Ileal and total tract apparent crude protein and amino acid digestibility of ensiled and dried cassava leaves and sweet potato vines in growing pigs

Ileal and total tract apparent crude protein and amino acid digestibility of ensiled and dried cassava leaves and sweet potato vines in growing pigs

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Animal Feed Science and Technology

journalhomepage:www.elsevier.com/locate/anifeedsci

aDepartment of Animal Nutrition and Biochemistry, Hue University of Agriculture and Forestry, 102 Phung Hung Street, Hue City, Viet Nam

bAnimal Nutrition Group, Department of Animal Sciences, Wageningen University, P.O Box 338, 6700 AH Wageningen, The Netherlands

cDepartment of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, P.O Box 80,151, 3508 TD Utrecht, The Netherlands

Article history:

Received 25 November 2009

Received in revised form

17 November 2011

Accepted 18 November 2011

Keywords:

Amino acid

Cassava leaves

Digestibility

Pigs

Sweet potato vines

© 2011 Elsevier B.V All rights reserved.

1 Introduction

Cassava(Manihot esculenta Crantz) andsweet potato(Ipomoea batatas L.)areimportantfood cropsinVietnam Cas-savaleavesarerelativelyrichincrudeprotein(CP,167–399g/kgDM),mineralsandvitamins(Eggum,1970;Phucetal.,

Abbreviations: AA, amino acids; CF, crude fibre; CIAD, coefficient of ileal apparent digestibility; CL, cassava leaves; CP, crude protein; CR, cassava root; CTTAD, coefficient of total tract apparent digestibility; DM, dry matter; HCN, hydrogen cyanide; aNDFom, neutral detergent fibre with a heat stable amylase and expressed exclusive of residual ash; OM, organic matter; SP, sweet potato; SPL, sweet potato leaves; SPV, sweet potato vines.

∗ Corresponding author Tel.: +84 54 6502 248; fax: +84 54 3524 923.

E-mail address:nguyenhoaly@gmail.com (T.H.L Nguyen).

0377-8401/$ – see front matter © 2011 Elsevier B.V All rights reserved.

172 T.H.L Nguyen et al / Animal Feed Science and Technology 172 (2012) 171– 179

2001;Montagnacetal.,2009)butalsocontainhighlevelsofcyanogenicglucosideswhichlimititsuseinanimalfeeding Sweetpotatovines(SPV)includeintheircompositiontheleaves(260–330gCP/kgDM)andstems(100–140gCP/kgDM) (Woolfe,1992;Ishidaetal.,2000;Anetal.,2003).TheuseofSPVinanimalfeedingislimitedbythehighcontentinoxalic acid(470±15mg/100gfreshweight),phyticacid(0.46±0.01mg/100gfreshweight),tannicacids(491±7mg/100gfresh weight)andtrypsin(52.0±0.9TIU/g)andchymotrypsin(69.1±0.6TIU/g)inhibitors(Moshaetal.,1995;Rekhaetal.,1999; HouandLin,1997).Cassavaleavesandsweetpotatoleaves(SPL)havebeenusedasaproteinsourceindietsforpigsin Vietnamand canreplacepartlyotherproteinsources(Phucetal.,2000;Phucand Lindberg,2001;VanAnetal.,2005) DryingandensilingareeffectivewaysofreducingtheHCNconcentrationsinCL(Borinetal.,2005;Cardosoetal.,2005; Wanapat,2009)andasaresultthesetechniquesareusedtoincreasethenutritionalvalue

Twostudieshavereportedthecoefficientofilealapparentdigestibility(CIAD)ofaminoacids(AA)forleavesingrowing pigs.PhucandLindberg(2001)reportedCIADofAAforCLmeal,ensiledCL,groundnutfoliageandleucaenawhenincluded (0.15g/gDM)inacassavarootandsoybeanmealbasaldietingrowingpigs.Anetal.(2004)investigatedeffectsofthe inclusionoffresh,dryandensiledSPL(notincludingstems)ontheCIADofAAingrowingpigsandfoundformostAAno differenceinCIAD.InVietnam,smallholderfarmscommonlyuseSPVormixturesofCLandSPVeitherdriedorensiled(Pham

etal.,2010)asadietaryingredientforpigsandoftendonotseparateleavesandstems.KnowledgeoftheCIADofAAin practicaldietsisimportantinordertoallowimprovementindietaryformulationforgrowingpigsandincreaseprofitability

tosmallholderfarmers

ThepresentstudywasconductedtodeterminetheilealandtotaltractapparentdigestibilityofCPandAAinensiledand driedcassavaleaves,sweetpotatovinesanda50:50mixtureonaDMbasisofcassavaleavesandsweetpotatovinesin growingpigs.Theeffectofpreservationmethod(ensilingvs.drying)andadditivenessofthetwosourcesusedinthe50:50 mixtureontheCIADofAAwereevaluated

2 Materialsandmethods

2.1 Pigs and housing

The protocolofthe experimentwas approved bythe ethical committeeof Hue University (HueCity,Vietnam) Six castratedF1crossbred(LargeWhite×MongCai)growingpigsofapproximately5monthsofage,withanaveragebody weightof60.2±1.0kgwereused.Thepigsweresurgicallyfittedwithpost-valveT-caecumcannulasforcollectionofileal digesta.ThecannulationfollowedtheproceduresasdescribedbyVanLeeuwenetal.(1991).Pigswerehousedindividually

ina2.0m×1.0m(length×width)penwithfreeaccesstowaterfromnippledrinkersthroughoutthetrial

2.2 Ensiling and drying of cassava leaves and sweet potato vines

Freshcassava(Manihot esculenta)leaveswereharvestedat90daysafterplantingbycuttingmaterialataheightof30cm

orabove.Harvestedmaterial(leaves+stems)wasthoroughlymixedandsampledbeforebeingwiltedfor5h.Thewilted materialwasdividedintotwoequalportionswithonehalfusedtocollecttheleaveswhichwerechopped(2–3cm)byhand Ricebran(50g/kg)andcommonsalt(5gNaCl/kg)wereaddedtothewiltedCLandthoroughlymixedbyhandbeforestorage

atambienttemperaturein30kgsealedairtightplasticbagsforatleast2monthsbeforebeingfedtothepigs.Theensiled

CLwasfedtopigsforlessthan6daysafteropeningofabag.Ahomogenoussample(500g)wascollectedfromeachbag directlyafteropening,stored(−20◦C)andsamplespooledbeforearepresentativesample(300g)wastakenforchemical analysis.Theotherhalfofthematerialwaslefttodryinthesunfor2–3days.Driedleaveswerecollected,milledovera

1mmscreen,andstoredinplasticbagsatambienttemperature.DriedCLsamples(200g)werecollectedrandomlyfrom eachbag,pooled,mixedhomogeneouslyandasample(300g)wasanalysedforDMandhydrogencyanide(HCN)content andstored(−20◦C)inairtightcontainersforfurtheranalysis

Sweetpotato(Ipomoea batatas)vineswereharvestedat60daysafterplanting,cutat10cmdistancefromthemainstems andchopped(2–3cm)byhand.Arepresentativesamplewasstoredbeforethematerialwaswiltedovernightanddivided intotwoequalparts.Onehalfwasmixedwithricebran(100g/kg)and5gNaCl/kgandstoredinsealedairtightplasticbags (30kg)andstoredfor>21daysbeforebeingfedtopigs.TheensiledSPVwasfedtopigsforamaximumof5daysafter openingabag.TheotherhalfoftheSPVwasdriedinthesunfor2–3daysbeforebeingmilledovera1mmscreen,and storedinplasticbags.TheprocedureofcollectingsamplesforchemicalanalysisofensiledordriedSPVwassimilartothat

ofensiledanddriedCL

2.3 Diets and experimental design

Sixexperimentaldiets wereformulatedbasedonensiledcassavarootsastheenergysource(Table1 In fourofthe experimentaldiets,driedCL,ensiledCL,driedSPVandensiledSPVwasthemainsourceofprotein(912–929gCP/kgdietary CP)withtheremainingproteinoriginatingfromtheensiledCR.Intheothertwodiets,proteinwassuppliedfroma50:50 mixtureonaDMbasisofCLandSPVindriedorensiledform.Lessthan90g/kgoftheCPoriginatedfromtheensiledcassava rootsinthevariousdiets.Thesixdietswereformulatedtocontainapproximately116gCP/kgDMwithsoybeanoiladded

Table 1

Chemical composition (g/kg DM unless otherwise stated) of the ingredients.

a All values were determined(n= 3) except for metabolisable energy which was calculated from NIAH (2001) data.

b Silage made from 945 g wilted cassava leaves, 50 g rice bran and 5 g NaCl/kg.

c Silage made from 895 g wilted sweet potato vines, 100 rice bran and 5 g NaCl/kg.

d Neutral detergent fibre with a heat stable amylase and expressed exclusive of residual ash.

e 1221 and 342 mg/kg DM in fresh cassava leaves and roots, respectively.

f ND, not determined.

Table 2

Ingredient and analysed chemical composition, calculated metabolisable energy content and hydrogen cyanide content of the experimental diets fed to growing pigs.

Cassava leaves Sweet potato vines Mixture a

Ingredient (g/kg DM)

Chemical composition (g/kg DM)

a Mixture (50:50 on a DM basis) of ensiled or dried cassava leaves and sweet potato vines.

b Ensiled with 50 g rice bran/kg wilted cassava leaves.

c Ensiled with 100 g rice bran/kg wilted sweet potato vines.

d Supplied per kg of diet: 12 mg retinol: 21.6 ␮g cholecalciferol, 75 mg ␣-tocopherol, 25 mg phytylmenaquinone, 10 mg thiamin; 75 mg riboflavin, 125 mg calcium pantothenate, 150 mg niacin, 0.15 mg cyanocobalamin, 10 mg folic acid, 0.5 mg choline, 0.5 mg Fe, 0.575 mg Zn, 0.2 mg Cu, 0.75 ␮g Co, 3.0 ␮g I and 1.5 ␮g Se.

e Neutral detergent fibre with a heat stable amylase and expressed exclusive of residual ash.

(30–40g/kg)toadjustthecalculatedmetabolisableenergy(ME)contentto12.5MJ/kgDM.DietaryMEwascalculatedusing theformulasandvaluesreportedbyNIAH(2001)forpigs.DietaryMEwascalculatedusingtheformula:

ME(kJ/kg)=(5.01X1+8.93X2+3.44X3+4.08X4)×4.184

whereX1–X4arethedigestibleprotein,digestiblefat,digestiblefibreanddigestiblenitrogen-freeextractivescontenting/kg feed.Chromiumoxidewasaddedasadigestaflowmarkerat5g/kg(Table2

Thesixexperimentaldietswerefedtopigsaccordingtoa6×6Latinsquaredesignwitheachperiodlasting12dayswith

5daysdietaryadaptationfollowedby4daysofcollectionoffaeces,onedayofcollectionofilealdigesta,onedayofrestand

aseconddayofilealdigestacollection.Thedailyfeedinglevel(3.0kg/100kgbodyweight)duringthecollectionperiodwas setslightlybelowthemaximumlevelconsumedduringtheadaptationperiodtoreducefeedresidues.Thepigswerefed twicedailyat6:00and18:00h,withthedailyallowanceequallydividedbetweenthetwomeals.Foodrefusalsandspillage werecollected,driedandusedtocalculatethefoodintakedata

174 T.H.L Nguyen et al / Animal Feed Science and Technology 172 (2012) 171– 179

2.4 Digesta, faeces collection and calculations

ForthedeterminationoftheCIAD,ilealchymewascollectedevery2hduringthe12hperiodbetweenthemorningand afternoonfeeding,givingsixsamplespercollectionday.Ateachsamplecollection,digestawerequantitativelycollected for1hincontainersthroughsoftplastictubingconnectedtotheilealcannula.Thedigestawerefrequentlyremovedfrom thetubeandcontainerandtransferredtoalargercontainerwhichwaskeptoniceduringtheentiresamplingprocedure beforedigestasampleswerefrozenat−18◦C.Faeceswerecollectedfourtimesperdayandstoredat−18◦C.Digestibility

ofadietarynutrient/componentateachsamplingsitewascalculatedusingthechromiumtechnique(Saueretal.,2000) accordingtotheequation:

CADD=1−

DCD ×

ID

IF



whereCADDisthecoefficientofapparentdigestibility(ilealortotaltract)ofadietarynutrient/component;DCFthedietary nutrient/componentconcentrationinilealdigestaorfaeces(g/kg);DCD thedietarynutrient/componentconcentrationin thediet(g/kg);IDthechromiumconcentrationinthediet(g/kg);IFthechromiumconcentrationinilealdigestaorfaeces (g/kg)

2.5 Chemical analyses

Priortochemicalanalyses,individualilealdigesta(2days,6collections/day)andfaeces(4days,4collections/day)samples werethawedandpooledperpigduringeachperiodbeforearepresentativesub-samplewastaken.Feed,digestaandfaecal samplesweredriedat45◦Cfor24handmilledovera1mmscreenbeforeanalyses.Nitrogencontentoffaecesanddigesta wasdeterminedinfreshsamples,whereastheanalysesofothercomponentsinfeeds,faecesanddigestaweredeterminedin driedsamples.Thechemicalcompositionwasdeterminedaccordingtostandardmethods(AOAC,1990)includingdrymatter (method930.15),ash(method942.05),CP(Nx6.25;method988.05)andcrudefibre(CF;method978.10).Etherextractwas determined afterextractionwithpetroleumetherbythe Soxhletmethod(method920.39).TheprocedureofVan Soest

etal.(1991)withadditionofsodiumsulphiteandalphaamylasewasusedtodetermineneutraldetergentfibre(aNDFom) Chromiumoxideinfeed,faecesandilealdigestawasdeterminedbyatomicabsorptionspectrometryafterashingaccording

toFentonandFenton(1979).AminoacidcontentwasanalysedaccordingtoSpackmanetal.(1958)onanion-exchange columnusinganHPLC.Briefly,sampleswerehydrolysedfor24hat110◦Cwith6MHClcontaining2g/lreagentgradephenol and5␮molnorleucine(internalstandard)inevacuatedandsealedignitiontubes.Methionine(Met)andcysteine(Cys)were determinedasMetsulphoneandcysteicacid,respectively,withseparatesampleshydrolysedfor24hasdescribedabove followingoxidationwithperformicacidovernightat0◦C.Hydrogencyanidecontentwasdeterminedonfresh,ensiledor driedsamplesbytitrationwithAgNO3afterboilingthesamplesandconcentratingtheHCNinKOH(AOAC,1990).Thefresh

CLandfreshSPVwereanalysedforDM,CP,AAandHCNcontent(excepttheSPV).Freshcassavarootswerealsoanalysed forDMandHCNcontent.Allsampleswereanalysedintriplicateexceptaminoacidswhichwereanalysedinduplicate

2.6 Statistical analysis

Dailyfeedintakedatawereaveragedperpigandperperiod.Datawereanalysedbyanalysisofvarianceaccordingtoa

6×6squarearrangementusingtheGeneralLinearModelprocedureof(SASInst.,Inc.,Cary,NC)usingthefollowingmodel:

Yij(k)=+Ti+Pj+Ak+eij(k)

whereYisadependentvariable,istheoverallmean,T ithetreatmenteffect(i=driedenensiledCL,SPVandCL+SPV),P j

theperiodeffect(j=1–6),Aktheeffectofanimal(k=1–6),e ij(k)istherandomerror.Tukeypair-wisecomparisonswereused

todeterminedifferencesbetweentreatmentmeans.Differencesbetweentheactualresultsofmixture(driedorensiled) andexpectedresultbasedonsingleingredients(i.e.0.5×resultforcassavaleaves+0.5×resultforsweetpotatovines)were testedforsignificanceusingtheCONTRASTstatement.Probabilitylevelwasseta5%

3 Results

3.1 Intake

TheCPandAAcontentwashigherintheCLingredientscomparedtothecorrespondingSPVingredientwiththeexception

ofThrandValinthefreshmaterial(Table3 TheCPandAAcontentintheensiledmaterialwerelowerthaninthedriedor freshmaterial.TheensiledCLandensiledSPVhadalowercontentofLys,His,Ile,Met+Cys,PheandThrthanfreshordried

CLandfreshSPV(Table3 Thecassavarootonlycontained17gCP/kgDM

ThedailyintakesofOM,CF,aNDFomandMEweredifferentamongdiets(P<0.001,Table4 Atrendwasobservedforthe dailyintakeofDM(P<0.071)andCP(P<0.071)amongdiets.ThelowestdailyDMintakewasrecordedforthedriedSPVdiet,

Table 3

Crude protein and amino acid composition (g/kg DM) of the cassava (roots and leaves) and sweet potato vines used in the experimental diets.

Ensiled Fresh Ensiled Dried

Methionine + cysteine 0.11 6.24 4.82 6.25 4.50 4.20 4.29

Aspartic acid 1.56 25.83 18.12 25.14 24.20 14.08 22.13 Glutamic acid 3.55 35.72 23.01 36.01 18.28 16.68 15.64

Table 4

Average daily intake of dietary components and metabolisable energy of the experimental diets by growing pigs.

Cassava leaves Sweet potato vines Mixture a Ensiled Dried Ensiled Dried Ensiled Dried

Calculated metabolisable energy (MJ/d) 19.2 ab 20.6 a 19.0 ab 18.1 b 18.3 ab 20.1 ab 0.6 0.031 Means within a row with no common letters (a, b, and c) differ (P<0.05).

a Mixture (50:50 on DM basis) of ensiled or dried cassava leaves and sweet potato vines.

b n= 6 with each sample obtained from a consecutive 4-day collection period.

c Neutral detergent fibre with a heat stable amylase and expressed exclusive of residual ash.

whilea12%higherintakewasfoundforthedriedCLdiet.TheCFandaNDFomintakeswerehigher(P<0.001)inthedried andensiledSPVdietscomparedtothecorrespondingCLdiets

3.2 Ileal and total tract apparent digestibility of nutrients

Thereweredifferences(P<0.05)inCIADandCTTADbetweendietsforDM,OM,CPandCF(Table5 Inaddition,CTTADof aNDFomwasdifferent(P<0.002)amongdiets.TheCIADofDM,OM,CPandCFwerenotdifferent(P>0.05)betweenensiled anddriedCL.TheCIADofDM,CPandCFwerehigher(P<0.05)intheensiledSPVcomparedtothedriedSPV.OnlytheCIADof

DMwasdifferent(P<0.05)betweentheensiledanddryCL+SPV.NodifferenceswereobservedbetweentheCTTADofDM,

OM,CP,CFandaNDFombetweentheensiledanddryCL+SPV.The50:50mixtureofCL+SPVgavehigher(P<0.05)CIADfor aNDFomthancalculatedbasedonindividualaNDFomCIADvaluesofCLandSPV.Non-additivityofindividualvalueswas alsofoundfortheCTTADofDMandOMforthedriedCL+SPVaswellasCFfortheensiledCL+SPV(Table5

TherewerestatisticallysignificantdifferencesintheCIADofCPandmostAAexceptMet+Cys,Glu,GlyandSerbetween diets(Table6 Althoughforprolinetherewasasignificantdieteffect(P<0.05),theTukeypair-wisecomparisontestdid notidentifydifferencesbetweentreatments.NoneoftheCIADofAAwasdifferentbetweentheensiledanddriedCL.Only theCIADofTyrandAspweredifferentbetweentheensiledanddriedSPV.OnlythelysineCIADwasdifferentbetweenthe ensiledanddriedCL+SPV.Significant(P<0.05)non-additiveeffectswereobservedfortheCIADofanumberofAAinthe ensiledanddriedCL+SPV.ForensiledCL+SPV,theCIADofHis,Lys,Thr,AspandProwashigherthantheexpectedaverage valueofamixtureofCL+SPV.ForthedriedCL+SPV,theCIADofHis,Leu,Thr,Tyr,Ala,AspandSershowednon-additivity

176 T.H.L Nguyen et al / Animal Feed Science and Technology 172 (2012) 171– 179

Table 5

Coefficients of ileal and total tract apparent digestibility of nutrients in the experimental diets fed to growing pigs.

Cassava leaves Sweet potato vines Mixture a Treatment Interaction b

Ileal apparent digestibility

Dry matter 0.697 bc 0.685 c 0.727 a 0.698 bc 0.717 ab 0.685 c 0.005 <0.001 0.458 0.325 Organic matter 0.737 ab 0.728 b 0.750 ab 0.742 ab 0.757 a 0.735 ab 0.005 0.012 0.052 1.000 Crude protein 0.468 abc 0.440 c 0.492 a 0.453 c 0.488 ab 0.457 bc 0.008 0.001 0.385 0.300 Crude fibre 0.255 ab 0.218 b 0.278 a 0.220 b 0.307 a 0.282 a 0.012 <0.001 0.012 <0.001 Total tract apparent digestibility

Dry matter 0.762 ab 0.730 b 0.772 a 0.733 b 0.772 a 0.753 ab 0.008 0.003 0.619 0.041 Organic matter 0.787 ab 0.762 b 0.797 a 0.770 ab 0.798 a 0.800 a 0.006 0.002 0.435 0.001 Crude protein 0.572 ab 0.523 c 0.572 ab 0.542 bc 0.578 a 0.545 abc 0.008 <0.001 0.486 0.198 Crude fibre 0.393 b 0.380 b 0.452 a 0.418 ab 0.467 a 0.428 ab 0.013 0.001 0.012 0.082 aNDFom d 0.333 bc 0.307 c 0.400 a 0.365 abc 0.395 ab 0.370 abc 0.015 0.002 0.137 0.076 Difference between total tract and ileal apparent digestibility

Dry matter 0.065 a 0.045 ab 0.045 ab 0.035 b 0.055 ab 0.068 a 0.006 0.008 1.000 0.001 Organic matter 0.050 ab 0.033 bc 0.047 abc 0.028 c 0.042 bc 0.065 a 0.005 <0.001 0.265 <0.001

Crude fibre 0.138 b 0.162 ab 0.173 ab 0.198 a 0.160 ab 0.147 b 0.010 0.004 0.726 0.010 Means within a row with no common letters (a, b, and c) differ (P<0.05) d Neutral detergent fibre with a heat stable amylase and expressed exclusive of residual ash.

a Mixture (50:50 on a DM basis) of ensiled or dried cassava leaves and sweet potato vines.

b Difference of mixture from 0.5 × mean of cassava leaves + 0.5 × mean of sweet potato vines.

cn= 6.

d Neutral detergent fibre with a heat stable amylase and expressed exclusive of residual ash.

Table 6

Coefficient of ileal apparent digestibility of amino acids of the experimental diets fed to growing pigs.

Cassava leaves Sweet potato vines Mixture a Treatment Interaction b

Arginine 0.528 b 0.520 b 0.630 a 0.573 ab 0.565 a,b 0.565 a,b 0.022 0.033 0.621 0.513 Histidine 0.694 ab 0.690 b 0.695 ab 0.680 b 0.747 a* 0.728 a,b* 0.013 0.008 0.003 0.010 Isoleucine 0.648 b 0.653 ab 0.755 a 0.755 a 0.755 a 0.750 a,b 0.024 0.004 0.084 0.134 Leucine 0.674 b 0.650 b 0.790 a 0.762 a 0.763 a 0.760 a* 0.014 <0.001 0.088 0.006 Lysine 0.697 ab 0.683 b 0.718 ab 0.670 b 0.792 a* 0.692 b 0.022 0.010 0.005 0.578 Methionine + cysteine 0.706 0.712 0.737 0.695 0.715 0.715 0.010 0.170 0.614 0.369 Phenylalanine 0.584 c 0.613 bc 0.740 a 0.653 abc 0.680 a,b 0.673 abc 0.022 0.001 0.372 0.154 Threonine 0.657 bc 0.630 c 0.748 a 0.712 a,b 0.750 a* 0.715 ab* 0.017 <0.001 0.035 0.049 Tyrosine 0.736 c 0.758 bc 0.877 a 0.653 d 0.838 a 0.830 ab* 0.018 <0.001 0.156 <0.001

Alanine 0.721 bc 0.682 c 0.807 a 0.762 a,b 0.777 ab 0.757 ab* 0.014 <0.001 0.452 0.048 Aspartic acid 0.669 b 0.700 b 0.678 b 0.793 a 0.767 a* 0.788 a* 0.014 <0.001 <0.001 0.024

Means within a row with no common letter (a, b, c and d) differ (P<0.05).

a Mixture (50:50 on a DM basis) of ensiled or dried cassava leaves and sweet potato vines.

b Difference of mixture from 0.5 × mean of cassava leaves + 0.5 × mean of sweet potato vines.

cn= 6.

4 Discussion

TheCPcontentsoftheCLandSPVusedinthepresentstudywereingoodagreementwithreportsintheliterature(Dung

etal.,2002;Montagnacetal.,2009;Woolfe,1992).ThelowerCPcontentoftheensiledCLandSPVcomparedtothedried materialisalsoinagreementwiththestudiesofPhucandLindberg(2000,2001)onprocessedCL.Theensiledproducts containedapproximately5%lessCPthanthedriedproducts.Thiscanpartlybeexplainedbytheadditionofthericebranto thewiltedcassavamaterialtofacilitatetheensilingprocess.Ricebrancontains110gCP/kgDMcomparedtothe299and

223gCP/kgDMinthefreshCLandSPVandthereforericebranadditiondilutestheconcentrationofCPoftheleaves/vines ThereductioninCPcontentinCLorSPVsilagemayalsohavebeenduetonitrogenlossesfromproteindecomposition Bothdryingandensilingreducedtheconcentrationofanti-nutritionalfactorsofCLandSPV.TheHCNcontentofthe freshCLwasfoundtobe1,221mg/kgDMandwasreducedto128mg/kgDMafter60daysensilingand152mg/kgDMafter

Fig 1 Relative concentration of individual essential amino acids in the six protein sources (CL = cassava leaves; SPV = sweat potato vines) in meeting the amino acid requirements of 50–80 kg growing pigs ( NRC, 1998 ) Values adjusted for energy density of the diet.

sun-drying.TheHCNcontentoffreshcassavarootswas342mg/kgDMwhichwasalsoreducedbyensilingto20mg/kgDM after60days.TheHCNcontentoftheensiledCL(78mg/kgDM)anddriedCL(58mg/kgDM)dietswashigherthaninthe othertreatments.NoindicationsofcyanidetoxicitywereobservedinanyofthepigsfedthedietscontainingHCNinthe presentstudy.Inanimals,thelethaldoseofHCNisgenerallyreportedtobebetween0.66and15mg/kgbodyweightfor variousspecies(WHO,1965;FSANZ,2005).Tewe(1992)reportedatoxicitylevelofHCNforpigsof3.5mg/kgbodyweight

Inthepresentstudy,pigsfedtheensiledanddriedCLingestedapproximately2.0and1.6mgHCNperkgbodyweightor abouthalfofthereportedlevelswhichareconsideredtoxic

Astheensiledmaterialusedinthepresentstudycontainedricebraninordertoimprovetheensilingprocess,direct comparisonbetweenthedriedandensiledproductsaredifficult.Itshouldbenotedthattheilealdigestasamplesweredried

at60◦C.Althoughunlikely,somemicrobialgrowthmayhaveoccurredwhenthesamplewasheatedtothistemperature andchangesintheAAcompositionmayhaveoccurredduringthistimeduetobacterialfermentation.TheAAcomposition

oftheCLandSPVinthepresentstudy,however,isingoodagreementwithearlierreports(Eggum,1970;Ravindran,1993; PhucandLindberg,2001;Montagnacetal.,2009;Woolfe,1992;Kinh,2003).Althoughtheproteininthedietsoriginated fromthreedifferentingredients(CL/SPV,ricebranandECR)withtheCPoftheCL/SPVmakingupmorethan75.4–93.9%

ofthetotalCP,theCIADforlysineandthesulphuraminoacidsreportedhereforthedietsareincloseagreementwith thecalculatedCIADvaluesoftheCL/SPV.Fig.1showstherelativeconcentrationofindividualessentialAAinthesixdiets investigatedinthepresentstudyinmeetingtheAArequirementsofgrowingpigs(NRC,1998)whenvaluesarecorrected fortheenergydensityofthediet.Met+CyswerefoundtobethemostlimitingAAinallthesixdietstested,closelyfollowed

bylysine.ComparedtotheAArequirementestimatesof50–80kgpig(NRC,1998)withahigh-mediumleangrowthrate (325g/dayofcarcassfat-freelean),theilealdigestibleMet+CyscontentoftheensiledanddriedCL,ensiledanddriedSPV andensiledanddriedCL+SPVdietsonlymet36,38,45,33,36and37%oftherequirementsforgrowth,respectively.Eggum (1970)andPhucetal.(2000)reportedthattheconcentrationofthesulphur-containingAAwasratherlowinCL.Recently,

Chauynarongetal.(2009)andMontagnacetal.(2009)alsofoundthatthemostlimitingAAinCLisMet.Thesedataarein contrasttoreportsofWoolfe(1992)andAnetal.(2003)whofoundthatLyswasthefirstlimitingAAinfreshSPL.Thesecond mostlimitingAAinthesixdietsinthepresentstudywasLys,meeting53,48,49,40,51and50%oftherequirementsof growingpigs(NRC,1998).OnlyarginineispresentinexcessamountswhileIlemeetstherequirementsleantypegrowing pigs(Fig.1 SupplementationofdietscontainingdriedandensiledCL,SPVora50:50mixtureonaDMbasisofCL+SPVas thesoleproteinssourcewithsulphurcontainingAAandLyscanbeexpectedtoincreaseproteinutilisationbygrowingpigs Non-additivitywasobservedforanumberofAAintheensiledanddriedCL+SPV.TheilealdigestibleLyscontentof theensiledmixturedietwas10.4%unitshigherthancanbeexpectedfromtheCIADdataofthetwoindividualingredients (ensiledCLandSPV)assumingadditivityofdigestibilityvalues.Similarly,assumingadditivity,thedriedCL+SPVdietresulted

inhigherthanexpectedCIADofLeu,ThrandHisthanbasedontheCIADoftheseAAfromtheindividualdriedCLandSPV

ItcanthereforebeexpectedthatadietcomposedofamixtureofCLandSPVwillresultinahighergrowthperformanceof pigswhensupplementedwithsulphuraminoacidastheilealdigestibleLyscontentwasthehighest(0.42g/kgDM)ofall thesixdiets

OurstudyshowedthattheCTTADwashigherthantheCIADforDM,OMand CFandatrendwasobservedfrom CP

In particular,the CTTADofCFwas0.14–0.20higherindicatingthat significantfermentationof CFoccurredinthelarge

178 T.H.L Nguyen et al / Animal Feed Science and Technology 172 (2012) 171– 179

intestineofthegrowingpigs.TherewasanetnitrogendisappearancefromthelargeintestineresultinginahigherCTTAD forCP.Thecontributionoffermentedcarbohydratetotheenergysupplyoftheanimalcanbeexpectedtobeabout70%of thatofenzymaticallydigestedstarch(CVB,1999).OurdataaresimilartostudiesbyAnetal.(2004)andPhucetal.(2000)

investigatingensiledandsundriedcassavaleaves,fresh,driedandensiledsweetpotatoleaves,andgroundnutfoliage.Dung

etal.(2002)reportedthatthecapacityofthepigtodigestandutilizefibreisaffectedbythefibresource.ThefibreindriedCL andensiledCLaswellasdriedSPVandensiledSPVappearstobewellfermentedbythemicroflorainthelargeintestineof pigs.The13–20%higherCTTADoffibreinthelargeintestineofpigsfoundinthepresentstudywillyieldadditionalenergy

intheformofvolatilefattyacidsandtherebymeetpartoftheenergyrequirementsofthepig

5 Conclusion

Ingeneral,sweatpotatovineshaveahighernutrientdigestibilitycomparedtocassavaleaveseitherdriedorensiled andensilingresultedinahigherdigestibilityofdietarynutrientscomparedtodrying.Hydrogencyanideconcentrationof cassavaleavesisreducedbybothensilinganddryingwithdryingbeingslightlymoreeffective.Also,contentofaminoacids

incassavaleavesandsweatpotatovinescanbeaffectedbythepreservationprocess,whichneedstobeaccountedforin dietformulation.Mixingensiledcassavaleavesandensiledsweatpotatovinesmayyieldadditionalbenefitsintermsof increaseddigestibilityofaminoacidsinpigscomparedtofeedingtheseingredientssolely.Thefirstlimitingaminoacids

inpracticaldietsformulatedfromdriedorensiledcassavaleavesaremethionine+cysteineandlysine.Providingdietary ingredientshighindigestiblemethionine,cysteineandlysineorprovisionoftheseaminoacidsincrystallineformindiets containingcassavaleavesandsweatpotatovinesmayincreaseaminoacidutilisationofthesedietsforpigs

Acknowledgements

Financial support from the Swedish International Development Cooperation Agency, Department for Research Co-operation(Sida-SAREC).MEKARNSida/SARECprogramforsupportingthisresearch.Profs.R.B.OgleandT.R Prestonfor theirhelpandvaluableadvice Dr.T.K.DoanoftheNationalInstituteofAnimalHusbandryinHanoiforperformingthe chemicalandaminoacidanalyses

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