Rev Colomb Cienc Pecu 2017; 30:11-20

Revista Colombiana de Ciencias Pecuarias

Original articles

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Performance and serum parameters of growing pigs fed semi-purified glycerin¤

Desempeño productivo y parámetros séricos de cerdos en crecimiento alimentados con glicerina semi-purificada

Desempenho e parâmetros séricos de suínos em crescimento alimentados com glicerina semipurificada

Guiomar H Verussa1, Zoot, MSc; Anderson Corassa1*, Zoot, PhD; Douglas S Pina1, Zoot, PhD; Ana P S Ton1, Zoot, PhD; Cláudia M Komiyama1, MV, PhD; Alexandre O Teixeira2, Zoot, PhD.

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.

2Departamento de Zootecnia, Universidade Federal de São João Del Rei, Praça Frei Orlando, 170, Centro, CEP 36307-352, São João Del-Rei, MG, Brasil.

(Received: November 16, 2015; accepted: August 16, 2016)

doi: 10.17533/udea.rccp.v30n1a02

¤ Tocitethisarticle:VerussaGH,CorassaA,PinaDS,TonAPS,KomiyamaCM,TeixeiraAO.Performanceandserumparametersofgrowingpigsfedsemi-purifiedglycerin.RevColombCiencPecu2017;30:11-20.

* Correspondingauthor:AndersonCorassa.ProgramadePósGraduaçãoemZootecnia,UniversidadeFederaldeMatoGrosso,CampusdeSinop.AvenidaAlexandreFerronatoNº1.200,SetorIndustrialCEP78557-267,Sinop,MT,Brasil.Tel.:+556698423-5671.E-mail:anderson_corassa@ufmt.br

Abstract

Background:theuseofsemi-purifiedglycerininpigdietshasbeenstudiedasanalternativeenergysource.Objective: toevaluategrowthperformanceandserumlevelsofglucose,triglycerides,cholesterol,andureainpigsfeddietscontainingsemi-purifiedglycerinduringthegrowthphase.Methods: fortybarrowswithaninitialweightof27.30±1.74Kg,distributedinarandomizedcompleteblockdesignwithfourtreatmentsandfivereplicateswereused.Thedietarytreatmentswereacombinationofcornandsoybeanmealdietswiththeadditionof0,5,10or15%semi-purifiedglycerin.Theexperimentalperiodlasted27daysandwasdividedintotwoperiods.Results: duringPeriod1,pigperformancedidnotdifferwiththeinclusionofsemi-purifiedglycerin in thediet. InPeriod2,an improvement inaveragedailyweightgainwasobserved.In the totalperiod,animprovementwasobservedintheaveragedailyweightgain,feed/gainratioandfinalweightoftheanimals.However,serumparameterswerenotaffectedbytheinclusionofsemi-purifiedglycerininthediets.Conclusion: theadditionofupto15%semi-purifiedglycerintothedietofgrowingpigsimprovesgrowthperformancewithoutaffectingserumparameters.

Keywords: cholesterol, co-product, glucose, glycerol, triglycerides, urea.

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Resumen

Antecedentes: elusodelaglicerinasemi-purificadaenladietadecerdossehaestudiadocomounafuentealternativadeenergía.Objetivo:evaluareldesempeñoylosnivelesséricosdeglucosa,triglicéridos,colesterolyureaencerdosalimentadoscondietasquecontienenglicerinasemi-purificadadurantelafasedecrecimiento.Métodos:fueronutilizados40machoscastradosconunpesoinicialde27,30±1,74Kg,distribuidosenundiseñoexperimentalenbloquesalazarconcuatrotratamientosycincorepeticiones.Lostratamientossebasaronenmaízyharinadesojaconadiciónde0,5,10o15%deglicerinasemi-purificada.Elperíodoexperimentalduró27días,divididoendosperíodos.Resultados: enelperíodo1,eldesempeñoproductivodeloscerdosnofuealteradoporlainclusióndeglicerinasemi-purificadaenladieta.Enelperíodo2seobservóunamejoraenlagananciadiariadepeso.Enelperíodototalseobservóunamejoraenlagananciadiariadepeso,conversiónalimenticiayelpesofinaldelosanimales.Losparámetrosséricosnoseafectaronporlainclusióndeglicerinasemi-purificadaenladieta.Conclusión:laadicióndeglicerinasemi-purificadahastaenun15%enladietadecerdosencrecimientomejoraeldesempeñoproductivo,sinafectarlosparámetrosséricos.

Palabras clave: colesterol, co-producto, glicerol, glucosa, triglicéridos, urea.

Resumo

Antecedentes:utilizaçãodaglicerinasemi-purificadanaalimentaçãodesuínosvemsendoestudadacomoumafontealternativadeenergia.Objetivo: avaliarodesempenhoeníveisséricosdeglicose,triglicerídeos,colesteroleuréiaemsuínosalimentadoscomdietascontendoglicerinasemi-purificadanafasedecrescimento.Métodos: foramutilizados40machoscastradoscompesoinicialde27,30±1,74Kg,distribuídosemdesenhoexperimentaldeblocoscasualizadoscomquatrotratamentosecincorepetiçõesportratamento.Ostratamentosforambaseadosemmilhoefarelodesojacomadiçãode0,5,10ou15%deglicerinasemi-purificada.Operíodoexperimentaldurou27diasdivididoemdoisperíodos.Resultados: noperíodo1odesempenhodossuínosnãofoialteradopelainclusãodeglicerinasemi-purificada.Noperíodo2foiobservadomelhoranoganhodepesodiário.Noperíodototalobservou-semelhoranoganhodepesodiário,conversãoalimentarepesofinaldosanimais.Osparâmetrosséricosnãoforamafetadospelainclusãodeglicerinasemi-purificadanas dietas. Conclusão:aadiçãodeaté15%deglicerinasemi-purificadaemdietasdesuínosemcrescimentomelhoraodesempenhoenãoalteraosparâmetrosséricos.

Palavras chave:colesterol, co-produto, glicerol, glicose, triglicerídeos, ureia.

Introduction

Biodiesel is produced from vegetable oils oranimalfats,andBrazilisamongthelargestproducersand consumers of biofuel in theworld due to itshigh production and availability of rawmaterials(Cremonezet al.,2015).Thedemandandproductionofbiodieselhasboostedtheavailabilityofglycerin,themaincoproductofbiodieselproduction(Adilsonet al., 2011).Among the potential applications,glycerinhasbeenstudiedasanalternativefeedforpigs because it has a palatable sweetness and anenergyvaluesimilartocorn.Therefore,thisingredientcanbe used as a sourceof energy for pigs duringdifferentgrowthstages(Huepaet al.,2015;Madridet al.,2013).

Glyceridesmaypresentvariationincompositionduetodifferencesintherawmaterialsaswellastheprocessesemployedintheproductionofbiodiesel.

All these generate varying degrees of purity(Oliveiraet al.,2013)andnutritionalvalue,especiallyinregardstoglycerolandfattyacidscontent(Kerret al.,2009).

Groesbecket al.(2008)recommendedtheinclusionof12%crude glycerol in thedietofgrowingpigs.Theyreportedanincreaseindailyweightgainandfeedintake,aswellasimprovedphysicalpropertiesofpellets.Bycontrast,Gallegoet al.(2014)reportedthatdietaryadditionofsemi-purifiedglycerinupto14%didnotaffectfeedintake,weightgain,norfeed/gainratioofgrowing-finishingpigs.Thesedifferencesinresultsshowthatthereisnogeneralconsensusinarrivingattheoptimaldietarylevelofglycerinthatcanberecommendedforpigs.

In monogastric animals, dietary glycerol isabsorbedbythestomachandintestinesandtransportedtothelivertobemetabolized.

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Thus,dependingon thenutritionalstatusof theanimal, glycerol canbeused in lipid formationorenergyproduction.Inasituationofsurplusenergy,glycerolactsasaprecursoroftriglyceridesynthesis,while in anenergy shortage situation, it isused tosupplycarbonskeletonsforgluconeogenesisorforenergy production through glycolysis andKrebs’scycle(Lin,1977).However,fewstudies(Hansenet al.,2009;Huepaet al.,2015)haveinvestigatedhowtheuseofglycerolinpigdietsaffectsmetabolism.

Thisstudyaimedtoevaluatetheeffectsofaddingincreasingamountsofsemi-purifiedglycerin to the dietsofgrowingpigs,andstudygrowthperformanceandserumlevelsofglucose,triglycerides,cholesterol,and urea.

Materials and Methods

Ethical considerations

This studywascarriedout inApril2015at theUniversidade Federal deMatoGrosso, CampusUniversitáriodeSinop(Brazil).ThestudyprotocolwasconsistentwiththeethicalprinciplesforanimalexperimentationadoptedbytheNationalCouncilforAnimalExperimentationControl,andwasapprovedby the Ethics Committee onAnimalUse of theUniversidade Federal deMatoGrosso (protocol23108.700673/14-4).

Husbandry and diets

Fortycommercialbarrows,withanaveragebodyweightof27.30±1.74Kgwereusedintheexperiment.Pigswerehousedinabricksheddividedinto20pens,withasbestoscementtiles.Thepenshadfeedersinthefrontandnipplewaterersinthebackarea.Theanimalswererandomlydistributedinacompleteblockdesignwithfourtreatments,fivereplicatespertreatmentandtwoanimalsperexperimentalunit(pen).Initialbodyweightofthepigswasusedasthecriterionfortheformationoftheblocks.

Thetreatments(Table1)consistedofcorn-soybeanmealdietscontaining0,5,10,or15%semi-purifiedglycerin. Dietary treatments were formulatedfollowingRostagnoet al. (2011)recommendations.

The salt content was adjusted to provide therecommendedlevelsofsodium.However,dietswith0and5%semi-purifiedglycerinwereaddedwithmoresaltthanthe10and15%dietsduetothehigherconcentrationofmineralsinglycerin.

Semi-purifiedglycerin(Table2)wasobtainedfromasoybeanoilbiodieselproducingcompany,and had 3,280Kcal/Kgmetabolizable energy(Verussa,2015).

Feedandwaterwereofferedad libitum to the pigs throughout the experimental period. Pencleaningwithscrapingofwastewasconducteddaily;waterblastingwasperformedweekly.

Data collection and chemical analysis

Theexperimentlasted27daysandwasdividedinto twoperiods: Period 1: days 0-20, andPeriod2: days 21-27.The animalswereweighed at thebeginning and end of each period, and the feedquantities and leftoverswere recorded.These datawereusedtocalculatetheaveragedailyfeedintake(ADFI), average dailyweight gain (ADWG), andfeed/gainratio(FGR)oftheexperimentalunits.

In themorning of the first (initial) and last(final)daysof theexperiment,8mLofbloodwascollectedfromthe jugularveinofallanimalsafteran8-hfasting.Then,4mLofbloodweretransferredintovacuum tubes containinggel tab todeterminetriglycerides, cholesterol and urea levels.Other 4mLofbloodweretransferredintotubescontainingsodiumfluorideforglucoseanalysis.

All sampleswere centrifuged at 3,000 rpm for15min immediately after collection. Serumwasobtainedfromthetubeswithagelseparator(VacuettedoBrasilLtda,Campinas,SP,Brasil), andplasmawith sodiumfluoridewas transferred into cryovialtubes,whichwere then labeled and refrigerateduntil laboratory analysis on the same collection.LABTEST® diagnostic kits (LabtestDiagnósticaS.A.,LagoaSanta,MG,Brasil)containingreagentsfor theanalysisofurea (sodiumsalicylate,sodiumnitroprusside,andurease),glucose(glucoseoxidase,peroxidase, 4-aminoantipyrine, phenol, sodiumazide, and surfactants), cholesterol (phenol,

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Table 2. Chemical composition of semi-purified glycerin.

Parameter Result

Water (%) 11.99

Sulfated ash (%) 6.57

Glycerol (%) 78.50

Methanol (%) 0.08

Chloride (%) 3.65

Chloride with NaCl (%) 6.00

pH 3.00

Total fatty acids (%) 7.00

Gross energy (Kcal/Kg) 4,111

Source: Relatório de ensaio Tanque 344-2-012 de 10 de fevereiro de 2015. Fiagril Ltda, Lucas do Rio Verde, MT, Brasil.

Table 1. Composition (dry matter basis) and nutritional value of the diets containing semi-purified glycerin.

Ingredients (g/Kg) Semi-purified glycerin (%)

0 5 10 15

Corn 760.0 702.0 642.1 580.8

Soybean meal 208.4 219.5 230.5 242.0

Semi-purified glycerin 0 50.0 100.0 150.0

Dicalcium phosphate 16.6 16.8 17.0 17.2

Salt 4.0 1.1 0 0

Limestone 4.0 3.8 3.7 3.5

Soybean oil 4.0 4.0 4.0 4.0

L-lysine HCL 1.0 0.8 0.7 0.5

Mineral-vitamin premix1 2.0 2.0 2.0 2.0

Calculated composition

Metabolizable energy (Kcal/Kg) 3,230 3,230 3,230 3,230

Crude protein (%) 15.80 15.80 15.80 15.80

Calcium (%) 0.63 0.63 0.63 0.63

Available phosphorus (%) 0.33 0.33 0.33 0.33

Sodium (%) 0.18 0.18 0.26 0.38

Chloride (%) 0.29 0.29 0.40 0.58 Digestible lysine (%) 0.77 0.77 0.77 0.77

Digestible methionine (%) 0.23 0.23 0.23 0.23

Digestible methionine + cystine (%) 0.47 0.47 0.47 0.47

Digestible threonine (%) 0.52 0.52 0.52 0.52

Digestible tryptophane (%) 0.16 0.16 0.16 0.161Composition per Kg of diet: Cu (1,000 mg), Fe (6 mg), Zn (8 g), Mn (3 g), Se (28 mg), I (80 mg), Co (50 mg), cholin (10 g), vitamin A (550,000 IU), vitamin D3 (125,000 IU), vitamin E (3,000 IU), vitamin K3 (250 mg), nicotinic acid (2 g), pantothenic acid (1,200 mg), folic acid (25 mg), biotin (1 mg), vitamin B1 (80 mg), vitamin B2 (250 mg), vitamin B6 (160 mg), vitamin B12 (600 µg), etoxiquin100 mg), BHT (240 mg), colistine (3.2 g).

sodiumcholate,sodiumazide,4-aminoantipyrine,cholesterol esterase, cholesterol oxidase, and peroxidase), and triglycerides (magnesiumacetate,4-chlorophenol, 4-aminoantipyrine, lipoproteinlipase,glicerolquinase,andsodiumazide)wereused,alongwith a semiautomatic biochemical analyzer(AAKERSolutionsLtda,PortoAlegre,RS,Brazil)fordeterminationofserumparameters.

Statistical analysis

The experimentwas carried out according toa randomized complete block design,with initialbodyweightoftheanimalsusedtoformtheblocks.Analysisofvariancewasconductedaccordingtothestatisticalmodelshownbelow:

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Yijk =μ+Gi+Bj +εijk

Where:

Yijk =istheobservationregardingtheeffectofiglycerinlevel,jblockandkreplicate.

Gi =istheeffectofglycerininclusionlevels.

Bj =istheeffectofjblocks.

εijk = is the random error associatedwith eachobservation.

The effects of glycerin levelswere evaluatedby partitioning the treatment sumof squares intoorthogonal contrasts to assess the linear, quadratic and cubiceffects.Theevaluationshadanerrorprobabilityof 0.05 for type I.Thedatawere subjected to themixed procedure of the SAS software Statistical

AnalysisSystem-Version6- (SASInstitute, Inc.,Cary,NC,USA),with5%probability.

Results

Performance

In Period 1, growth performance of the pigsshowednodifference(p>0.05)causedbytheglycerinlevel(Table3).InPeriod2,alinearincreaseinADWG(p

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with those animals fed increasingdietary glycerin levels showing increasedfinalweights.The otherperformanceparameterswerenotinfluenced(p>0.05)bytheinclusionof glycerin(Table3).

Serum biochemical indicators

Theserumlevelsofurea,cholesterol,triglyceridesand glucose were not affected (p>0.05) by theinclusionofglycerininthediet(Table4).Therewasanincrease(p0.05)betweenbothcollections.

Discussion

Glycerineffectswerenotobservedonfeedintakedespitethehighsodiumcontentindietswithhigherinclusionofglycerin.IncreaseinADFIofpigsfeddietscontainingglycerincanbeexpectedduetothesweetflavorofglycerin,whichimprovespalatability

(Groesbecket al., 2008), however, higher sodiumcontent can limit feed intake. The acidificationprocesses (HCl)used forglycerinpurification,andthe neutralization base (NaOH;Ooi et al., 2004)used to adjust pH can alter its composition andproduceglycerinthatisapproximately80%glycerolwithlowmethanollevelsandincreasedNaClandKlevels(Gallegoet al.,2014).Carvalhoet al.(2013)utilizedcrudeglycerin,whileGallegoet al.(2014)andGonçalveset al. (2013) utilized semi-purifiedglycerin and achieved similar results, reportingnoeffectsonfeedintake.

However,Schiecket al.(2010)observedthatpigsfedadietwith8%crudeglycerinhadgreaterADFIcomparedtothecontroldiet.AstudybyZijlstraet al. (2009),registeredthatnurserypigsfedwheat-baseddietscontaining0,4and8%crudeglycerin,increasedADFIquadratically.Stevenset al.(2008)alsofoundthat crude glycerin had a positive linear effect onADFI.Thesedifferentresponsesinfeedintakecouldbe due to themarginal reduction inmetabolizableenergyofdietscontainingglycerinwheningredient

Table 4. Serum biochemical indicators of growing pigs fed diets containing semi-purified glycerin.

Collect Glycerin (%) Significanceingredients (g/Kg)

Significancecollect

CV (%)3

0 5 10 15 Average Linear Quadratic Cubic

Urea (mg/dL)

Initial 25.62 26.59 26.69 25.54 26.11 0.9862 0.5610 0.9606

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substitutionswere not corrected to achieve similarenergyvalues in thediets.Thismighthavealteredfeedintake.

The energy value of glycerin is dependent onits composition, particularly its glycerol and fattyacidcontents,whichareinverselyproportionalandarerelatedtotheproductionefficiency(Kerret al., 2009).Thecommonlycalledpureglycerinhasmoreglycerol and less fatty acid contents.On the otherhand, glycerinwith less glycerol andmore fattyacids canhave higher energy content. In addition,methanol, sodium andmineralmatter levelsmayalso impair the quality of the product,which hasled to the establishment of a quality standard inBrazil(BRASIL,2010).GottandEastridge(2010),analyzing 16 samples of glycerin obtained fromdifferentrawmaterialsandindustries,statedthattheashcontenthasawidevariationduetothequantumofcatalystsusedineachindustry.Oliveiraet al.(2013),analyzing41samplesofglycerinfrom16biodieselplants,registered0.61-2.82%sodiumlevels,and2.3-12.1%mineralmatterlevels,whichdemonstratesitshighvariation.

TheADWGincreaseinPeriod2andtheFCRandADWGimprovementsinthetotalexperimentalperiodmayberelatedtoapossibleimprovementinnutrientdigestibilityduetoinclusionofglycerininthediet.Madrid et al. (2013)statedthatcrudeglycerincouldbeconsideredasahighlydigestiblefood,andfounda linear increasing effect on nutrient digestibilitycoefficients in pigs fed diets containing glycerin.Furthermore,ilealdigestibilityofglycerolisveryhigh(>99%)fordietscontainingcrudeglycerin(Oliveiraet al.,2014).Inaddition,Silveiraet al.(2015)evaluatedcrudeglycerin (0, 5, 10, and15%), and registeredthatthedigestibleenergycoefficientincreasedwiththeadditionofglycerin,duetothefactthatitisverydigestible comparedwith regular feed.AccordingtoRobergsandGriffin(1998),glycerolisabsorbedthrough the portal systemandgoes straight to theliver;afterthat,glycerinistransformedintoglycerol-3-phosphatebyglycerolkinase,andthenitisoxidizedtodihydroxyacetonephosphateontheouterfaceoftheinnermitochondrialmembrane,andgoesthroughtheglycolyticpathwayforenergyproduction.TheresultsofthepresentstudyareinagreementwithOrengoet

al.(2014),whofoundhigherADWGvaluesinpigsfed10%crudeglycerincomparedwithacontroldiet.

Nevertheless, our results differwith previousworks that foundno difference in performanceofgrowing pigs fed dietswith 10% crude glycerin(Lammerset al.,2008),12%semi-purifiedglycerin(Gonçalves et al., 2013), 14% semi-purifiedglycerin (Gallego et al.,2014),andupto16%semi-purifiedglycerin(Gonçalveset al.,2014).However,thosestudiesreportedthatglycerincouldbefedtogrowingpigsatthoselevelswithoutadverseeffectsonanimal’sperformance.

Bycontrast,Madridet al. (2013)foundadecreaseinADWGandADFIofgrowingpigsbytheadditionof 5% crude glycerin in the diet; such decreaseadverselyaffectedanimalperformance.Theauthorsattributedthevariabilityofresultsregardingtheuseofglycerintotheprecisionofeachstudyindetectingstatisticallysignificantdifferences,thepurityoftheglycerinused, andpossible interactionswithotheringredients in the diet.

The improvement ingain inPeriod2alongsidewith the lack of effect on growth performance inPeriod1suggeststhatglycerindoesnotaffectanimalperformanceintheshortterm;however,ifthelengthofthefeedingperiodisincreased,glycerinmayaffecttheperformanceofpigs.Thisis inagreementwithSchiecket al.(2010),whoevaluatedacorn-soybeanmeal control diet, long-term and short-term crudeglycerindiets,andregisteredthatpigsfedalong-termdiethadgreaterADWGthanthecontroldiet,whiletheshort-termdiethadanADWGsimilartothecontrol.Berenchteinet al.(2010),whostudiedpigsfedupto9%semi-purifiedglycerinindifferentgrowthperiods,also foundnodifference in theperformance in thefirstperiodofevaluation(33-65Kgofbodyweight);however,incontrastwiththepresentstudy,adecreaseinADWGwasobservedintheirsecondperiod.

Serum biochemical indicators

Ingrowingswine,80%offattyacidisaresultofde novosynthesis,usingglucoseassubstrate,becauseonlyalowproportionofcaloriesintheirnormalfeedispresentasfattyacids,andabout40%bodyglucose

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usageisdestinedforfatdepositioninadiposetissue(Joséet al.,2006).Theadditionofglycerinreducedcorninclusionintheexperimentaldietsand,therefore,lowerthesubstrateforsynthesisandtransportoffattyacidsbytheliver,suggestingareductionofcirculatingcholesterolandtriglycerides.However,thiswasnotobservedinthisstudy,possiblybecausethedietshadthesamemetabolizableenergy,drivingtheanimalsatthesameenergybalanceand,consequently,thesamepotentiallipogeniclevels.

Lin (1977), using glycerol, andGallego et al. (2014)usingsemi-purifiedglycerin,studiedglycerolasa sourceof readilyavailableenergy.Dependingonthenutritionalstatusoftheanimal,glycerincanbeusedtoformlipidsortoproduceenergybyusingglucose.Therefore,inthisstudy,theglycerinaddedisassumedtoaffecttheserumlevelsofsubstancesthat are involved inmetabolism.However, thishypothesiswas not confirmedby the experimentalresultsobtainedinthepresentworkduetotheabsenceofeffectofglycerininclusiononserumparameters.

TheseobservationsareinagreementwithGallegoet al.(2014),whofoundnodifferencesintheserumlevelsofglucose,cholesterolandplasmatriglyceridesinpigsfeddietscontainingupto14%semi-purifiedglycerin.Withincreaseddietaryglycerol,bloodlevelsofglycerolmayalsoincrease(Kijoraet al.,1995),but themetabolism of excessive plasma glyceroloccur through gluconeogenesis (Gallego et al.,2014).Similarly, Hansen et al.(2009),Madridet al. (2013)andOliveiraet al.(2014)foundthatinclusionof5,16,and18%crudeglycerininthedietofpigshadnoeffectonplasmaglucose.Huepaet al. (2015)alsoshowed that inclusion of up to 12% semi-purifiedglycerininpigdietshadnoeffectonbloodglucoselevels; however, inclusion of glycerin promoted alinear increase in triglyceride content. The authors explained that the increased triglycerides in bloodwas associatedwith the increased concentrationof free fatty acids and glycerol,with part of thelatterdrivenfromthebloodstreamtothetissuesforenergyproduction.Similarly,Carvalhoet al.(2012)registeredaquadraticeffectoncholesterollevelsofpigsfeddietscontainingupto12%crudeglycerin.

Thelengthoftheperiodofsupplymayhavebeeninsufficienttosignificantlyaffectserumparameters.

Differing from the present results,Carvalhoet al. (2012)observedan increase inplasma triglyceridelevels in relation to the sampling period (sampleofthe14thand22nddays),possiblyduetotheneedforalongerperiodofadaptationtodietscontainingglycerin.

Regardingurea, the results of thepresentworkindicatedthatwhenupto15%semi-purifiedglycerinwasprovidedtogrowingpigs,thereisnomobilizationofproteinfromtissues,reflectinganadequatesupplyofaminoacids.TheseresultsweresimilartothosereportedbyLammerset al.(2008)usingcrudeglycerin.

Even the levelsofglucoseandurea in thefinalcollectionwere higher than those in the initialcollection,andallvalueswerewithinthereferenceranges (85-150mg/dL and 21.4-64.2mg/dL forglucoseandurea,respectively;Duncanet al.,2003).Becausetheaverageureaandglucosecontentsdidnot differ acrossglycerin levels, it canbe inferredthatglycerinhadnoeffectontheseparameters,andthedifferencebetweenperiodsofcollectionresultedfromthephysiologicalresponsesofanimals.

Serumbiochemistry(noeffect)alongwithADWGandbodyweight(lineareffect)resultsofthisstudysuggests thatglycerinutilizationdoesnotmeet themaximumresponseingrowingpigs.Thismightbecorrect,becauseglycerinmetabolismisbasedonthefactthatglycerolfromthedietisabsorbedbypassivediffusion(Pluske,2007),isturnedintoglucoseintheliver via phosphorylation to glycerol-3-phosphate(Mourot et al.,1994),butanexcesswillbeexcretedintheurine(Oliveiraet al.,2014).Thisresultcouldbeindicativeofsaturationofthemetabolicpathwaysofglycerolduetothelimitationofglycerinconversiontoglycerine-3-phosphatebyglycerinkinase.However,Papadomichelakiset al. (2012)foundthatglycerolkinasemRNAexpressionintheliverofpigsincreasedlinearlywhenglycerinincreasedfrom0to15%inthedietduring42daysoffeeding,indicatingnosaturationeffect,whichpossiblyoccurredinthepresentstudy.

In conclusion, the additionof up to 15%semi-purified glycerin to the diet of growing pigsimprovedbodyweight,dailyweightgainandFGRwithoutaffectingserumlevelsofurea,triglycerides,cholesterol, and glucose.

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Acknowledgments

ThisresearchandthescholarshipofthefirstauthorweresupportedbyFundaçãodeAmparoàPesquisadoEstadodeMatoGrosso(FAPEMAT).FiagrilS.A.donatedthesemi-purifiedglycerinusedinthisstudy.

Conflicts of interest

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

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