ContentslistsavailableatScienceDirect
Animal
Feed
Science
and
Technology
journalhomepage:www.elsevier.com/locate/anifeedsci
Short
communication
Effects
of
crude
glycerin
on
milk
composition,
nutrient
digestibility
and
ruminal
fermentation
of
dairy
cows
fed
corn
silage-based
diets
P.G.
Paiva
a,∗,
T.A.Del
Valle
b,
E.F.
Jesus
a,
V.P.
Bettero
a,
G.F
Almeida
b,
I.C.S.
Bueno
c,
B.J.
Bradford
d,
F.P.
Rennó
b,∗∗aDepartmentofAnimalScience,UNESP—UniversidadeEstadualPaulista“JúliodeMesquitaFilho”/CampusJaboticabal,Rod.Prof.Paulo
DonatoCastellanekm5,Rural,14884-900Jaboticabal,SP,Brazil
bDepartmentofAnimalNutritionandProduction,SchoolofVeterinaryMedicineandAnimalScience,UniversityofSaoPaulo(USP),Av.
DuquedeCaxiasNorte,225-CampusdaUSP,13635-900,Pirassununga,SP,Brazil
cDepartmentofAnimalScience,CollegeofAnimalScienceandFoodEngineering,UniversityofSaoPaulo,Pirassununga,SP,Brazil
dDepartmentofAnimalSciencesandIndustry,KansasStateUniversity,66506Manhattan,USA
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received2May2015 Receivedinrevisedform 18December2015 Accepted21December2015 Keywords: Biofuels By-product Fiberdigestibility Glycerol Milkcomposition
a
b
s
t
r
a
c
t
Theobjectiveofthecurrentstudywastoevaluatetheeffectsofincreasinglevelsofcrude glycerinondrymatterintake,nutrientdigestibility,ruminalparameters,blood metabo-lites,milkyieldandcompositionofdairycowsfedcornsilage-baseddiets.Twenty-four Holsteincows(16non-cannulatedand8rumen-cannulated;184±50daysinmilk[DIM] and594±39kgofbodyweight[BW])wereassignedtoareplicated4×4Latinsquaredesign experiment,consistingof14daysforadaptationtodietsand7daysforsampling.Cowswere assignedtoreceiveoneofthediets:0(Control),70,140or210gofcrudeglycerin/kgof dietdrymatter(DM).Drymatterintakeandmilkyieldlinearlydecreasedwiththe inclu-sionofcrudeglycerin.However,crudeglycerindidnotaffectmilkcomposition.Total-tract digestibilityofDM,crudeprotein(CP)andetherextract(EE)linearlyincreased,and neu-traldetergentfiber(NDF)digestibilitylinearlydecreasedaccordingtodietaryinclusionof crudeglycerin.Feedingcrudeglycerinchangedvolatilefattyacidconcentrations:linearly increasedpropionate,quadraticallyaffectedbutyrate,andlinearlydecreasedacetate con-centrations,resultinginloweracetatetopropionateratio.Totalvolatilefattyacidwasnot affectedbycrudeglycerin.RuminalNH3-Nlinearlydecreasedaccordingtocrudeglycerin
dietarylevels.Crudeglycerinlinearlyincreasedbloodglucoseconcentration.Inclusionof highlevelsofcrudeglycerin(210g/kg)indietsofmid-lactatingcows,increaseddry mat-terdigestibilityandruminalpropionateconcentrations,butnegativelyaffecteddrymatter intakeandmilkyield.
©2015ElsevierB.V.Allrightsreserved.
Abbreviations: BCFA,branchedchainfattyacids;BUN,bloodureanitrogen;BW,bodyweight;CP,crudeprotein;DIM,daysinmilk;DMI,drymatter
intake;EE,etherextract;aNDF,neutraldetergentfiberwithresidualash;NFC,non-fibercarbohydrate;VFA,volatilefattyacids.
∗ Correspondingauthor.Fax:+551935654368.
∗∗ Correspondingauthor.
E-mailaddresses:bocazoo@hotmail.com,pagppaiva@gmail.com(P.G.Paiva),francisco.renno@usp.br(F.P.Rennó).
http://dx.doi.org/10.1016/j.anifeedsci.2015.12.016
1. Introduction
Thegrowthofthebiofuelindustryhasincreasedthedemandforcorn,affectingpricesandthelivestocksector(USDA, 2014).Therefore,newalternativefeedsourcesarerequiredinordertoreduceanimalfeedcosts.Crudeglycerinisa by-productobtainedfromoilprocessinginthebiodieselindustry,whereinforeachliterofbiodieselproduced,0.1lofcrude glycerinisformed(Dasarietal.,2005).Crudeglycerincontains800–880gofglycerol/kg(Donkin,2008)andglycerolor purifiedglycerin(>95%glycerol)hasbeenusedtopreventmetabolicproblemsintransitioncows(GoffandHorst,2003; PiantoniandAllen,2015).
Crudeglycerincanbeconvertedintovolatilefattyacid(VFA)inrumen,mainlyintopropionate(Wangetal.,2009),orcan beabsorbedthroughtherumenepitheliumandoxidizedintheliver,increasingtheenergyavailableforanimalutilization (Remondetal.,1993).Severalstudieshavereportedthatreplacingcornwithglycerinincreasedtheruminalmolarproportion ofpropionate(DeFrainetal.,2004;Shinetal.,2015;Boydetal.,2013).
Thereisalackofdataexaminingcrudeglycerinasaprimaryenergysourceingredientinrationsofdairycows,mainly indietarylevelshigherthan100g/kg(drymatter[DM]basis).Thus,theobjectiveofthepresentstudywastoevaluatethe effectsofincreasingdietarylevelsofcrudeglycerin(upto210g/kgdietDM)ondrymatterintake(DMI),nutrientdigestibility, ruminalparameters,bloodmetabolites,milkyieldandcompositionoflactatingdairycowsfedcornsilage-baseddiets.Our hypothesiswasthatcowsfedcrudeglycerincouldmaintainmilkyieldandcompositionwithoutimpairingDMIandnutrient digestibility.
2. Materialsandmethods
ExperimentalprocedureswereapprovedbytheEthicsCommitteeoftheSchoolofVeterinaryMedicineandAnimal ScienceoftheUniversityofSãoPaulo(approvalnumber3058/2013).
2.1. Animals,dietsandexperimentaldesign
Twenty-fourmultiparousHolsteincows(184±50daysinmilk[DIM]and594±39kgbodyweight[BW],mean±SD),16 non-cannulatedand8rumencannulated,wereassignedtoareplicated4×4Latinsquaredesignexperimentwith21day periods(14dayofadaptationand7dayofsampling).Thecowsweregroupedaccordingtomilkyieldandthenassignedto eachsquareaccordingtoBW,exceptfor2squaresthatwereformedbytherumencannulatedcows.Thus,24repetitionsper treatmentwereusedforstatisticalanalysis.Theanimalswereassignedwithineachsquaretoreceiveoneofthefollowing diets:0(Control),70,140or210gofcrudeglycerin/kgofdietDM.DietswereformulatedaccordingtoNRC(2001),and ingredientsandchemicalcompositionaredescribedinTable1.Thecrudeglycerincontained806g/kgofglycerol,63g/kg ofashand124.6g/kgofwater,andwasobtainedfromsoybeanoil(ADM,Rondonopolis,Brazil).Thecrudeglycerinwas mixedintotheconcentratebeforethemorningfeeding.Cowswereindividuallyfedtwicedaily(50%oftotaldietDMin eachfeeding)at0700and1300htosupply105–110%ofexpectedfeedintake(onasfed-basis).Thefeedwasindividually Table1
Ingredientsandchemicalcompositionofexperimentaldiets.
Item,g/kgofdietDM Glycerininclusion,g/kgofDM
0 70 140 210 Cornsilagea 501.4 500.3 505.9 504.0 Groundcorn 300.5 219.2 125.1 45.0 Soybeanmeal 162.1 174.6 192.8 204.8 Crudeglycerinb 0.0 69.9 140.2 210.2 Mineralpremixc 29.8 29.8 29.8 29.8 Urea 5.30 5.30 5.30 5.30 Ammoniumsulphate 0.90 0.90 0.90 0.90 Composition Drymatter 586.4 587.6 585.0 586.6
Neutraldetergentfiber 301.1 290.5 281.9 271.0
Nonfibercarbohydrated 455.7 464.1 468.1 468.1
Crudeprotein 162.3 160.7 161.2 159.5
Etherextract 31.1 31.2 31.0 31.2
Ash 66.3 70.1 74.3 78.0
Netenergye(Mcal/kgDM) 1.74 1.75 1.75 1.75
aComposition:293.0ofdrymatter(DM);70.5ofcrudeprotein(CP);556.7ofneutraldetergentfiber(NDF);29.7ofetherextract(EE)and38.6ofash. bComposition:806g/kgofglycerol,63g/kgofashand124.6g/kgofwater,obtainedfromsoybeanoil(ADM,Rondonopolis,Brazil).
cContainedperkg:88.0gofCa;42.0gofP;18.0gofS;45.0gofMg;123.0gofNa;14.0mgofCo;500.0mgofCu;20.0mgofCr;1050.0mgofFe;28.0mg
ofI;1400.0mgofMn;18.0mgofSe;2800.0mgdeZn;80.0mgofBiotin;200.000,00UIvitaminA;40.000,00UIvitaminD;1.200,00UIvitaminE.
dNonfibercarbohydrate=1000–([CP-CPofurea+urea]+NDF+EE+ash),Hall(2000). eEstimatedusingtheNRC(2001)model.
weighed,andthesilageandconcentrateofeachcowwereindividuallyhandmixedtoprepareatotalmixedration(TMR). Animalswerehousedinsandedbedfree-stallbarncontainingindividualpens(17.5m2),forcedventilationandfreeaccess towater.
2.2. Datacollection,samplingandanalysis
Samplesofingredients(0.5kg)werecollectedonceaweekduringthepreparationofconcentrate.Samples(0.5kg)ofsilage andortsfromeachcowweretakenoncedailyduringthemorningfeedingfromday15untilday21ofeachexperimental period,andcompositesamples(onasfed-basis)ofsilageandortsfromeachcowwereformedandstoredat−20◦Cfor furtherchemicalanalysis.Feedintakewasrecordeddailyasthedifferencebetweenfeedofferedandrefused.Sampleof feedandortsweredriedina55◦Cforced-airovenfor72handgroundtopassthrougha1mmscreen(WileyMill,ArthurH. Thomas,Philadelphia,PA,USA)andthenanalyzedfordrymatter([DM]method930.15;AOAC,2000),crudeprotein([CP]Nx 6.25;method984.13;AOAC,2000),etherextract([EE]method920.39;AOAC,2000),andash(method942.05;AOAC,2000). Neutraldetergentfiber(aNDF)wasdeterminedasdescribedbyMertensetal.(2002),using␣-amylase,withoutadditionof sodiumsulfitetothedetergent(AnkomTech.Corp.,Fairport,NY,USA),andwasexpressedwithresidualash.
Fecalsamples(0.5kgonwetbasis)werecollectedtwicedaily(0630hand1630h)fromday16untilday18ofeach experimentalperiod.Thesixfecalsamplesofeachcowwerecompositedintoasample(1.5kgonwetbasis)andstored at−20◦C.Indigestibleaciddetergentfiber(iADF)wasusedasaninternalmarkertoestimatefecalexcretionandapparent nutrientdigestibility.Samplesoffeeds,ortsandfecesweredriedat55◦Cinaforced-airovenfor72handgroundtopass througha2mmscreen(Wileymill,ArthurH.Thomas,Philadelphia,PA,USA).Thesesampleswereplacedinbagsof non-woventextile(100g/m2)followingtherecommendationofamaximumof20mgofdrysamplepercm2(Nocek,1988)and wereincubatedforaperiodof264hintherumenof2Holsteincows,previouslyadaptedtoahighconcentratediet,according tothetechniquedescribedbyCasalietal.(2008).After264h,bagswereremovedandwashedinrunningwater,driedat 55◦Cinaforced-airovenandsubjectedtoaciddetergenttreatment(Mertensetal.,2002).Totalfecalexcretionwasobtained asfollows:DMfecalexcretion(kg/d)=iADFintake(correctedfororts)/iADFcontentinfeces.
Cowsweremechanicallymilkedtwicedaily(0600hand1600h)andmilkyieldwasrecordedbyanautomaticmilkmeter (Alpro®,DeLaval–Tumba,Sweden).Milksampleswereautomaticcollected(Alpro®,DeLaval–Tumba,Sweden)fromday 16untilday18ofeachexperimentalperiod,accordingtomilkyieldofeachcowineachmilking.Sampleswererefrigerated afterthemorningmilkingandmixedwithsamplesoftheafternoonmilkingandanalyzedfreshforfat,crudeproteinand lactoseaccordingtoKaylegianetal.(2006).Milkyieldwascorrectedfor3.5%offataccordingtoSklanetal.(1992).
Bloodsampleswerecollectedond15ofeachperiodfromthecoccygealvesselsbeforethemorningfeeding,centrifuged at3000×gfor10minandplasmawasseparatedandstoredfrozenat−20◦Cuntilanalysis,asdescribedbyColaketal. (2013).Analyseswereperformedusingcolorimetriccommercialkits(Glucose:cat.no.K-082;Urea:cat.no.K-056;allfrom theBioclin,BeloHorizonte,Brazil),andreadingwasperformedwithasemi-automaticspectrophotometer(SBA200,CELM, SãoCaetanodoSul,Brazil).
Onday16and17ofeachexperimentalperiod,spoturinesampleswerecollectedfromeachcow4hafterthemorning feedingandthenfilteredtoobtain10mLaliquotswhichwereimmediatelydilutedin40mLof0.036Nsulfuricacid,toavoid bacterialdestructionofthepurinederivativesandprecipitationoftheuricacid,andthenstoredat−20◦Cforsubsequent analysisofuricacidandallantoinaccordingtoChenandGomes(1992).Apuresampleofurinewasstoredfordetermination oftotalnitrogen(N)andcreatinine.Concentrationsofuricacidandcreatinineweredeterminedusingcommercialkits(uric acidstableliquid:cat.no.k-052;kineticcreatinine:cat.no.K-067;Bioclin).Thedailyurinevolumewasestimatedfromthe dailycreatinineexcretionas24.05mgkg−1ofbodyweight(Chizzottietal.,2008).Theexcretionofuricacid,allantoinin urineandmilkwereconsideredasthetotalexcretionofpurinederivatives.Microbialproteinsynthesiswasestimatedas describedbyChenandGomes(1992).
Dataoftwosquarescomposedofcannulatedcowswereusedtoevaluateruminalfermentation,resultingin8repetitions foreachtreatmentpertime.Onday20ofeachexperimentalperiod,ruminalfluidsampleswerecollectedfromeight rumen-cannulatedcows(216±54DIMand596±27kgofBW)before(0h)and2,4,6,8,10and12hafterthemorningfeeding. TheruminalfluidpHvaluesweredeterminedusingapotentiometer(MB-10,MarteCientífica,SantaRitadoSapucaí,Brazil). Aliquotsofsamplesweremixedwithmetaphosphoricacid(0.25mol/LHPO3),centrifugedat7000×g,andsupernatant storedat−20◦CforanalysisofvolatilefattyacidsaccordingtomethoddescribedbyErwinetal.(1961)andadaptedby Getachewetal.(2002).Theremainingaliquotsofsamples(2mL)weremixedwith1mLofsulfuricacid(0.5mol/LH2SO4) andstoredat−20◦Ctodetermineammonianitrogen(NH3-N)byacolorimetricphenol-hypochloritemethod(Broderick andKang,1980).RuminalVFAweremeasuredusingagaschromatograph(GC-2014Shimadzu,Tokyo,Japan)equippedwith acapillarycolumn(Stabilwax,Restek,Bellefonte,PA,USA)at145◦C.Thegasesusedwerehelium(8.01mL/minflow)asthe carrier,hydrogen(pressureof60kPa)asthefuel,andsyntheticair(pressureof40kPa)astheoxidizer.Steamertemperature wassetat220◦C,ionizationdetectorflamesat250◦C,andtheseparationcolumnat145◦Cfor3min,whichwasthenraised 10◦C/minupto200◦C.Externalstandardwaspreparedwithacetic,propionic,isobutyric,butyric,isovalericandvaleric acids(Chemservice,WestChester,PA,USA).ThesoftwareGCsolution(Shimadzu,Japan)wasusedforcalculationofVFA concentrations.
Table2
Effectsofglycerinlevelsonintake,digestibilityandperformanceoflactatingdairycows.
Item Glycerininclusion,g/kgofDM SEMa P-valueb
0 70 140 210 Diet LIN
Drymatterintake,kg/day 21.97 21.97 21.42 21.06 0.32 0.05 0.04
Digestibility
Drymatter 0.696 0.703 0.717 0.724 0.003 <0.01 <0.01
Crudeprotein 0.734 0.736 0.755 0.772 0.003 <0.01 <0.01
Etherextract 0.729 0.761 0.841 0.869 0.008 <0.01 <0.01
Neutraldetergentfiber 0.599 0.580 0.571 0.543 0.005 <0.01 <0.01
Performance
Milkyield,kg/day 27.74 26.19 26.43 24.64 0.51 <0.01 <0.01
3.5%FCM,kg/dayc 31.74 30.24 30.30 27.89 0.52 <0.01 <0.01 Fat,kg/day 1.21 1.16 1.17 1.06 0.02 <0.01 <0.01 Protein,kg/day 0.87 0.82 0.83 0.78 0.02 <0.01 <0.01 Lactose,kg/day 1.31 1.21 1.24 1.16 0.02 <0.01 <0.01 FCM:DMId 1.49 1.38 1.42 1.33 0.03 0.01 <0.01 Milkcomposition Fat,g/kg 44.07 44.70 44.31 43.60 0.60 0.77 0.59 Protein,g/kg 31.41 31.38 31.40 31.52 0.12 0.84 0.52 Lactose,g/kg 47.10 47.04 47.00 47.17 0.17 0.87 0.75
Milknitrogen,g/day 136.52 126.78 130.15 121.38 2.51 <0.01 <0.01
Nitrogenefficiencye 23.69 22.00 22.48 22.08 0.41 <0.01 <0.01
aStandarderrorofmeans.
bTreatmenteffect(Diet).Linearcontrast(LIN).Quadraticcontrastsweretestedbutwerenotsignificant(P>0.05). c3.5%fatcorrectedmilk(FCM)=(0.432+0.165×fatcontent)×kgofmilk(Sklanetal.,1992).
dFatcorrectedmilktodrymatterintakeratio.
eNitrogen(N)efficiency=100×milkN(g/day)/Nintake(g/day).
2.3. Statisticalanalyses
ThedatawereanalyzedwithPROCMIXED(StatisticalAnalysisSystemforWindows9.0-SAS-SASInstituteInc.,Cary, NC,USA),accordingtothefollowingstatisticalmodel:
Yiklm=+Ti+Pk+Sl+Am(Sl)+eijklm
whereYiklmistheobservedvalueintheanimalm,fromlsquare,inthekthperiod,whichreceivedtheithglycerinlevel;
=overallmean;Ti=fixedeffectofglycerinlevel(3DF);Pk=fixedeffectofexperimentalperiod(3DF);Sl=fixedeffect ofsquare(5DF);Am(Sl)=randomeffectofanimalwithinsquare(18DF),andeijklm=randomresidualerror.Theruminal fermentationvariables(pH,NH3-NandVFA)wereanalyzedasrepeatedmeasuresusingPROCMIXEDofSAS9.0,considering inthestatisticalmodeltheeffectsofanimal,period,square,treatment(glycerinlevel),beyondtheeffectsoftimewith theirinteractionswiththetreatment.Compoundsymmetrywasthebestcovariancestructurebaseduponthesmallest Akaike’sinformationcriterionvalues.Othercovariancestructurestestedincludedheterogeneouscompoundsymmetry, unstructured,autoregressive1andheterogeneousautoregressive1.Resultsarereportedasleastsquaresmeans.Responses toglycerinlevelweretestedwithlinearandquadraticcontrasts,whichweredeclaredsignificantatP<0.05.
3. Results
InclusionofcrudeglycerininthedietslinearlydecreasedtheDMI(P=0.04;Table2).Cowsfeddietscontaining210g/kg ofcrudeglycerinreducedDMIby4.1%or0.910g/dcomparedtocowsfedcontroldiet.TotaltractdigestibilityofDM,CP,and EElinearlyincreased(P<0.01),butneutraldetergentfiber(NDF)digestibilitylinearlydecreased(P<0.01)accordingtothe inclusionofdietarycrudeglycerin.Neutraldetergentfiberdigestibilityreduced5.6%incowsfeddietscontaining210g/kg ofcrudeglycerincomparedtocontrol.Increasingthedietaryinclusionofcrudeglycerinlinearlydecreasedmilkyield, fat-correctedmilk(FCM),milkefficiency(FCM:DMI),fat,proteinandlactose(P<0.01,Table2).However,milkfat,proteinand lactoseproportionweresimilaramongtreatments(P>0.05).DailyNmilkexcretionandNefficiencywerelinearlydecreased (P<0.01)withcrudeglycerininclusioninthediet.
TotalruminalVFAconcentrationwassimilaramongtreatments(P>0.05;Table3).However,theinclusionofcrude glyc-erinindietslinearlydecreasedruminalacetate,acetatetopropionateratio(P<0.01),whereaspropionateandbranchedchain fattyacids(BCFA)linearlyincreased(P<0.01)withcrudeglycerininclusion.Butyratewasquadraticallyaffected(P<0.01)by crudeglycerin,withhighestvalueobservedwiththedietaryinclusionof70g/kgDMofcrudeglycerin.Therewasdiet*time interactionforruminalpH,butyrateproportionandacetatetopropionateratio(P<0.01).RuminalNH3-Nconcentration linearlydecreased(P<0.01)withcrudeglycerininthediet.Microbialproteinsynthesiswasnotaffectedbycrudeglycerin treatments(P>0.05).Bloodconcentrationofglucoselinearlyincreased(P<0.01;Table3)from78.84(control)to86.40mg/dL
Table3
Effectsofglycerinlevelsonruminalparametersandbloodmetabolitesinlactatingdairycows.
Item Glycerininclusion,g/kgofDM SEMa P-valueb
0 70 140 210 Diet Time Diet*Time LIN QUAD
pH 6.31 6.38 6.38 6.32 0.03 0.65 <0.01 <0.01 0.89 0.22
NH3-N,mg/dL 23.74 21.52 18.05 17.54 0.49 <0.01 <0.01 0.19 <0.01 0.39
TotalVFA,mmol/L 119.11 111.40 108.16 113.87 2.26 0.41 <0.01 0.85 0.37 0.16
Acetate,mol/100mol 62.41 52.51 51.13 47.16 0.58 <0.01 <0.01 0.44 <0.01 0.05
Propionate,mol/100mol 20.61 22.47 24.02 29.12 0.32 <0.01 <0.01 0.06 <0.01 0.06
Butyrate,mol/100mol 12.13 19.25 18.93 17.56 0.35 <0.01 <0.01 <0.01 <0.01 <0.01
BCFA,cmol/100mol 4.85 5.77 5.92 6.16 0.07 <0.01 <0.01 0.07 <0.01 0.11
C2:C3d 3.05 2.39 2.21 1.73 0.05 <0.01 <0.01 <0.01 <0.01 0.20
MicrobialCP,eg/day 2446 2415 2250 2323 67.18 0.43 – – 0.20 0.57
Bloodmetabolites
Glucose,mg/dL 78.84 83.93 83.96 86.40 0.74 <0.01 – – <0.01 0.30
BUN,fmg/dL 36.95 32.50 32.26 33.36 0.76 0.01 – – 0.13 0.01
aStandarderrorofmeans.
b Treatmenteffect(Diet).Timeeffect.Dietandtimeinteractioneffect(Diet*Time).Linearcontrast(LIN).Quadraticcontrasts(QUAD). c BCFA:branchedchainfattyacids(includedvalerate,isovalerateandisobutyrate).
d Acetatetopropionateratio. eMicrobialcrudeprotein. f BUN:bloodureanitrogen.
(210g/kgDMofcrudeglycerin);ontheotherhand,bloodureanitrogenconcentrationwasquadraticallyaffectedbycrude glycerin(P=0.01),withlowestvalueobservedwhen140g/kgDMofcrudeglycerinwassupplied.
4. Discussion
Currently,thegrowthofthebiodieselindustryhasresultedingreateravailabilityofcrudeglycerin,aby-productanda potentialreplacertostarchindietsofdairycows.InthecurrentstudyalineardecreaseinDMIwasobservedwhencows werefedupto210g/kgDMofcrudeglycerin.Ezequieletal.(2015)reportedareductionof15%inDMIofdairycowsfed crudeglycerinupto300g/kgofdietDMcomparedtocontrol.Thenegativeeffectsofcrudeglycerinonanimalmetabolism andperformancemightbeattributedtothreefactors:thequalityofcrudeglycerinduetoimpurities,includingmethanol andsalts(ThompsonandHe,2006;Chungetal.,2007);thespeedinwhichglycerolisfermentedinrumen(Remondetal., 1993;Wangetal.,2009;Shinetal.,2012);andtheabilityofrumenepitheliumtoabsorbglyceroltobemetabolizedinliver (Krehbiel,2008).Ezequieletal.(2015)demonstratedthatdietswith300g/kgDMofcrudeglycerinincreased500%ofNaCl dietarycontentanddecreasedfeedintakeofdairycows.Furthermore,highsaltsandsodiumdietarylevelscouldresultinan electrolyteunbalanceinanimalsandaffectacceptabilityofthedietwithcrudeglycerin(Chungetal.,2007;Dasari,2007). Ontheotherhand,crudeglycerinhashighenergycompounds,andcaninfluenceoxidationreactionsandincreaseKrebs cycleintermediatesproductionintheliver,stimulatingsatietyandreducingDMI(Bensonetal.,2002;Trabueetal.,2007; Allenetal.,2009).
Inclusionofhighdietarylevelsofcrudeglycerin(210g/kg)indairycowdietsresultedinalargedecreaseofmilkyield (3.1kg/day).Similarly,Boydetal.(2013)foundreducedmilkyieldwhencrudeglycerinwasaddedtothedietofdairycows. However,thisresultcontrastedwithotherpreviousstudiesthatreportednodifferenceinmilkyieldwithglycerinadded tothedietsofmid-lactationdairycows(Donkinetal.,2009;Kassetal.,2012;Shinetal.,2012)whichusedupto150gof glycerinindietDM.Inthecurrentstudy,thedecreaseofmilkyieldcouldberelatedtoDMIanddietcomposition.Despite thedigestibilityofnutrientsincreasedwithcrudeglycerin,dietaryCPcontentandDMIdecreased,andconsequentlyaltered metabolizableproteinavailabletobeabsorbedintheduodenum.Oncethemilkcompositionwasnotaltered,theyieldof solidscomponentsinmilk(fat,proteinandlactose)wouldhavethesameresponseofmilkyield.
Apparenttotal-tractdigestibilityofDM,CPandEEincreasedwhenglycerinwasaddedtothediets.Theseresultsarein agreementwithapreviousstudyinwhichglycerincomprisedupto150g/kgofthediet,resultinginincreaseddigestibility ofDM(Donkinetal.,2009).DespitetheincreaseofDMdigestibilitywhencrudeglycerinwasaddedtodiets,theFCMtoDMI ratiolinearlydecreased.Thelatterreducedbecausethedecreaseofmilkyieldwasproportionallyhigherthanthedecrease ofDMI,mainlywhencowswerefedthehighestlevelofcrudeglycerin(−4.0%vs.−11.1%,respectively).Furthermore,in thecurrentstudy,highcrudeglycerinlevelshadanegativeeffectonNDFdigestibility.Invitrostudiesshowedthatglycerol hasaninhibitoryeffectontheactivityandgrowthofcellulolyticbacteria(Rogeretal.,1992;AboEl-Noretal.,2010),which mayimpairtheNDFdigestibility.OtherinvivostudiesalsoshoweddecreaseofNDFdigestibilitywithdietaryinclusionof glycerinupto150g/kgofDM(Donkinetal.,2009;Shinetal.,2012).Moreover,inthisstudythereducedNDFdigestibility mightbeassociatedwithchangesinpropionateandacetateconcentrations,suggestingthattherewereshiftsintheruminal microorganism;however,thisexplanationshouldbeevaluatedinfurtherstudies.
InclusionofcrudeglycerininthecurrentstudyalteredtheruminalVFAproportions.ThesechangesinVFAconcentrations aresimilartothosereportedinpreviousstudies.Decreaseinacetateandincreaseinpropionate,butyrateandBCFAruminal
fluidconcentrationswerefoundwhendairycowswerefedglycerin(Carvalhoetal.,2011;Kassetal.,2012;Shinetal.,2012). Theincreaseofruminalpropionateconcentrationisrelatedtothefactthat30–69%ofglycerolconsumedisfermentedin therumen,andmostglycerolisfermentedintopropionate(Remondetal.,1993),suggestingthatruminaldegradationof glycerinwasfasterthangroundcornandsoybeanmealdegradation.Propionateismorehypophagiccomparedtoacetate becauseofitsabilitytostimulateoxidationintheliver(Allen,2000).Furthermore,glycerolisaprecursorofglucoseand mayenterintothegluconeogenicpathwaybeingconvertedtoglucoseintheliver,providingenergyforthecow(Goofand Horst,2003;Allenetal.,2009).Therefore,anotherexplanationforthedecreasedDMIreportedinthecurrentexperimentis relatedtothehepaticoxidationtheory,whichstatesthathepaticfueloxidationincreasesATPconcentrationsinhepatocytes whichsendinhibitorysignalsviavagusnervetonucleustractussolitariesthatinhibithypothalamicsatietycenters(Allen etal.,2009).
ThedecreasedNH3-NruminalconcentrationinthepresentstudymayberelatedtodietcompositionandDMI.TheCP contentofdietsdecreasedandDMIlinearlydecreasedaccordingtotheinclusionofcrudeglycerin;thus,lessproteinwouldbe availableintherumenenvironmenttobedegradedintoNH3whencowswerefeddietswithcrudeglycerin.Indeed,microbial proteinsynthesiswasnotimpairedwhencrudeglycerinwasincludedupto150g/kgofthediet(Donkinetal.,2009;Shin etal.,2012),showingnoeffectsofcrudeglycerinonruminalNsupply.Plasmaglucoseconcentrationincreasedaccordingto dietaryinclusionofcrudeglycerinandthisresultcanberelatedwithincreaseinruminalpropionateconcentrations,which isaglucogenicprecursor.Bloodglucoseconcentrationwasdecreased(Carvalhoetal.,2011),unchanged(Kassetal.,2012; Shinetal.,2012;Boydetal.,2013),orincreased(Donkinetal.,2009)whenglycerinwasaddedupto150g/kgincowdiets. Thedifferencesamongthesestudiescouldberelatedtothepurityofglycerin,amountofglycerinadded,andthetimeof bloodsamplingrelativetomealtime.
5. Conclusion
Inclusionofhighlevelsofcrudeglycerin(210g/kg)inthedietsofmid-lactatingcowsincreaseddrymatterdigestibility andruminalpropionate,butnegativelyaffecteddrymatterintakeandmilkyield.Inaddition,resultssuggestthatcrude glycerinhasthepotentialtopartiallyreplacestarchindietarylevelsbelowof140g/kgDMwithoutlargelyreducedairycow performance.
Conflictofinterest
Theauthorsdeclarethatthereisnoconflictofinterest.
Acknowledgements
TheauthorsacknowledgetheUniversityofSãoPaulo(USP)andtheDairyCattleResearchLaboratory,forproviding allthephysicalstructureandstaffnecessaryforthisstudy.Inaddition,theauthorsexpressappreciationtotheBrazilian fundingagencyCAPES(‘Coordenac¸ãodeAperfeic¸oamentodePessoaldeNívelSuperior’)forscholarshiptoP.G.Paiva(grant numberBEX3664/14).
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