Impact of replacing soybean meal in beef cattle diets with inactive dry yeast, a sugarcane by-product of ethanol distilleries and sugar mills

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ContentslistsavailableatScienceDirect

Animal

Feed

Science

and

Technology

journalhomepage:www.elsevier.com/locate/anifeedsci

Impact

of

replacing

soybean

meal

in

beef

cattle

diets

with

inactive

dry

yeast,

a

sugarcane

by-product

of

ethanol

distilleries

and

sugar

mills

Andressa

Fernanda

Campos,

Odilon

Gomes

Pereira

∗

,

Karina

Guimarães

Ribeiro,

Stefanie

Alvarenga

Santos,

Sebastião

de

Campos

Valadares

Filho

UniversidadeFederaldeVic¸osa,DepartamentodeZootecnia,Vic¸osa36571-000,MinasGerais,Brazil

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received25June2013

Receivedinrevisedform4January2014 Accepted6January2014 Keywords: Digestibility Nutrient Rumen-degradableprotein

a

b

s

t

r

a

c

t

Thisstudyassessedtheintake,totalandpartialapparentdigestibilityofnutrients,pH, rumi-nalammoniaconcentration,nitrogenefficiencyusage,andproductiveperformanceofbeef cattlefedwithdifferentsoybeanmealreplacementlevelswithinactivedryyeast(IDY0, 250,500,750,and1000g/kg).Theforage:concentrateratiowas60:40andtheforagesource wascornsilage.Concentrateswereformulatedtocomprise220.0g/kgCPindependentof treatments.Inthefirstexperiment(EXP1),35Nelorebullswithaninitialaverageweightof 370±42kgweredistributedacrossacompletelyrandomizeddesign,withfivetreatments andsevenreplicatestoassessnutrientintakeandperformance.EXP1lasted98daysand wasdividedintoa14-dayadaptationperiodandthreeexperimentalperiodsof28days each.Inthesecondexperiment(EXP2),fivecastratedNeloresteerswithaninitialaverage weightof320±39kgwerefistulatedintherumenandabomasumanddistributedina 5×5Latinsquaredesign,balancedforresidualeffect.Thepurposeofthisexperimentwas toassessthetotalandpartialdigestibilityofnutrients,pH,ruminalammonianitrogen,and nitrogenefficiencyofusage.EXP2lasted90days,dividedintofiveexperimentalperiods. Eachperiodlasted18daysandwasdividedinto10daysforadaptationtothedietsand8 daystocollectsamples.Theintakeofdrymatter(DMI)decreasedlinearly(P=0.03)with increaseddietaryIDYlevels.Conversely,theintakeofneutraldetergentfiberassayedwith aheat-stableamylaseandcorrectedforashandnitrogenouscompounds[aNDFom(n)]in g/day(P=0.043),andtheg/kgbodyweight(P=0.011)increasedlinearlyasIDYwasaddedto theconcentrate.Theexperimentaldietsshowednoeffect(P>0.05)onthetotalandpartial apparentnutrientdigestibility.IDYhadnoeffect(P>0.05)onruminalpH,ruminal ammo-nianitrogen,ordietarynitrogenefficiency.Additionally,IDYhadnoeffectonproductive performancevariables,withtheexceptionofaveragedailygain(ADG),whichdecreased linearly(P=0.028)asIDYwasaddedtotheconcentrate.IDYadditionresultedindecreases

Abbreviations: RDP,rumendegradableprotein;IDY,Inactivedryyeast;ADG,averagedailygain;HCW,hotcarcassweight;FLW,finalliveweight; CADG,carcassaveragedailygain;DM,drymatter;OM,organicmatter;CP,crudeprotein;EE,etherextract;aNDFom(n),neutraldetergentfiberassayed withaheat-stableamylaseandcorrectedforashandnitrogenouscompounds;NDIN,neutraldetergentinsolublenitrogen;ADIN,aciddetergentinsoluble nitrogen;NFC,non-fibrouscarbohydrates;FDM,flowoffecaldrymatter;ADM,abomasaldrymatter;TDN,totaldigestiblenutrients;NB,nitrogenbalance; UUN,urinaryureanitrogen;NPN,non-proteinnitrogen;PUN,plasmaureanitrogen;Emic,microbialefficiency;PD,purinederivatives;BW,bodyweight; ILW,theinitialliveweight;DRS,dressingpercentageafterslaughter;RCY,carcassyield;Nmic,microbialnitrogencompounds;NID,normalindependent

distribution.

∗ Correspondingauthor.Tel.:+553138993323;fax:+553138992275. E-mailaddress:odilon@ufv.br(O.G.Pereira).

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inDMIandADGforbeefcattleinfeedlots(EXP2).However,theapparentdigestibilityof nutrientsandmicrobialefﬁciencywerenotaffected.Inaddition,IDYdidnotreducefeed conversionorcarcassgain.Thehighmarketpriceofsoybeanmealmightmakefeasibleits totalreplacementbyIDY,evenconsideringthepossibilityofasmallreductioninADG.

1. Introduction

Asaconsequenceofthehighcostofproteinsupplementsinfeedconcentrates,newnon-conventionalalternativeshave

beenexploitedinrecentyears.Bothethanoldistilleriesandbeerbrewerieshavesurplusyeastco-productsforuseinanimal

feed.Infeedlotdietsforbeefcattle,soybeanmealisthemostfrequentlyusedproteinconcentrateandisalsooneofthe

mostexpensiveproducts.Thesearchforalternativeproductsthatcanreplacesoybeanmealwithoutalteringbodyweight

gainandcarcassyieldisimportantforachievinghigherproﬁtsbyreducingthecostsofconcentrateingredients.Yeastsare

unicellularmicroorganismsthatgrowduringethanolfermentation(Yaraetal.,2006).Becauseoftheirproteincomposition

(300to450g/kg),yeastsarerichinlimitingaminoacidssuchaslysine,threonine,andmethionine,inadditiontovitaminB

complex(Ezequieletal.,2000).

Yeastproteinisclassiﬁedashavinghighrumendegradableprotein(RDP),whichmayresultinincreaseduseofreadily

availableenergysourcessuchasstarchforthesynthesisofmicrobialproteins,improvingproteinandenergysynchronization.

Yeastproteinhasahighruminaldegradabilitycomparedwithsoybeanmeal(990g/kgvs.790g/kgofRDP)(Marcondesetal.,

2009).Asaconsequence,Ruﬁnoetal.(2012)observedthatthegreatestamountofinactivedryyeast(IDY,Saccharomyces

cerevisiae)usedtosubstitutesoybeanmealresultedinthegreatestruminalammoniaproductioninlambs.IDYismarketed

bytheethanolandsugarproducingindustriesbecausethesurplusfromyeastmashcanbeusedasanalternativeingredient

inruminantdiets.Evaluationsofnutrientusebylivestockandtheresultingrumen-microorganisminteractionsareneeded

tobetterunderstandtherole ofthispotentialingredient.Thesedatacanbeobtainedthroughdigestionstudies,which

analyzethepossibilityofreplacingahigh-costconventionalfeedwithaby-productthatwouldotherwisebeconsideredan

environmentalcontaminant.

Thus,thepresentstudyaimedtoevaluatethepotentialnutritivevalueofIDYasaproteiningredientinruminantdiets

byassessingtheintake,totalandpartialdigestibility,pH,ruminalammonianitrogen,microbialefﬁciency(Emic),nitrogen

balance(NB),averagedailygain(ADG),carcassaveragedailygain(CADG),carcassyield,andfeedconversionwhenusing

differentsoybeanmealreplacementlevelsinthedietofNelorecattle.

2. Materialandmethods

2.1. Experimentalareaandclimaticconditions

ThisexperimentwasconductedintheExperimentation,ResearchandExtensionCenterofTriânguloMineiro(Central

deExperimentac¸ão,PesquisaeExtensãodoTriânguloMineiro,CEPET)oftheFederalUniversityofVic¸osa(Universidade

FederaldeVic¸osa,UFV),Brazil,fromJunetoSeptemberof2009.TheCEPETislocatedatanaveragealtitudeof620.2m,

18.41◦Slatitudeand49.34◦Wlongitude.TheclimateisclassiﬁedbyKöppenstandardsasAw,i.e.,hotandhumid,withthe

temperatureofthecoldestmonthabove18◦C,arainyseasoninthesummerandadryseasoninthewinter,withanannual

averageprecipitationofbetween1,400and1,600mm.

2.2. Experimentaldiets

Thedietswereformulatedtomeetbeefcattlerequirementsof1kgofdailygainaccordingtotheNationalResearch

Council(NRC,1996).Theforage:concentrateratiowas60:40onadrymatter(DM)basiswithcornsilageastheforage.The

dietsconsistedofﬁveconcentratereplacementlevelsofsoybeanmealbyIDY,0,250,500,750,and1000g/kgonDMbasis.

TheproportionsofconcentrateingredientsareshowninTable1,andthechemicalcompositionoftheconcentratesandcorn

silageisshowninTable2.

2.3. Animals,management,andsamplecollection

Themanagementandcareofanimalswereperformedinaccordancewiththeguidelinesandrecommendationsofthe

CommitteeofEthicsonAnimalStudiesattheFederalUniversityofVicosa(UFV),MG,Brazil.Todeterminenutrientintakeand

productiveperformance,35Nelorebullswithanaverageinitialbodyweight(BW)of370_±42kgweredistributedthroughout

acompletelyrandomizedexperimentaldesign,withﬁvetreatmentsandsevenreplicates(EXP1).Thetriallasted98daysand

wasdividedintoa14-dayadaptationperiodandthreeexperimentalperiodsof28dayseach.Fiveanimalswereslaughtered

attheendoftheadaptationtoestimatetheinitialcarcassweightsofallsteersatthebeginningoftheexperiment.They

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Table1

Ingredientproportioninexperimentalconcentrate(g/kg,wetbasis).

Ingredients Replacementlevels(IDYreplacingSBMg/kg)

0 250 500 750 1000

Groundcorn 774.7 776.9 779.0 781.2 783.4

Soybeanmeal(SBM) 184.2 138.5 92.7 46.5 –

Inactivedryyeast(IDY) – 43.7 87.5 131.5 175.9

Urea/ASa _10.9 _12.6 _14.1 _15.7 _17.4 Wheatmeal 12.5 10.7 9.0 7.3 5.5 Lime 5.5 5.5 5.5 5.5 5.6 Dicalciumphosphate 7.5 7.5 7.5 7.5 7.5 Sodiumchloride 4.4 4.4 4.4 4.4 4.4 Mineralmixb _0.3 _0.2 _0.3 _0.3 _0.3

a_Proportion_between_urea_and_ammonium_sulphate_(AS)_was₉_parts_of_urea_and₁_part_of_AS.

b _Copper_sulfate₍₂₂₅_g/kg),_cobalt_sulfate₍₁₄_g/kg),_zinc_sulphate₍₇₅₄_g/kg),_potassium_iodate₍₅_g/kg)_and_sodium_selenite₍₂_g/kg).

Animalswereweighedattheendoftheadaptationperiodand,following14hoffasting,werealsoweighedafterthelast

experimentalperiod.Feedwasprovidedintwodailymealsat8h00and15h00,andtheortswereweigheddailytoobtaina

maximumof50to100g/kgoftotalfeedprovidedasfreshfeed.Theortsweresampled,placedinlabeledbags,andstored

inthefreezerforlateranalysis.Thesilageandconcentratesweresampledthreetimesperweek.

Allsteerswereslaughteredattheendoftheexperimenttodeterminethedressingpercentage,whichwascalculatedas

thepercentagebetweenthehotcarcassweight(HCW)andtheﬁnalliveweight(FLW)afterfasting.Thus,thecarcassaverage

dailygain(CADG)wascalculatedbyusingthefollowingequation:

CADG

_kg day

=

FLW×

DRSf 100

−

ILW×

DRSi 100

n

whereFLWistheﬁnalliveweightafterfasting(kg),ILWistheinitialliveweightafterfasting(kg),DRSfisdressingpercentage

afterslaughterattheendoftheexperiment,DRSiisdressingpercentageafterslaughteredattheendoftheadaptationperiod

(beginningoftheexperimentalperiods),and“n”isthenumberofevaluateddays.

FivecannulatedNeloresteerswereusedtodeterminethetotalandpartialdigestibility,nitrogenuseefﬁciency,and

ruminalpHandammonialevels.Theanimalswereﬁstulatedintherumenandabomasum,andeachsteerhadanaverage

initialBWof320±39kg.Theyweredistributedacrossa5×5Latinsquaredesign(EXP2),balancedforresidualeffects

(Lucas,1957).Thefeedwasprovidedintwodailymealsat8h00and15h00inasufﬁcientquantitytoobtain5to10%orts.

Theﬁveexperimentalperiodslasted18daysandweredividedasfollows:10daysforadaptationtothediets;6daysto

collectabomasaldigesta,feces,suppliedfeed,andortsamples;1daytocollectruminalﬂuidat0,2,4,and6hafterthe

morningmeal;and1dayforurinespotsample,obtainedbymassageoftheexternalgenitaliaofthesteers.Bloodcollection

wasmadebyjugularveinpuncture4hafterthemorningfeeding.Ortswereremovedforeachanimaleachdaybeforethe

morningmealandwereweighed,sampled,placedinsideplasticbags,andfrozenat−18◦_C._The_supplied_feed_was_sampled

threetimeseachweekandwasalsoplacedinsideplasticbagsandfrozenat−18◦_C.

Table2

Chemicalcompositionsofcornsilageandconcentratesofeachtreatment(g/kgDM).

Itemsb _Corn_silage _Replacement_levels_(IDY_replacing_SBM_g/kg)a

0 250 500 750 1000 DM 313.4 884.9 885.6 888.1 890.2 893.8 OM 966.0 956.4 958.3 945.8 956.3 952.4 CP 74.4 226.4 221.0 228.9 228.9 223.3 NDIN 93.7 118.3 117.4 118.7 113.0 73.2 ADIN 48.0 15.1 14.7 16.9 11.2 8.3 EE 22.6 30.9 28.3 26.4 24.8 20.0 NFC 316.8 524.9 517.6 509.7 540.0 609.2 NDF 567.6 221.6 233.8 261.5 248.7 183.8 aNDFom(n) 552.2 191.2 210.9 235.0 222.9 166.7 iNDF 214.0 20.8 20.9 18.1 19.0 14.7 ADF 302.1 35.5 30.8 28.0 21.7 13.4 HEM 265.5 186.1 203.0 233.5 227.0 170.4 CEL 257.3 30.3 23.2 19.5 16.8 10.1 LIG 42.8 4.2 6.3 7.2 3.7 2.7

a_{IDY–inactive}_dry_yeast;_{SBM–soybean;}

b _DM:_dry_matter,_OM:_organic_matter,_CP:_crude_protein,_NDIN:_neutral_detergent_insoluble_nitrogen_(g/kg_N),_ADIN:_acid_detergent_insoluble_nitrogen

(g/kgN),EE:etherextract,NFC:non-fibrouscarbohydrates,NDF:neutraldetergentfiber,aNDFom(n):neutraldetergentfibreassayedwithaheatstable amylaseandcorrectedforashandnitrogenouscompounds,iNDF:indigestibleNDF,ADF:aciddetergentfiber,HEM:hemicellulose,CEL:celluloseandLIG: lignin.

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Chromiumoxide(Cr2O3)wasusedtodeterminethefecalexcretionandabomasumﬂowofnutrients,andwas

adminis-teredinasingledaily15gdoseat11h00viarumenﬁstulaonthefourthdayofeachexperimentalperiod.Dailycollections

of500mLofabomasaldigestaand200goffeceswereperformedevery22hbetweenthe11thand16thdayofeach

experi-mentalperiod.Feedsamples,orts,feces,andabomasaldigestawereplacedinlabeledplasticbagsandstoredat−18◦_C_for

lateranalysis.

RuminalﬂuidwascollectedtomeasurethepHandammonianitrogen(N NH3)concentrations,andthesesampleswere

collectedat0,2,4,and6hafterthemorningfeedingonthe17thexperimentaldayofeachperiod.ThepHwasimmediately

measuredaftercollection;1mLof1:1sulfuricacid(H2SO4)wasaddedtothesample,whichwasthenstoredinthefreezer

at−18◦_C_for_later_ruminal_N _NH₃_{concentration}_analysis.

Fourhoursafterthedietwasconsumedonthe18thdayofeachexperimentalperiod,bloodwascollectedbyjugular

veinpunctureinatesttubecontainingaseparationgelwithacoagulantactivator(SSTIIAdvance,BDVacutainer,SãoPaulo

city,SãoPaulostate,Brazil).Thesesampleswerestoredat−15◦_C_for_later_urea_analyses._{Concomitantly,}₅₀_mL_urine_spot

sampleswereobtainedforeachanimal.Theurinewasﬁltered,and10mLaliquotswereremovedandimmediatelydiluted

in40mLof0.036NH2SO4topreventbacterialdestructionofthepurinederivatives(PD)anduricacidprecipitation.These

sampleswerestoredat₋₁₅◦Cforlateranalysisofurea,creatinine,allantoin,anduricacid.Anundilutedurinesamplewas

storedfordeterminingthetotalnitrogencompoundyields.

Attheendofeachexperimentalperiod,thefeedsamples,orts,feces,andabomasaldigestawerethawedandsubjectedto

pre-dryingat60◦Cfor72handwerethengroundinaWiley-typeknifemill(TE-625,TECNAL,Piracicaba,SãoPaulo,Brazil)

witha1mmmesh.Compositesamplesweresavedforeachanimalonadryweightbasisfromeachtimeperiod.

2.4. Chemicalanalysis

DM,organicmatter(OM),andcrudeprotein(CP)analyseswereperformedaccordingtotheAOAC(1990),methodnumber

934.01forDM,930.05forOM,and981.10forCP.Etherextract(EE)wasanalyzedbySoxhletextractionwithpetroleum

ether,accordingtotheAOAC(1990),methodnumber920.39.Theconcentrationofneutraldetergentﬁberwasassayedwith

aheat-stableamylaseandcorrectedforashandnitrogenouscompounds[aNDFom(n)]byusingtechniquesdescribedby

Mertens(2002),withcorrectionsforproteinaccordingtoLicitraetal.(1996)andaddedthermostablealpha-amylase(Ankon

Tech.Corp.,Fairport,NY,USA).Lignin(sa)wasextractedwithsulfuricacid720mL/L(VanSoestandWine,1967).Neutral

detergentinsolublenitrogen(NDIN)and aciddetergentinsolublenitrogen(ADIN)(Licitraetal.,1996)weremeasured

usingtheKjeldahlmethod.Non-ﬁbrouscarbohydrates(NFC) werecalculated asfollowsaccordingtoHall(2000): NFC

(g/kg)=1000−[(CP–ureaderivedCP+urea)+NDFap+EE+ash],where:CP=crudeprotein;NDFap=neutraldetergentﬁber

correctedforashandprotein;andEE=etherextract.

ThechromiumoxidecontentoffecesandabomasaldigestawasdeterminedaccordingtoWilliamsetal.(1962),withan

atomicabsorptionspectrophotometer.Theﬂowoffecaldrymatter(FDM)andabomasaldrymatter(ADM)wascalculated

asfollows:

FDMorADM

_kg

day

= _fecal_or_abomasalingested_markermarker (g)_{concentration}×100

ThecoefﬁcientsofruminalandintestinalapparentdigestibilityofDM,OM,NDFap,andNFCwerecalculatedinrelation

tothetotaldigestibleDM,whereastheruminalandintestinaldigestibilityofCPandEEwascalculatedinrelationtothe

amountsthatarrivedateachstudysite.

Theammonianitrogenconcentrationofruminalﬂuid sampleswasdeterminedbyusingthecolorimetrictechnique

describedbyChaneyandMarbach(1962).Creatinineanalysiswasperformedwithacidpicrateusingacommercialkit

(LabtestDiagnóstica,UréiaCE,LagoaSanta,MinasGerais,Brazil),accordingtothemodiﬁeddiacetylmethod.Dailycreatinine

excretionwasestimatedbasedonthe27.76mg/kgBWrecommendations(Rennóetal.,2000).Dailyurinevolumewas

estimatedbydividingdailycreatinineexcretionbyitsconcentrationintheurinespotsample.Thedeterminationofureain

urinewasperformedwithanenzymaticcolorimetricmethodusingacommercialkit(LabtestDiagnóstica,UreaCE,Lagoa

Santa,MinasGerais,Brazil).TheNBwascalculateding/dayasfollows:Nintake–(fecalN+urineN).

AnalysesofPD,allantoin,anduricacidwereperformedusingacolorimetricmethodbyFujiharaetal.(1987),whichwas

describedbyChenandGomes(1992).PDexcretionwascalculatedbymultiplyingtheurinevolume,whichwasestimated

within24h,bythePDconcentrationofthespoturinesamples.Absorbedpurines(Y,mmol/day)werecalculatedfromthe

PDexcretion(X,mmol/day)byusingtheequationY=0.85X+0.385LW0.75_,_in_which_0.85_is_the_recovery_of_absorbed_purines

asPDand0.385LW0.75_is_the_endogenous_contribution_to_purine_excretion₍_Verbic_et_al.,₁₉₉₀_)._The_production_of_microbial

nitrogencompounds(Nmic)wascalculatedas:

Nmic

_gN day

= 70×absorbedPD 0.93×100×0.137

where70istheNcontentofpurines(mgN/mmol),0.93representsthetruedigestibilityofpurines,and0.137istheaverage

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Table3

Averagedailyintakeofdrymatter(DM)andnutrientandproductiveperformanceofgrowingbeefcattlefedwithinactivedryyeast(IDY)inconcentrate (EXP1).

Itemsa _Replacement_levels_(g/kg) _Effect_(P-value)

0 250 500 750 1000 SEM Linear Quadratic

DM,kg/d 9.6 9.5 9.4 9.2 8.4 0.14 0.003 0.110 CP,kg/d 1.3 1.2 1.2 1.1 0.9 0.03 <0.001 0.308 aNDFom(n),kg/d 3.5 3.6 3.5 3.9 3.8 0.06 0.043 0.795 DM,gDM/kgBW 21.4 21.1 21.4 20.9 19.2 0.02 0.004 0.065 aNDFom(n),gDM/kgBW 8.0 8.1 8.1 9.0 8.9 0.02 0.011 0.694 ADG,kg/d 1.3 1.3 1.3 1.2 1.1 0.04 0.028 0.531 CADG,kg/d 0.9 0.9 1.0 0.9 0.9 0.02 0.709 0.144 Dressing,g/kg 558 567 572 556 562 2.7 0.904 0.219

FE,ggain/kgDMI 141 139 130 128 128 0.25 0.282 0.687

a_DM:_dry_matter;_CP:_crude_protein;_aNDFom(n):_neutral_detergent_ﬁbre_assayed_with_a_heat_stable_amylase_and_corrected_for_ash_and_nitrogenous

compounds;ADG:averagedailygain;CADG:carcassaveragedailygain;CY:carcassyield(%);FE:feedefﬁciency.

2.5. Statisticalanalyses

ThenutrientintakeandanimalperformanceanalysesinEXP1weresubjectedtoanalysesofvarianceinacompletely

randomizeddesignwithﬁvetreatments,namely,0,250,500,750,and1000g/kgsoybeanmealreplacementwithIDYand

sevenreplicates.TheinitialBWofsteerswasconsideredtobeacovariateinthestatisticalmodel,whichemployedthePROC

MIXEDoptioninSASsoftware(version9.1),accordingtothefollowingmodel:

Yi=+Ti+ˇ(Xi− ¯X)+ei

where:Yi=dependentvariablecorrespondingtoexperimentalobservations;=generalmean;Ti=ﬁxedeffectoftreatments

i;ˇ=regressioncoefﬁcientorfunctionalrelationshipwithcovariate;Xi=observedvalueofcovariateappliedtoexperimental

unit; ¯x=meanvalueforcovariate;andei=randomerrorassumingnormalindependentdistribution(NID)(0;␴2␧).

InEXP2,whichassessedtotalandpartialdigestibility,nitrogenefﬁciency,andruminalpHandammonianitrogen,the

analyseswereconductedina5×5LatinsquaredesignwiththePROCMIXEDoptioninSASsoftware(version9.1),according

tothefollowingmodel:

Yijk=+Ti+Aj+Pk+eijk

whereYijk=dependentvariablemeasuredinanimaljthatwassubjectedtotheitreatmentinperiodk;=generalmean,

Ti=ﬁxedeffectoftreatment,Aj=randomeffectofanimalj,Pk=randomeffectofperiodk,andeijk=randomerrorassuming

NID(0;␴2␧).

Inthiscase,theﬁxedeffectwasrepresentedbysoybeanmealreplacementlevelsbyIDYandtherandomeffectswere

representedbyanimalandperiodeffects.TheﬁxedeffectsforevaluatingruminalpHandammonianitrogeninthe5×5

LatinsquarewerethereplacementlevelofsoybeanmealbyIDY,collectiontime(T),andtheinteractionbetweenthese

twofactors(Y×T).Periodandanimalwereconsideredtoberandomeffectswithinthemodel.Aschemeofrepeatedtime

measurementswasused(Littelletal.,1998),withcollectiontimes(0,2,4,and6hafterfeeding)repeatedoncewithineach

experimentalunit(animal×period).

Replacementlevelcomparisonsfollowedthedecompositionoforthogonalpolynomialsinlinear,quadratic,cubic,and

quarticeffectsandwereconductedusingPROCMIXEDinSASsoftware(version9.1).Homogeneityofvariancesbetween

treatmentswasassumedandthedegreesoffreedomwereestimatedbyusingtheKenward–Rogermethod.Theregression

modelswereadjustedaccordingtothesigniﬁcanceofthe␤1,␤2,␤3,and␤4parametersbyusingarestrictedmaximum

likelihoodmethodinPROCMIXED,andtheparameterestimateswereobtainedthroughPROCREGinSASsoftware(version

9.1).Thesameprocedurewasperformedtoobtainthelinear,quadratic,andcubiceffectsofcollectiontimesontheruminal

pHandammonianitrogendata.Allstatisticalprocedureswereconductedbyusing0.05asthecriticalprobabilitylevelfor

atypeIerror.

3. Results

3.1. Nutrientintake(EXP1)

TheintakeofDM(P=0.003)andCP(P<0.001)inkg/dayandDMing/kgBWdecreased(P=0.004)linearlyasthedietary

IDYincreased(Table3).Conversely,theaverageintakeofNDFaping/day(P=0.043)andg/kgBWincreased(P=0.011)as

IDYwasaddedtotheconcentrate.TheintakeofNFCandtotaldigestiblenutrients(TDN)showednodifference(P>0.05)

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Table4

Averagetotal,ruminalandintestinalapparentdigestibilitiesingrowingbeefcattlefedwithinactivedryyeast(IDY)inconcentrate(EXP2).

Itemsa _Replacement_levels_(g/kg)b _Effect_(P-value)

Totalapparentdigestibility(g/kg)c

DM 620.9 671.1 647.1 658.9 660.1 12.6 0.731 0.766 OM 640.3 691.5 670.8 681.7 685.9 12.2 0.652 0.762 CP 622.0 632.3 605.0 611.3 612.6 15.3 0.998 0.876 EE 736.8 726.0 734.3 731.1 698.5 20.3 0.949 0.919 aNDFom(n) 593.3 620.6 552.7 636.0 602.9 16.5 0.745 0.760 NFC 745.4 764.5 794.2 716.8 776.8 10.8 0.933 0.907

Ruminalapparentdigestibility(g/kg)d

Intestinalapparentdigestibility(g/kg)e

a_DM:_dry_matter,_OM:_organic_matter,_CP:_crude_protein,_EE:_ether_extract,_NFC:_non-ﬁbrous_{carbohydrates,}_aNDFom(n):_neutral_detergent_ﬁbre_assayed

withaheatstableamylaseandcorrectedforashandnitrogenouscompounds.

b_Five_experimental_units_per_treatment_(Latin_square₅_×_5).

c_Total_apparent_{digestibility}_(g/kg)₌_[(Nutrient_intake₋_Nutrient_{excretion)/Nutrient}_intake]_×_1000. d_Ruminal_apparent_{digestibility}_(g/kg)₌_[(Nutrient_intake₋_Nutrient_abomasal_{ﬂow)/Nutrient}_intake]_×_1000.

e_Intestinal_apparent_{digestibility}_(g/kg)₌_[(Nutrient_abomasal_ﬂow₋_Nutrient_{excretion)/Nutrient}_abomasal_ﬂow]_×_1000.

3.2. Animalperformance(EXP1)

IDYlevelshadnoeffect(P>0.05)onproductiveperformancevariables,withtheexceptionoftheADG,whichlinearly

decreased(P=0.028)asIDYwasaddedtotheconcentrate(Table3).Theﬁttedequationforthisvariablewasasfollows:

ADG=1.39451−0.00269X(r2₌_0.1490).

3.3. Digestibility,ruminalpH,andammoniaconcentration(EXP2)

Theexperimentaldietshadnoeffect(P>0.05)onthetotalandpartialapparentdigestibilityofnutrients(Table4).No

effectswerefoundfortheIDYlevel(P>0.05)ortheinteractionbetweenIDYlevelandcollectiontimeafterfeeding(P>0.05)

onN NH3andpH(Table5).Conversely,collectiontimeafterfeedinghadlinear(P<0.001)andquadraticeffects(P<0.001)

onpHandN NH3 variables,respectively(Table5).pHshowedadecreasinglineartrend(pH6.15576−0.11732X)from

time-point0(pH6.18)until6hafterfeeding(pH5.47).N NH3exhibitedquadraticbehaviorasafunctionofcollectiontime

Table5

AveragesforpH,ruminalN-ammonia(N NH3,mg/dL)andefﬁciencyofnitrogenusageingrowingbeefcattlefedwithinactivedryyeast(IDY)inconcentrate

(EXP2).

Itemsa _Replacement_levels_(g/kg)b _Effect_(P-value)

pHc _5.80 _5.72 _5.66 _5.97 _5.85 _0.15 _0.192 _0.352 N NH3mg/dLd 12.94 12.41 12.89 12.16 11.14 0.68 0.144 0.848 PUN,mg/dL 14.23 15.82 17.16 14.20 15.94 0.61 0.749 0.965 UUN,g/d 48.27 43.72 47.42 41.64 47.90 0.74 0.239 0.064 Nmic,g/d 91.37 81.96 87.78 82.66 84.36 1.58 0.064 0.308 Emic,gCP/kgTDN 138.43 122.26 157.15 154.05 166.42 8.85 0.572 0.293 NB,g/d 30.74 23.69 20.54 24.60 26.63 0.78 0.339 0.747

a_Plasma_urea_nitrogen_(PUN)._Urinary_urea_nitrogen_(UUN)._Microbial_nitrogen_(N

mic).Microbialefﬁciency(Emic)andnitrogenbalance(NB). b_Five_experimental_units_per_treatment_(Latin_square₅_×_5).

c_Main_effects_relative_to_pH:_replacement_level_(L)_P₌_0.342,_collection_time_(T)_P_<_0.001_and_L_×_T₌_0.147. d_Main_effects_relative_to_NNH3:_replacement_level_(L)_P₌_0.391,_collection_time_(T)_P_<_0.001_and_L_×_T₌_0.944.

Slicingtheeffectrelativetocollectiontime(T)forpH,pH:linear(P<0.001)quadratic(P=0.1053)andcubic(P=0.9612).Effectsrelativetocollectiontime (T)forN NH3:linear(P<0.001)quadratic(P<0.001)andcubic(P=0.5290).

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(Table5).BycalculatingthederivativeofequationN NH3=7.54381+2.72635X−0.25516X2,thepeakwasobtainedat5.3h

withanexpectedmaximumresponseof14.82mgofN NH3perdLofruminalﬂuid.

3.4. Nitrogenuseefﬁciency(EXP2)

NoeffectofIDY(P>0.05)onvariablesrelatedtodietarynitrogenefﬁciencywasfound(Table5).Aquarticeffectwas

foundforurinaryureanitrogen(UUN);however,thiseffectwasnotrelevantbecauseofitslackofbiologicalsigniﬁcance.

4. Discussion

4.1. Nitrogenintake(EXP1)

AlineardecreaseinDMintakewithincreasingreplacementlevelsofsoybeanmealbyIDYcanbeexplainedbythevery

ﬁnetextureoftheyeast,whichmostlikelyhinderedfeedintakebythesteers,asnotedintheexperimentalphase,making

theconcentratewithhighyeastlevelsmorestickyrelativetotheconcentratecontainingonlysoybeanmeal.Tegbeand

Zimmerman(1977)alsofoundthatincludingIDYinthedietmodiﬁedthetextureofpigfeed,givingastickyconsistencyin

thepigs’mouthsandhinderingingestion.Pradoetal.(2000)assessedDMintakeinﬁnishingheifersthatreceiveddietsin

whichcottonseedmealwasreplacedbyIDY,andtheyalsofoundareductioninDMintakewithanincreaseinIDYlevels.

LineardecreasesalsooccurredinOMandCPintakes.TheseresultsaremostlikelyduetotheDMintakeandalsotothe

experimentaldietcomposition(Table2),whichdisplayedlowerconcentrationsoftrueCPandEEwithincreasedamounts

ofIDYintheconcentrate.TheinclusionofyeastdecreasedtheproportionoftrueCPbecauseofthelowerconcentrationof

yeastrelativetosoybeanmeal.Itisworthnotingthattheinclusionofahigherproportionofurea(Table1)indietswith

higherIDYlevelswasusedtoformulateisoproteicdiets.Theincreasinglevels(109,126,141,157,and174g/kgDM)of

urea+ammoniumsulphate(9:1)wereusedtomakeupthetotalproteincontent.However,thehighernon-proteinnitrogen

(NPN)andtrueproteinratiointhedietswithhigherIDYinclusionlevelsseemtohavesigniﬁcantlycontributedtoareduction

intheintakeofDMandCP.Ureacouldprobablydepressintakebyreducingthepalatabilityofthedietswithhigherinclusion

levelsofIDYandurea.

TheNDFapintakeincreasedwithanincreaseofIDYinthediet.ThereductionofDMintakeatthehighestIDYlevelsmost

likelyoccurredthroughaselectivereductioninconcentrateintake.Thelikelymaintenanceofforageintakewithareduction

inconcentrateacceptabilitycouldexplainthelinearincreaseinNDFapintake,throughasimpledilutioneffect.TheNFC

intakeremainedunchangedduetoagreaterNFCcontentintheconcentrates(Table2),whichresultedinalowerintakefor

greaterIDYinclusionlevels.

AlthoughincreasedIDYlevelsaffectedtheintakeofalmostallnutrients(Table3),thisincreasedidnotresultindifferences

inapparentdigestibilitycoefﬁcients.AccordingtoVanSoest(1994),thedigestibilityoffeedsisdirectlyinﬂuencedbyfactors

suchasingestionandfeedcomposition,feedprocessing,theprotein:energyratio,degradabilityrate,andinherentanimal

factors.ItisknownthatNDFexertsasigniﬁcanteffectonintakeregulationandisresponsibleforthephysicallimitationof

dietaryintake.However,whendietaryNDFisbelow500–600g/kgDM,theintakeisnothighlycorrelatedwithdigestibility

(Mertens,1994)whichmayhaveoccurredinthepresentexperiment.

4.2. Animalperformance(EXP1)

AnimalperformanceparameterssuchasmeatandmilkproductionaredirectfunctionsofDMintake,asaconsequence

ofagreaterorlessersupplyofnutrients(Mertens,1994).ThelineardecreaseinADGwithincreasedIDYinthedietsdirectly

reﬂectstheeffectfoundforDMintake.However,alineardecreaseinDMintakeshowednoeffectontheaveragecarcass

gain,carcassyield,orfeedconversion.

TheCADGisaneconomicallyimportantvariableforproducersofbeefcattlebecausetheproducer’scompensationbythe

packingplantisbasedontheHCW.Thecarcassyieldandfeedconversionalsoshowednodifferencesbetweentreatments.

Therefore,onecaninferthatyeastcanpotentiallyreplacesoybeanmealinthedietsofﬁnishingNelorecattle,althoughthis

replacementisconditionedbyeconomicfactors.

4.3. Digestibility,ruminalpH,andammoniaconcentration(EXP2)

Averageruminaldigestibilityvaluesof567.0and628.7(g/kg)werefoundforDMandOM,respectively.Theruminal

digestibilityofOMwasclosetotheaveragevalueof650g/kgthatwasfoundbytheBritishAgriculturalResearchCouncil

(ARC)(ARC,1984)fordifferentfeeds.AlthoughyeastisasourceofRDP,nodifferenceintheruminaldigestibilityofthis

nutrientwasobserved,which canbeexplainedbyitslow intakebytheanimals,possiblypreventinggreaterlevelsof

degradation.TheaveragerumenCPdigestibilityof43.5g/kgindicatesthatﬂuidlossesofnitrogencomponentsintherumen

werelowandthatnitrogensourceswereusedtoagreaterextentbymicroorganisms.

Fregadollietal.(2001)foundthatruminalandintestinaldigestibilitywerenotaffectedbytheinclusionofahighly

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digestibilityofDMandOM,respectively.AsforCP,anegativevaluewasfoundforruminaldigestibility,withanaveragevalue

of_−185.0g/kg;thoseauthorsattributedthisvaluetotheendogenousNrecyclinginanimalrumensaswellastomicrobial

proteinsynthesis.

Anaveragevalueof830g/kgforNDFapruminaldigestibilityiswithintherangecommonlyfoundintheliterature;for

example,Chizzottietal.(2005)observedanaveragevalueof890g/kgindietsexhibitingaforage:concentrateratioof60:40.

ThedigestibilityofNDFapintheintestineshadanaveragevalueof179.3%,whichwasexpectedbecauseNDFapdigestibility

isusuallylow.Messanaetal.(2009)alsofoundthatyeasthadeffectontotalandruminalnutrientdigestibilitycoefﬁcients

inNelorecattledietscontainingcottonseedprocessingby-productsasforage.

Anaveragevalueof12.31mg/dLNH3 Ninruminalﬂuid(Table5)wasfoundinthisstudyforthedifferenttreatments,a

valuethatisabovetheminimumconcentrationof5mg/dLrecommendedbySatterandSlyter(1974)asanadequatevalue

forsatisfactoryinvitromicrobialgrowth.Hoover(1986)proposedvaluesof3.3and8.0mgNH3 Nforthemaximization

ofmicrobialgrowthandOMdigestionintherumen,respectively.Mehrezetal.(1977)foundthattheminimumammonia

concentrationformaximummicrobialgrowthshouldbe23mg/dL.Conversely,LengandNolan(1984)foundthat

concen-trationsabove5–10mg/dLofruminalﬂuiddidnotleadtoanincreaseinmicrobialproteinproduction.Sampaioetal.(2009)

andLazzarinietal.(2009)assessedtheeffectsofnitrogensupplementationinanimalsfedwithlow-qualityforageandfound

ruminalammoniaconcentrationvaluesof9.64and15.33mg/dL,respectively;thesevaluesmaximizedthevoluntaryfeed

intakeoftheanimalsandconsequentlyaffectedtheirperformance.

ThepHdecreasedlinearlywithrumenﬂuidcollectiontime(Table5),withestimatedvaluesof6.15and5.45at

time-points0and6hafterfeeding,respectively.pHvaluesbelow6.2caninhibitdigestionrateandincreasethelagtimeforcell

walldegradation(VanSoest,1994).However,Hoover(1986)proposedthatonlypHvaluesbelow5.0–5.5couldinhibitthe

developmentofcellulolyticmicroorganisms.Nevertheless,theruminaldigestibilityofNDFapwasnotaffectedbyincreasing

levelsofyeast(Table4),indicatingthattherewaslikelysatisfactorygrowthofcellulolyticmicroorganismsandthatthese

lowpHvaluesseemedtonotaffectﬁberdegradationinanyofthedietsunderstudy.

4.4. Nitrogenuseefﬁciency(EXP2)

UreaistheprimaryformofNexcretioninmammals.Theureaconcentrationofbloodplasmaiswellestablishedasa

parameterforassessingdietaryCPuseinefﬁciency.Thepresenceofhighproportionsofnitrogeninbodyﬂuidindicates

that,intherumenatleast,thereislowammoniautilizationandthatitisbeingabsorbedbytheepitheliumoftheorgan

(BroderickandClayton,1997).Thisstudy’saverageplasmaureanitrogen(PUN)concentrationof15.55mg/dLiswithinthe

normallimitsforcattle.UreaisonemetaboliteofdietaryproteinthatisformedfromdetoxiﬁcationofNH4bytheliver.

Levelsofureaintheplasmaorserum(PUNorSUN)arereﬂectiveofthequantityanddegradabilityoftheproteinconsumed,

oftheseverityofnegativeenergybalanceinfastedanimals,orofthecombinationofproteinfeedingandnegativeenergy

balance.PUNconcentrationshaveoftenbeenusedasacorrelatefordietaryproteinlevelandfertility(ElrodandButler,1993).

Fergusonetal.(1991)havesuggestedthatwhenSUNconcentrationsare>20mg/dL,fertilitywillbeimpaired.Althoughan

effectofdifferentdietsonCPintakeandruminalammoniaconcentrationwasdetected,andthesetwoparametersarethe

mainfactorsthatinﬂuencetheamountofnitrogenpresentinbodyﬂuids,thePUNconcentrationwasnotaltered.

Whenthesynthesisrateofammoniaexceedsitsutilizationbymicroorganisms,anincreaseinruminalammonia

con-centrationoccurs,withaconsequentincreaseinurinaryureaexcretion(Russelletal.,1992).ThelowerCPintakethatwas

recordedinanimalsreceivinghigherIDYlevelsseemstohavebeencompensatedforbyanumericallygreatereffectonEmic

intheseanimals,whichwasreﬂectedinthesimilarconcentrationsofruminalPUN,UUN,andNH3 Nforanimalsinthe

differenttreatmentgroups.Anaveragevalueof157.1gCP/kgTDNwasestimatedforEmicinthepresentstudy,whichis

greaterthanthevalueof120gCP/kgTDNthatwasestablishedasareferencefortropicalconditionsbyValadaresFilhoetal.

(2010)andisalsogreaterthanthevalueof130gCP/kgTDNreportedbytheUSNRC(2001).

5. Conclusions

ThereplacementofsoybeanmealbyIDYinfeedconcentratehasemergedasafeasiblealternativeforbeefcattleproducers.

However,itsuseshouldbeconditionalonproductavailabilityandprice.AlthoughincreasedlevelsofIDYintheconcentrate

resultedinreducedintakeandADG,IDYallowedsatisfactoryfeedconversionandcarcassgain.IDYalteredDMintakein

beefcattleinthefeedlotaswellasADG,withoutaffectingtheapparentdigestibilityofnutrientsormicrobialefﬁciency.

Acknowledgements

The authorswish tothanktheConselho Nacionalde PesquisaeDesenvolvimento Cientíﬁco eTecnológico (CNPq),

Fundac¸ãodeAmparoàPesquisadoEstadodeMinasGerais(FAPEMIG),and InstitutoNacionaldeCiênciaeTecnologia

CiênciaAnimal(INCT-CA)forﬁnancialsupport.

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