmith,C.F.1983.Comparisonof heat productionof chickens measuredbyenergybalanceandbygaseousexchange.J.Nutr.113:14031408.Gous, R. M., Moran, E. T., Jr., Stilborn, H. R., Bradford, G. D.and Emmans, G. C. 1999. Evaluation of the parameters neededtodescribetheoverall growth, thechemical growth, andthegrowth of feathers and breast muscle of broilers. Poult. Sci. 78:812821.Hakansson,J. and Svensson,S. A.1984. Gross energycontentof fat andproteinindifferent tissuesof malebroilerchicks.Swed.J.Agric.Res.14:207212.Ha rtel, H. 1986. Inuence of foodinput andprocedure ofdeterminationonmetabolisableenergyanddigestibilityof adietmeasuredwithyoungandadultbirds. Br. PoultSci. 27:1139..Havenstein,G.B.,Ferket,P.R.,Scheideler,S.E.andLarson,B. T. 1994a. Growth, livability, and feed conversion of 1991 vs1957broilerswhenfedtypical 1957and1991broilerdiets.Poult.Sci.73:17851794.Havenstein, G. B., Ferket, P. R., Scheideler, S. E. and Rives, D.V. 1994b. Carcass composition and yield of 1991 vs 1957broilerswhenfedtypical1957and1991broilerdiets.Poul.Sci.73:17951804.Hill, F. W. and Anderson, D. L. 1958. Comparison ofmetabolizable energy andproductive energy determinationswithgrowingchicks.J.Nutr.64:587603.Hurwitz, S. andTalpaz, H. 1997. Modellingofgrowth. Pages148157in11thEuropeanSymposiumonPoultryNutrition.Faaborg,Denmark.Kielanowski, J. 1965. Estimatesoftheenergycostofproteindeposition in growing animals. Pages 1320 in K.L. Blaxter ed.Proceedings of the 3rdSymposiumonEnergyMetabolism.EAAPPubl.no.11.AcademicPress,London,UK.Kubena,F., Lott,B. D.,Deaton,J.W., Reece,F.N.and May,J. D. 1972. Body composition of chicks as inuenced byenvironmental temperature and selected dietary factors. Poult.Sci.51:517522.Kussaibati, R., Guillaume, J. and Leclercq, B. 1982. The effectsof age, dietary fat, bile salts, and feeding rate on apparent andtrue metabolisable energy values in chickens. Br. Poult. Sci. 23:393403.Larbier, M. and Leclercq, B. 1994. Energy metabolismin nutrition and feeding of poultry. M. Larbier and B.Leclercq, eds. NottinghamUniversityPress. Loughborough,UK.pp4773.Lawrence, T. L. L. andFowler, V. R. 2002. Efciencyandgrowth. Pages 216228 in T. L. J. Lawrence and V. R. Fowler,eds. Growthof farmanimals. CABIPublishing, NewYork,NY.Leclercq,B.1988.Geneticselectionofmeat-typechickensforhigh or low abdominal fat content. Pages 2540 in B. Leclercqand C. C. Whitehead, eds. Leanness in domestic birds:Genetic, metabolic and hormonal aspects. Butterworths,London,UK.Leenstra, F. R. 1986. Effect of age, sex, genotype andenvironmentonfatdepositioninbroilerschickens.Br.Poult.Sci.42:1225.Leenstra, F. R. 1988. Selection for leaness: results of theSpelderholtexperiment. Pages5970inB. LeclercqandC. C.Whitehead, eds. Leanness indomestic birds: Genetic, meta-bolicandhormonalaspect.Butterworths,London,UK.Leenstra, F. R. 1989. Inuence of diet and genotype on carcassquality in poultry, and their consequences for selection.Pages131144inD.J. A.ColeandW. Haresigneds.Recentdevelopmentsinpoultrynutrition.Butterworths,Essex,UK.Leenstra,F.R.andCahaner,A.1992.Effectsoflowandhightemperaturesonslaughteryieldofbroilersfromlinesselectedforhighweightgain,favourablefeedconversion,andhighorlowfatcontent.Poult.Sci.71:19942006.Leeson, S., Caston, L. and Summers, J. D. 1996a. Broilerresponse toenergyandproteindilutioninthe nisher diet.Poult.Sci.75:522528.Leeson, S., Caston, L. and Summers, J. D. 1996b. Broilerresponsetodietenergy.Poult.Sci.75:529535.Leeson, S. andSummers, J. D. 1980. Productionandcarcasscharacteristicsofthebroilerchicken.Poult.Sci.59:786798.Leeson, S. andSummers, J. D. 2005. Feedingprograms forbroilers chickens. Pages 229296 in S. Leeson and J. D.Summerseds. Commercial poultrynutrition. 3rded. Univer-sityBooks,Guelph,ON.Leeson, S. andZubair, A. K. 1997. Nutritionof the broilerchicken around the period of compensatory growth. Poult. Sci.76:992999.Lopez, G. andLeeson, S. 2005. Utilizationof metabolizableenergybyyoungbroilers andbirds of intermediate growthrate.Poult.Sci.84:10691076.Lopez, G. andLeeson, S.2007. Relevanceofnitrogencorrec-tionfor assessment of metabolizableenergywithbroilers toforty-ninedaysofage.Poult.Sci.86:16961704.Lopez, G. andLeeson, S. 2008. Assessment of the nitrogencorrectionfactor inevaluatingmetabolizableenergyof cornand soybean meal in diets for broilers. Poult. Sci. 87: 298306.210 CANADIANJOURNALOFANIMALSCIENCELopez, G., deLange, K. andLeeson, S. 2007. Partitioningofretained energy in broilers and birds with intermediate growthrate.Poult.Sci.86:21622171.MacLeod, M. G. 1990. Energyandnitrogenintake, expendi-tureandretentionat 208ingrowingfowl givendietswithawiderangeof energyandproteincontents. Br. J. Nutr. 64:625637.MacLeod,M.G.1991.Fatdepositionandheatproductionasresponse to surplus dietary energyin fowls given a wide rangeof metabolizable energy: protein ratios. Br. Poult. Sci. 32:10971108.MacLeod, M. G. 1997. Effects of aminoacid balance andenergy: proteinratioonenergyandnitrogenmetabolisminmalebroilerchickens.Br.Poult.Sci.38:405411.MacLeod, M. G. 2002. Energyutilization: measurement andprediction.Pages191217inJ.M.McNabandK.Boorman,eds. Poultry feedstuffs supply, composition and nutritivevalue.CABIPublishing,Oxford,UK.MacLeod,M.G.,Whitehead,C.C.,Grifn,H.D.andJewitt,T. R.1988. Energyandnitrogenretentionandlossinbroilerchickens genetically selected for leanness and fatness. Br.Poult.Sci.29:285292.McNab, J. M. 2000. Rapid metabolizable energy assays. Pages307315 in J. P. F. D?Mello, ed. Farm animal metabolism andnutrition.CABIPublishing,Oxford,UK.McNab, J. M. andBlair, J. C. 1988. Modiedassayfortrueandapparent metabolisableenergybased ontubefeeding.Br.Poult.Sci.29:697707.Mollah, Y., Bryden, W. L., Wallis, I. R., Balnave, D. andAnnison, E. F. 1983. Studies on lowmetabolisable energywheats for poultry using conventional and rapid assayprocedures andtheeffects of processing. Br. Poult. Sci. 24:8189.Morris, T. R. 2004. Nutritionof chicks andlayers. WorldsPoult.Sci.60:518.National Research Council. 1994. Nutrient requirements ofpoultry. 9threv. ed. National AcademyPress, Washington,DC.Nicholson, D. 1998. Research: is it the broiler industryspartner into the newmillennium? Worlds Poult. Sci. 54:271278.Noblet, J., Karage, C., Dubois, S. and Milgen, J. 1999.Metabolic utilization of energy and maintenance requirementsingrowingpigs: effects of sexandgenotype. Anim. Sci. 77:12081216.Noblet, J., VanMilgen, J., Carre , B., Dimon, P., Dubois, S.,Rademacher, M. andVanCauwenberghe, S. 2003. Effect ofbody weight and dietary crude protein on energy utilization ingrowingpigsandbroilers. Pages205208inW. B. SouffrantandC. C. Metges, eds. Progress inresearchonenergyandproteinmetabolism. EAAPPubl. no109. WageningenAca-demicPublishers,Wageningen,theNetherlands.Peter, W., Danicke, S. andJeroch, H. 1997. DescriptionofgrowthofbodyweightandbodyproteinofFrenchlabeltypechickens with Gompertz equations is dependent on the proteincontentofthediet. Pages400402in11thEuropeanSympo-siumonPoultryNutrition.Faaborg,Denmark.Petersen, C. B. 1970. Efciency of protein and fat deposition ingrowing chickens determined by respiration experiments.Pages205208inA. Schu rchandC. Wenk, eds. Proceedingof the 5th EAAPSymposiumon Energy Metabolismof FarmAnimals.Zurich,Switzerland.Petersen, C. F., Meyer, G. B. and Sauter, E. A. 1976.Comparison of metabolizable energy values of feed ingredientsforchicksandhens.Poult.Sci.55:11631176.Pullar, J. D. and Webster, A. J. F. 1977. The energy cost of fatandproteindepositionintherat.Br.J.Nutr.37:355363.Pym, R. A. E., Leclercq, B., Tomas, F. M. andTesseraud, S.2004. Protein utilization and turnover in lines of chickensselectedfordifferentaspectsofbodycomposition. Br. Poult.Sci.45:775786.Remignon, H. and Le Bihan-Duval, E. 2003. Meat qualityproblems associatedwithselectionfor increasedproduction.Pages 5366inW. M. Muir andS. E. Aggrey, eds. Poultrygenetics, breeding and biotechnology. CABI Publishing,Oxford,UK.Sakomura, N. K., Silva, R., Couto, H. P., Coon, C. andPacheco, C. R. 2003. Modellingmetabolizableenergyutiliza-tioninbroilerbreederpullets.Poult.Sci.82:419427.Sibbald, I. R. 1976. A bioassay for true metabolisable energy infeedingstuffs.Poult.Sci.55:303308.Sibbald, I. R. 1979. Theeffectofthedurationoftheexcretacollectionperiodonthetruemetabolizableenergyvalues offeedingstuffswithslowratesof passage. Poult. Sci. 58: 896899.Sibbald, I. R. 1982. Measurement of bioavailable energyinpoultryfeedingstuffs: Areview. Can. J. Anim. Sci. 62: 9831048.Tzeng, R. Y. andBecker, W. 1981. Growthpatternsofbodyandabdominal fat weightsinmalesbroilerschickens. Poult.Sci.60:11011106.Urdaneta, M. and Leeson, S. 2004. Effect of dietary crudeproteinandlysineonfeathergrowthinchickstotwenty-onedaysofage.Poult.Sci.83:17131717.VanMilgen, J., Bernier, J. F., LeCozler, Y., Dubois, S. andNoblet, J. 1998. Major determinants of fasting heat productionand energetic cost of activity in growing pigs of different bodyweight and breed/castration combination. Br. J. Nutr. 79: 509517.VanMilgen,J.,Noblet,J.,Dubois,S.,Carre,B.andJuin,H.2001. Utilizationofmetabolizableenergyinbroilerchickens.Poult.Sci.80(Suppl.1):170(Abstr.).Van Milgen, J., Noblet, J. and Dubois, S. 2001. Energeticefciencyof starch, protein, andlipidutilizationingrowingpigs.J.Nutr.131:13091318.Wenk, C., Colombani, P. C., VanMilgen, J. andLemme, A.2001. Glossary: Terminology in animal and human energymetabolism. Pages 409421 in A. Chwalibog and K. Jakobsen,eds. Proceedings of the 15th on Energy Metabolism inAnimals. EAAP Publ. no. 103. Wageningen Pers, Wageningen,theNetherlands.Whitehead, C. C. 1990. Responses of body composition,growthandfoodefciencytodietaryproteiningeneticallyleanandfatbroilersuptosevenweeksofage.Br.Poult.Sci.31:163172.Whitehead, C. C. andGrifn, H. D. 1984. Development ofdivergentlinesofleanandfatbroilersusingplasmaverylowdensitylipoproteinconcentrations as selectioncriterion: therstthreegenerations.Br.Poult.Sci.25:573582.Wilson, B. J. 1977. Growthcurves: their analysis anduse.Pages 89115 in K. N. Boorman and B. J. Wilson, eds. Growthandpoultry meat production. BritishPoultry Science Ltd.,Edinburgh,UK.Wiseman, J. and Lewis, C. E. 1998. Inuence of dietary energyandnutrientconcentrationonthegrowthofbodyweightandLOPEZANDLEESON *ENERGYPARTITIONINGINBROILERCHICKENS 211carcass components of broiler chickens. J. Agric. Sci. 131: 361371.Znaniecka, G. 1967. Caloricvalueofproteinandfatofthechickens body. Pages 407408 in K. L. Blaxter, J. Kiela-nowski, andG. Thorbek, eds. Proceedingof the4thEAAPSymposiumonEnergyMetabolismof FarmAnimals. New-castle-upon-Tyne,UK.Zubair,A.K.andLeeson,S.1994.Effectofvaryingperiodofearly nutrient restriction on growth compensation and carcasscharacteristicsofmalebroilers.Poult.Sci.73:129136.212 CANADIANJOURNALOFANIMALSCIENCE