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Rev Colomb Cienc Pecu 2018; 31(4):276-284

276

Revista Colombiana de Ciencias Pecuarias

Original articles

A step-up ractopamine feeding program for finishing pigs¤

Niveles incrementales de ractopamina para cerdos en ceba

Plano de níveis aumentados de ractopamina para suínos em terminação

Tiago L Holzback1, Zoot; Anderson Corassa1*, Zoot, PhD; Charles Kiefer2, Zoot, PhD; Alexandre O Teixeira3, Zoot, PhD; Leonardo M Moreira3, Quím, PhD; Carlos M R Junior4, Zoot, MSc.

1Programa de Pós Graduação em Zootecnia, Universidade Federal de Mato Grosso, Campus de Sinop. Avenida Alexandre Ferronato Nº 1.200, Setor Industrial CEP 78557-267, Sinop, MT, Brasil.

2Universidade Federal de Mato Grosso do Sul, Av. Senador Filinto Müller Nº 2443 - Caixa Postal 549, Bairro Vila Ipiranga, CEP 79070-900, Campo Grande, MS, Brasil.

3Universidade Federal de São João Del Rei, Departamento de Zootecnia. Praça Frei Orlando, 170, Centro, CEP 36307-352, São João Del-Rei, MG, Brasil.

4Universidade Federal de Lavras, Campus Universitário, Caixa Postal 3037, CEP: 37200-000, Lavras, MG, Brasil.

(Received: November 12, 2016; accepted January 28, 2018)

doi: 10.17533/udea.rccp.v31n4a04

¤ Tocitethisarticle:HolzbackTL,CorassaA,KieferC,TeixeiraAO,MoreiraLM,JuniorCMR.Astep-upractopaminefeedingprogramforfinishingpigs.RevColombCiencPecu2018;31(4):276-284.

* Correspondingauthor:AndersonCorassa.ProgramadePósGraduaçãoemZootecnia,UniversidadeFederaldeMatoGrosso,CampusdeSinop.AvenidaAlexandreFerronatoNº1.200,SetorIndustrialCEP78557-267,Sinop,MT,Brasil.Tel.:+556698423-5671.E-mail:[email protected].

Abstract

Background:Ractopamine(RAC)supplementationinthefeedhasbeenevaluatedasastrategytoincreaseproductiveefficiencyinfinishingpigs.Objective:ToevaluatetheeffectsofdifferentRACdietarylevelsonperformance,carcasstraits,efficiencyoflysine(ELU)andenergy(EEU)utilization,andeconomicviabilityinfinishingpig.Methods: Atotalof40barrows(74.75±5.22kg)werefedfourRAClevels(0,5,10and5-10mg/kg step-upprogram)from0-14,15-31and0-31days.Performance,carcasscharacteristics,ELU,EEU,costperunitofweightgain(CWG),paymentandprofitparametersweremeasured.Theanimalsweredistributedinacompletelyrandomizeddesigninfourtreatments,withtenreplicatespertreatment.Theexperimentalunitwas each animal. Results: PigsfedRACdietsshowedincreasedbodyweightsat14and31days,averagedailygain(ADG)at0–14and0–31days,ELUat0-14days,andhotcarcassweightascomparedwiththosefedthecontroldiet.Thestep-upprogramascomparedtothe10mg/kg RAC concentration resulted in increased bodyweight,feed/gainratio(FGR),ADG,ELU,EEUandCWGat0–14days.PaymentbyweightandbonuspaymentwerebetterfortreatmentswithRACascomparedtocontrol.Conclusions: PigsfedRACimproved

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A Step-up ractopamine program for pigs

performance,carcassweight,ELU,EEUandeconomicviability.Theresultswerebetterforthestep-upprogramcomparedwiththeintermittentuseof10mg/kg RAC.

Keywords:beta-adrenergic agonist, carcass quality, economy, lysine, pig nutrition.

Resumen

Antecedentes:Lasuplementacióndecerdosconractopamina(RAC)esunaestrategiaparaaumentarlaeficienciaproductivaenceba.Objetivo: EvaluarelefectodediferentesplanesdesuplementaciónconRACendietasdecerdosencebasobreelrendimientoproductivo,característicasdelacanal,eficienciadeutilizacióndelisina(ELU)yenergía(EEU),yviabilidadeconómica.Métodos:Untotalde40machoscastrados(74,75±5,22kg)fueronalimentadosconcuatronivelesdeRAC(0,5,10y5-10mg/kgdeplanoescalonado)de0-14,15-31y0-31días.Seevaluóelrendimiento,característicasdelacanal,ELU,EEU,elcostoporunidaddegananciadepeso(CWG),lostiposdepagoyganancias.Losanimalessedistribuyeronenundiseñocompletamentealeatorizadoencuatrotratamientos,condiezrepeticionesportratamiento.Launidadexperimentalfuecadaanimal. Resultados:LosanimalessuplementadosconRACtuvieronmayorpesocorporalalos14y31días,gananciadepesodiaria(ADG)de0-14y0-31días,ELUde0-14díasypesodelacanalcalienteencomparaciónconelgrupocontrol.Encomparaciónconlaconcentraciónde10mg/kgdeRAC,elplanoescalonadoresultóenunaumentodepesocorporal,conversiónalimenticia(FGR),ADG,ELU,EEUyCWGalos0-14días.ElpagoporpesoyelpagoporbonificaciónfueronmejoresparalostratamientosconRACencomparacióncon el control. Conclusiones:LoscerdosencebaalimentadosconRACtienenmejorrendimiento,pesodelacanal,ELU,EEUyviabilidadeconómica.Losresultadosdelosparámetrosestudiadossonmejoresconelusodelplanoescalonadoencomparaciónconelusocontinuode10mg/kgdeRAC.

Palabras clave:agonista beta-adrenérgico, calidad de la canal, economía, lisina, nutrición de cerdos.

Resumo

Antecedentes:Suplementaçãoderactopamina(RAC)emdietasparasuínosfoiavaliadacomoumaestratégiaparaaumentareficiênciadeproduçãodesuínosemterminação.Objetivo:AvaliarosefeitosdediferentesplanosdesuplementaçãodeRACemdietasparasuínosemterminaçãosobreodesempenho,característicasdecarcaça,eficiênciadeutilizaçãodelisina(ELU)eenergia(EEU),eviabilidadeeconômica.Métodos: Umtotalde40machoscastrados(74.75±5.22kg)foramalimentadoscomquatroníveisdeRAC(0,5,10e5-10mg/kg planoescalonado)em0-14,15-31e0-31dias.Desempenho,característicasdecarcaça,ELU,EEU,custoporunidadedeganhodepeso(CWG),tiposdepagamentoelucroforammensurados.Osanimaisforamdistribuídosemumdelineamentointeiramentecasualizadoemquatrotratamentos,dezrepetiçõesparacadatratamento.Aunidadeexperimentalfoicadaanimal. Resultados: Os animais alimentados com dietas contendo RACmostraramaumentodepesocorporalaos14e31dias,ganhodepesodiário(ADG)de0-14e0-31dias,ELUde0-14diasepesodecarcaçaquentecomparadoaogrupocontrole.Oplanoescalonadocomparadoaonívelde10mg/kgdeRACmostroumaiorpesocorporal,conversãoalimentar(FGR),ADG,ELU,EEUeCWGde0-14dias.PagamentoporpesoepagamentoporbonificaçãoforammelhorparatratamentoscomRACemcomparaçãoaocontrole.Conclusões: SuínosalimentadoscomRACmostrammelhordesempenho,pesodecarcaça,ELU,EEUeviabilidadeeconômica.Osresultadosdosparâmetrosestudadosforammelhorescomusodoplanoescalonadoquandocomparadocomusoconstantede10mg/kgdeRACparasuínosemterminação.

Palavras chave:agonista beta-adrenérgico, economia, lisina, nutrição de suínos, qualidade de carcaça.

Introduction

Ractopamine (RAC) is a β-adrenergic agonistfeed additive that increases the efficiency of porkproduction(Carret al.,2008)byimprovingcarcassleanness.This substance acts on the β-adrenergicreceptorsofmusclecellsincreasingthediameterofthefibers,andthereby,themusclemass.Inadipocytecells, RAC acts by catalyzing the breakdown of

triglycerides,inhibitinglipogenesisandstimulatinglipolysis (Mills, 2002), consequently reducing fatdeposition.Overall,RAChas shown tomaximizeprotein depositionwithout changingmeat qualitystandards such as color,marbling, firmness or pH(KieferandSanches,2009).

Animal response toRAC varies according toseveralaspects;e.g.,levelofdietarysupplementation

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(Corassa et al., 2010), feeding duration (Oliveira et al., 2013; Almeida et al., 2013), and nutritional level (Marinho et al.,2007).Theeffectsoffeedingdurationand supplementation level have been discussed intermsofthestimuli-dependentanddesensitizationofreceptorresponses(Moodyet al., 2000).

Ractopamineistypicallyrecommendedforpigsinthefinishingphasewithin5to20mg/kgrange(Brazil,2010)during the last3 to5weeksbefore slaughter(Amim et al.,2014).AfterfourweeksofdietaryRACsupplementation,a reduced intensityof the responseduetodown-regulationanddesensitizationofreceptorshasbeenreported(Armstronget al.,2004).OnewaytominimizethereductionofRACresponseisbyincreasingthedosageaftertwoweeksofsupplementation(Moody,2000);thissupplementationstrategyisknownasstep-up.Dietarylevelsofdigestiblelysineandmetabolizableenergyinfluenceperformanceandcarcasscharacteristicsoffinishingpigs(Andrettaet al., 2011), so knowledge about theefficiencyof thesenutritional factorsasafunctionofRAClevelscouldaffecttheviabilityofthisadditive.

Therefore, the hypothesis tested in the presentstudywasthataRACstep-upfeedingprogramcouldimproveperformanceandcarcassleannessinfinishingpigscomparedtodietswithoutRACorwithonlyonelevelofRAC.Therefore,theobjectiveofthisstudywastoevaluatetheeffectsofdifferentRACfeedinglevels on performance, carcass traits, efficiencyoflysine (ELU) and energy utilization (EEU), andeconomicviabilityoffinishingpigs.

Material and Methods

Ethical considerations

ThestudywasconductedatCampusUniversitáriode Sinop,Universidade Federal deMatoGrosso,Brazil, following ethical principles for animalexperimentationadoptedby theNationalCouncil forAnimalExperimentationControl,approvedbytheEthicsCommitteeonAnimalUseofUniversidadeFederaldeMatoGrosso(protocoln.23108.700673/14-4).

Husbandry and diets

Thetrialsiteislocatedat12°36ʹ77.20”Slatitudeand56°74’75.70”Wlongitude.

Commercial hybrid barrows (n = 40) of highgenetic potential for lean gain, single geneticorigin (Agroceres PIC®), with 74.75 ± 5.22 kginitial bodyweightwere used.The animalsweredistributedinacompletelyrandomizeddesignintofourtreatmentsandtenreplicatespertreatment.Thetreatmentswereasfollow:control(basaldietwithoutRACfor31d);5mgkg-1(basaldietsupplementedwith5mg/kgRACfor31d);10mg/kg(basaldietwith10mg/kgRACduring31d);andstep-up(basaldietwith5mg/kgRACduring14dfollowedofbasaldietwith10mg/kgRACduring15to31d).

Pigswere fed dietary treatments andwaterad libitum.Basalisoenergeticandisonitrogenousdietswere formulated based on corn and soybeanmeal(Table 1) to meet the minimum recommendations proposed in the food composition tables andnutritional requirements ofRostagnoet al. (2011). The animals were housed in a shed (3.40 m height) withconcretefloor.

Data collection

The trial lasted 31 days, and the animalswereweighed and their feed intake and leftovers were measuredatthebeginning,onthefourteenthdayandattheendofthetrialforeconomicandperformanceevaluations.Pigperformancewasevaluatedthroughaveragedailyfeedintake(ADFI),averagedailygain(ADG),andfeed/gainratio(FGR)at0,14th and 31th days,byweighingtheanimalsaswellasfeedleftovers.Animal performance datawere used to calculateefficiencyof lysine (ELU,g/kg) and energy (EEU,Mcal/kg)utilizationobtainedfordailylysine(g),orenergy(Mcal)intakedividedbydailyweightgain.

Attheendofthetrial,allanimalswereidentifiedwithtattoos,fastedoffeedfor12handthentransportedtotheslaughterhouse(450kminabout6h).Animalswere stunned before slaughter. The carcasses were washed,weighted,splitalongthedorsalmidlineandthencooledto7°Cfor24h,accordingtotheBrazilianCarcassClassificationMethod(ABCS,1973).Loineyearea(LEA),loindepth(LD)andbackfatthickness(BT)weremeasured.TheLEAassessmentfollowedmethodologybyBoggsandMerkel(1979)usingthesection between the 10th and 11thribsofthelefthalf-side. The outline of the Longissimus dorsi muscle

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Carcassleanpercentage(%)=60–(BT×0.58)+(LD×0.10)

Carcassleanamountwasdeterminedas:

Carcassleanamount(kg)=(hotcarcassweightxcarcassleanpercentage(%))/100

To calculate the carcass bonus index, the following equationwasused(Guidoni,2000):

Bonusindex=23.6+0.286×carcassweight+leanmeatpercentage

To analyze economic viability, feed cost (FC)/kgofweightgain(CWG)wasdeterminedusingthefollowingequation(Bellaveret al.,1985):

CWGi=(QixPi)/Gi

Where:

Yi:FC/kgweightgainofpigsintheith treatment.Pi:price/kgfeedintheith treatment.Qi:quantityoffeedconsumedintheith treatment.Gi:weightgainofpigsintheith treatment.

Economicviabilityconsideredpigpaymentbasedonweight/pig(PAYWEIGHT),consideringR$3.00/kg.Revenue from the payment of each animal byweight was also calculated, which added to the bonus value (PAYBON).Additionally, profit frompigsaleswascalculatedconsideringPAYWEIGHT(PROFITWEIGHT),asfollows:

PROFITWEIGHT=PAYWEIGHT–[(initialweightxbaseprice)+(feedintake/dayxperiodindaysx

feedprice)]

Todetermineprofitobtainedfromthesaleoftheanimals,thePAYBON(PROFITBON)wasusedasfollows:

PROFITBON=PAYBON–[(initialweightxbaseprice)+(feedintake/dayxperiodindaysxfeed

price)]

Dietary cost/kg of ingredients were: corn(R$ 0.25), soybeanmeal (R$ 1.15),mineral and

Table 1. Calculated composition of the experimental diets (g/kg).

Ingredient Ractopamine (RAC) inclusion (mg/kg)

0 5 10

Corn 728.80 728.55 728.80

Soybean meal 243.00 243.00 243.00

Mineral and vitamin mix¹ 25.00 25.00 25.00

Aminoacid compound² 3.20 3.20 3.20

Ractopamine³ - 0.25 0.50

Nutritional composition

Metabolizable energy (kcal/kg) 3,227 3,227 3,227

Crude protein 174.1 174.1 174.1

Ether extract 30.3 30.3 30.3

Crude fiber 27.5 27.5 27.5

Mineral matter 47.1 47.1 47.1

Calcium 07.2 07.2 07.2

Available phosphorus 02.5 02.5 02.5

Digestible lysine 09.0 09.0 09.0

Digestible methionine 02.6 02.6 02.6

Digestible methionine+cistine 05.2 05.2 05.2

Digestible threonine 05.9 05.9 05.9

Digestible tryptophan 01.7 01.7 01.7

Digestible arginine 10.3 10.3 10.3

Digestible valine 07.1 07.1 07.1

Sodium 01.8 01.8 01.8

1Composition per kg of diet: Cu (8,0 mg), Fe (25,8 mg), Zn (82 mg), Mn (24 mg), Se (0,22 mg), I (0,66 mg), Co (8 mg), cholin (120 mg), vitamin A (2,960 IU), vitamin D3 (740 IU), vitamin E (5,365 IU), vitamin K3 (0.37 mg), nicotinicacid (8,87mg), pantothenicacid (5,44 mg), folicacid (0,22 mg), biotin (0,018 mg), thiamin (0,74 mg), riboflavin (2.07 mg), pyridoxine (0.74 mg), cyanocobalamin (11 µg), phytase (500 FTU), zinc-bacitracin (55 mg).2Composition per kg of diet:digestible lysine (1.344 g), digestible methionine (0.192 g),digestible threonine (0.081 g).3Composition per kg of product: ractopamine hydrochloride 20 g.

was drawnon transparent acetates for subsequentdetermination of the area using the AutoCAD program.TheLDwasmeasureddirectlyinthesamesectionof themuscle representedbyan imaginaryline, corresponding to the largest diameter of theexposedsurfaceofthemuscle.TheBTwasmeasuredin the same section of the muscle used to determine LEA,perpendiculartotheskin,butexcludingit.Bothmeasurementsweretakenwithacaliper.

Carcass leanpercentagewasdeterminedby thefollowingequation(BridiandSilva,2007):

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vitaminmix(R$1.70),aminoacidmixture(R$5.67),ractopamine(R$55.00).Costs/kgoffeedwere:basal(R$0.5221),5mg/kg(R$0.5357)and10mg/kg(R$0.5495).At the end, values of economic analysiswereconvertedtoUSdollars,consideringR$3.00=US$1.00.

Statistical analysis

DatawassubmittedtoanalysisofvarianceusingtheGLMprocedureofSAS® software,version6(SASInstitute, Inc.,Cary,NC,USA) (2001), using theinitialweightascovariateandthemeandecomposedfactors into orthogonal contrasts: i)without-RACversuswith-RAC,ii)5mg/kgversus10mg/kgRAC,and;iii)10mg/kgversus5–10mg/kg(step-up)RAC.Differences between levels of fixed effects were consideredsignificant(p≤0.05),ortendency(p<0.10).

Results

Performance

ThepigssupplementedwithdifferentRAClevelsshowedincreased(p<0.05)weightat14and31days(lastday),aswellasADGform0–14days,and0–31days of the trial, compared to those in the controlgroup(Table2).DietaryinclusionofRACshowednoeffectonweightgainonlywithin15–31days.TheRACdidnotinfluence(p>0.10)ADFIincomparisontothecontrolgroup.Feedgainratio(FGR)ofpigsfedRACshowedatendencyforbetterresultsinthe0–14(p=0.07),and0–31days(p=0.09).Nodifferencewasobservedinperformance(p>0.10)ofpigsfed5or10mg/kgRAC.Thestep-upRACprogramresultedinbetter(p<0.05)weight,ADGandFGRinthe0–14dayscompared to10mg/kgRAC. Inaddition, thestep-upshowedtendenciesofincreasedweight(p=0.09)forADG(p=0.09)andFGR(p=0.08)inthe0-31days.

Efficiency of lysine (ELU) and energy (EEU) utilization

TheELUduring0–14dayswashigher(p<0.05)inpigsfedRACcomparedtothecontroltreatment(Table 3).No differencewas noted in ELUwithrespectto5to10mg/kgRACtreatments.Thestep-upprogramimproved(p<0.05)ELUduring0–14,and0-31daysincomparisonto10mg/kgRAC.Similarly,EEUduring0–14daysshowedatendency(p=0.07)toimproveinpigsfedRACcomparedtothecontrol.NodifferencewasobservedinEEUwithrespectto5to10mg/kgRAC.Thestep-upprogramimproved(p<0.05)EEUduring0–14daysincomparisonto10mg/kgRAC.TheotherparameterswerenotaffectedbyRAC.

Carcass characteristics

TheRACincreasedhotcarcassweight(p<0.05)andtended(p=0.09)toincreaseLEAcomparedwiththecontrolanimals(Table4).TheBT,LD,carcasslean percentage, carcass lean amount and bonuspaymentwerenotinfluencedbyRAC(p>0.10).

Comparison between5 versus 10mg/kgRAC,and10versus5–10mg/kgRAChadnoeffectsoncarcass traits (p>0.10).A tendency for a greatercarcassweightinpigsfedthestep-upprogram(p=0.09)wasobservedincomparisonwiththosefed10mg/kgRAC(Table4).Theothercarcassparameterswerenotinfluencedbythetreatments.

Economic viability

The PAYWEIGHT and PAYBONwere higherforpigsfedRACcomparedtothecontrols,withatendency(p=0.09)forimprovedPROFITWEIGHT(Table5).Nodifferencewasobservedineconomicviabilitycomparing treatmentswith5or10mg/kgRAC.The cost per unit ofweight gain (CWG) inpigsfed5–10mg/kgRAC(step-up)waslower(p<0.05) in comparison to those fed 10mg/kgRACduring0-14and0-31days.Inaddition,atendencyforimprovementwasnotedforPAYWEIGHT(p=0.09),PAYBON (p=0.09), PROFITWEIGHT (p=0.07),andPROFITBON(p=0.08)inthestep-upprogram.

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Table 2. Performance of finishing pigs supplemented with Ractopamine (RAC).

Parameters1 RAC (mg/kg) ContrastsCV (%)0 5 10 5-10 0 vs others 5vs10 10vs5-10

Weight (kg)

Day 0 76.12 75.55 74.61 72.74 0.37 0.83 0.26 7.39

Day 14 86.45 89.01 87.04 89.20 0.01 0.28 0.03 2.38

Day 31 104.46 108.30 106.12 109.11 0.02 0.65 0.09 3.57

Interval I (0-14 days)

ADFI (kg/day) 2.86 3.00 2.93 2.89 0.80 0.71 0.54 12.30

ADG (kg/day) 0.83 1.03 0.88 1.03 0.01 0.22 0.03 15.96

FGR (kg/kg) 3.43 2.92 3.34 2.81 0.07 0.38 0.03 16.03

Interval II (15-31 days)

ADFI (kg/day) 2.55 2.67 2.57 2.57 0.35 0.65 0.37 17.65

ADG (kg/day) 1.06 1.12 1.12 1.17 0.34 0.74 0.63 19.67

FGR (kg/kg) 2.42 2.40 2.30 2.20 0.82 0.75 0.78 22.06

Total interval (0-31 days)

ADFI (kg/day) 2.69 2.82 2.73 2.72 0.55 0.67 0.47 8.50

ADG (kg/day) 0.96 1.08 1.01 1.11 0.02 0.71 0.09 11.89

FGR (kg/kg) 2.82 2.62 2.70 2.45 0.09 0.89 0.08 11.711ADFI: average daily feed intake; ADG: average daily gain; FGR: feed/gain ratio.

Table 3. Efficiency of lysine (ELU) and energy utilization (EEU) of finishing pigs supplemented with Ractopamine (RAC).

RAC (mg/kg) Contrasts

0 5 10 5 - 10 0 vs Others 5 vs 10 10 vs 5-10 CV (%)Lysine utilization efficiency (g/kg)

0-14 days 30.76 26.99 31.47 25.95 0.02 0.15 0.01 13.13

15-31 days 21.96 21.94 21.64 21.05 0.68 0.58 0.64 12.41

0-31 days 25.22 24.91 23.77 22.45 0.10 0.94 0.03 10.85

Energy utilization efficiency (Mcal/kg)

0-14 days 11.18 9.67 11.08 9.40 0.07 0.38 0.03 16.03

15-31 days 7.88 7.87 7.77 7.55 0.82 0.75 0.79 22.06

0-31 days 9.11 8.53 8.85 8.09 0.10 0.89 0.11 11.71

Table 4. Carcass traits of finishing pigs supplemented with Ractopamine (RAC).

RAC (mg/kg) Contrasts0 5 10 5 - 10 0 vs Others 5 vs 10 10 vs 5-10 CV (%)

Hot carcass weight (kg) 83.57 86.63 84.89 87.29 0.02 0.65 0.09 3.57

Backfat thickness (mm) 13.40 14.64 13.97 13.80 0.51 0.52 0.90 21.35

Loin depth (mm) 71.99 69.31 73.41 75.32 0.82 0.13 0.62 11.51

Loin eye area (cm²) 54.59 56.68 57.79 58.68 0.09 0.42 0.70 8.70

Carcass lean amount (kg) 49.65 50.58 50.32 51.99 0.16 0.56 0.15 4.89

Carcass lean (%) 59.42 58.44 59.24 59.53 0.60 0.19 0.73 3.10

Carcass bonus index (%) 106.93 106.81 107.12 108.09 0.59 0.34 0.31 1.94

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Table 5. Cost per unit of weight gain (CWG), payment, and profit of finishing pigs supplemented with Ractopamine (RAC).

ParametersRAC (mg/kg) Contrasts

CV (%)0 5 10 5 – 10 0 vs Others 5 vs 10 10 vs 5-10Cost per unit of weight gain (CWG) (US$/kg)

0-14 days 0.603 0.533 0.630 0.520 0.22 0.27 0.01 16.07

15-31 days 0.423 0.437 0.440 0.427 0.78 0.98 0.78 22.32

0-31 days 0.503 0.480 0.527 0.470 0.54 0.45 0.04 11.93

Payment (US$/pig)

PAYWEIGHT 104.47 108.29 106.12 109.11 0.02 0.65 0.09 3.57

PAYBON 111.39 115.10 113.23 117.20 0.05 0.96 0.09 4.52

PROFITWEIGHT 15.20 17.93 15.85 19.12 0.09 0.77 0.07 22.45

PROFITBON 22.13 24.74 22.97 27.21 0.14 0.86 0.08 21.27PAYWEIGHT: revenue obtained by the payment of each animal per weight; PAYBON: revenue obtained by the sale of each animal per weight adding the bonus index; PROFITWEIGHT: profit, considering the PAYWEIGHT; PROFITBON: profit, considering the PAYBON.

Discussion

Performance

ImprovementinweightandADGinpigsfedRACis related to the mode of action of this substance, whichincreasesmuscle,minimizingfatdeposition.This effectwas also reported byMarinho et al. (2007),andCantarelliet al.(2009)withimprovedfinal weight,ADG and FGR of pigs with RACsupplementation, in addition to improvedcarcasscharacteristics by reducing BT and increasingdeposition rate of leanmeat. Reviewing data onthe use of RAC, Andretta et al.(2011)reportedthatRACincreased14and11%thevaluesofobservedand calculated FGR, respectively. Similarly,Almeida et al.(2013),evaluatingdifferentfeedingperiodsusing10mg/kgRAC,observednoeffectofRAConADFI,noronbackfatmeasurements.ThelackofRACeffectonfeedintakecouldbeduetothefactthatthelevelsproposedinthisstudywerenotsufficienttoinfluencethisparameter.Incontrast,Crome et al.(1996)observeddecreasedfeedintakewhenhigherdietaryRAClevelswereused.Ontheotherhand,no influenceofup to20mg/kgRAConADFIwasreported in thestudyofKieferandSanches(2009).

A similarity of responses between the twoRAClevels(5mg/kg versus 10 mg/kg) contradict apreviousstudybyMarinhoet al.(2007),whichevidenceddifferences,representedbytheclassicaldose-dependent response. Corassa et al. (2013)

reportedthatdeficiencyinlysineusingRACcanlimitanimalresponse,asthisaminoacidishighlyrelevantforproteinsynthesis,andavailablelysineaffectspigperformance.Therefore,theperformanceof animals fed 10 mg/kg could have been limited bythedietarylysinelevel.Inthissense,Rostagnoet al. (2011)suggestusingdifferent lysinelevelsasafunctionofdietaryRACconcentration,whichwas not considered in this study. Our findingsare inconsistent with other studies comparingthestep-upprogramversuscontrol.Polettoet al. (2009)showedthatresultsfromthefirst2weeksofthestudy,whenRACwasfedat5mg/kgdidnotshowdifferencesingrowthperformancebetweencontrol and RAC animals, but when the RAC level wasincreasedto10mg/kg,RAC-fedanimalshadgreaterADG,G:F, andBWat d28 compared tothe control pigs. In the study byRikard-Bell et al.(2009),thestep-upreducedADFIduring0-14daysincreasedADGinthe15-31,and0-31days,improved G:F and body weight at 31 days, inadditiontoimprovedcarcassweight,carcassleanamount and percentage. Garbossa et al. (2013) evaluated 0 to 20 mg/kg RAC, observing a linear increase in final weight with increasing RAC levels, aswell as in average dailyweight gain.Interestingly,theyregisteredimprovementinfeedconversionwith optimal level for 5mg/kg,withnoeffectonintakeofdigestiblelysineandenergy.

Theresponsesrecordedforthestep-upprograminthepresentstudyconfirmtheabilityoftheanimalsto enhance the mode of action of the additive, as

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evidenced by an increase in stimulation of cellreceptors (Armstronget al., 2004), suggesting that thestep-upprogrammaygivebetterresultsthanthecontinued use of a single high concentration.

Efficiency of lysine and energy utilization

Efficiencyinlysineandenergyutilizationresultsare related to RAC mode of action, which enhances tissue protein accretion at the expense of adiposetissue. In turn,pigs fedRACrequireoptimizationof lysine intake and dietary energy content.Aslysineisthefirstlimitingaminoacidforpigs,lysineinclusion should be increased in diets containing RAC.Moreover, adjustments of the other aminoacidsasa functionof lysineshouldbeconsideredin the formulation of these diets (Yen et al.,1990).Accordingly, Ferreira (2014) also demonstratedimprovedefficienciesoflysineandenergyutilizationin diets containing RAC in comparison with acontroldiet.ImprovednutrientutilizationbyRAC-fed animals is in linewith higher bodyweight,carcass weight and weight gain, due to increased proteinsynthesisandpartial lipogenesisblockade,characteristic of RAC mode of action (Schinckel et al., 2003), due to gain variations (fat, lean, and bone) andmaintenance requirements influencing energyconversion (Patience et al.,2015).

Carcass characteristics

The increase in carcass weight results from the increased weight of the animals at the end of the experimentalperiod.The influenceofRACuseoncarcass traits remains unclear; Pereira et al. (2008) reportedimprovementinsomeparameters,includingthose evaluated in this study,whileMarinhoet al. (2007)andSanchezet al.(2010)reportednoeffect.TheRAClevelsusedinthisstudymaynothavebeensufficienttoexpresstheeffectsoncarcasstraits,sinceCorassa et al. (2010) showed that lower levels of RAC usually improve performance,while higher levelsimprovecarcasscharacteristics.

The results of animal weight and carcass traits in the step-upprogramscompared to10mg/kgRACagreewiththosebyFerreira(2014),buttheydiffercomparedtothosebyCorassaet al. (2010).

Economic viability

DietswithoutRACusually have lower aminoacidandenergylevelsthanRACdiets(Rostagnoet al.,2011),possiblygenerating lowerfinancialcostandperformance,andimpactingthecostperunitofgain.However,inthepresentstudy,nodifferencewasobserved among diets with the same nutritional levels.

ThePAYWEIGHTandPAYBONwerehigherforanimalsfedRACascomparedwiththosenotfedRACbecause animals had increasedfinal bodyweight,whichhasadirectimpactonthefinalsalevalue.

Inconclusion,RACuseandthestep-upprogramimproveperformanceparameters,carcasscompositionandeconomicviabilityoffinishingpigs.

Conflicts of interest

The authors declare they have no conflicts ofinterestwith regard to thework presented in thisreport.

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