Starch in ruminant diets: A review

Abstract

Background:
starch is an important energy source for ruminants nutrition. This carbohydrate is often used to improve rumen fermentation, optimizing digestion of structural carbohydrates and increasing protein flow to the small intestine. Microbial and digestive enzymes are involved in starch digestion, generating products that can positively or negatively affect animal performance and health, depending on the starch contents of the diet.

Objective:
to describe the basic characteristics of starches, the factors affecting its nutritional availability, and its effects in ruminants.

Conclusion:
a number of factors affect starch digestibility, including granule size, amylose/amylopectin ratio, proportion of farinaceous and vitreous endosperm, presence of starch-lipid and starch-protein complexes, and physical-chemical processing of the feed. Ingestion of large amounts of starch can trigger ruminal acidosis. However, its rational use in the diet has positive effects on methane emissions, and in milk yield and composition.

Full text

Rev Colomb Cienc Pecu 2016; 29:77-90
Revista Colombiana de Ciencias Pecuarias
Original articles
77
Literature Review
Starch in ruminant diets: a review¤
Almidones en la alimentación de rumiantes: revisión de literatura
Amido na alimentação dos ruminantes: revisão de literatura
Luis M Gómez1,2,3*, MVZ, MSc, (c)Dr. Sc; Sandra L Posada2, Zoot, MSc, Dr. Sc; Martha Olivera3, MV, Dr. Sc.
1Departamento de Investigación y Desarrollo, Grupo Nutri-Solla, Solla S.A., AA 1272, Itagui, Colombia.
2GRICA Research Group, Facultad de Ciencias Agrarias, Universidad de Antioquia, AA 1226, Medellín, Colombia.
3BIOGENESIS Research Group, Facultad de Ciencias Agrarias, Universidad de Antioquia, AA 1226, Medellín, Colombia.
(Received: April 15, 2015; accepted: November 11, 2015)
doi: 10.17533/udea.rccp.v29n2a01
¤ Tocitethisarticle:GómezLM,PosadaSL,OliveraM.Starchinruminantdiets:areview.RevColombCiencPecu2016;29:77-90.
* Correspondingauthor: LuisM Gómez.Director ofResearch andDevelopment, SollaS.A. Company.Carrera42 No.33-80 Itagui,Colombia. Tel+574
4448411.E-mail:lmgomezo@solla.com
Summary
Background:starchisanimportantenergysourceforruminantsnutrition.Thiscarbohydrateisoftenused
toimproverumenfermentation,optimizingdigestionofstructuralcarbohydratesandincreasingproteinow
tothesmallintestine.Microbialanddigestiveenzymesareinvolvedinstarchdigestion,generatingproducts
thatcanpositivelyornegativelyaffectanimalperformanceandhealth,dependingonthestarchcontentsofthe
diet. Objective: todescribethebasiccharacteristicsofstarches,thefactorsaffectingitsnutritionalavailability,
anditseffectsinruminants.Conclusion:anumberoffactorsaffectstarchdigestibility,includinggranulesize,
amylose/amylopectinratio,proportionoffarinaceousandvitreous endosperm,presence ofstarch-lipidand
starch-proteincomplexes,andphysical-chemicalprocessingofthefeed.Ingestionoflargeamountsofstarch
cantriggerruminalacidosis.However,itsrationaluseinthediethaspositiveeffectsonmethaneemissions,
andinmilkyieldandcomposition.
Keywords: acidosis, amylopectin, amylose, digestibility, lactation, methanogenesis.
Resumen
Antecedentes: el almidónes unimportante recursoenergético parala alimentaciónde rumiantes.Este
carbohidratoesfrecuentementeempleadoparaelmejoramientodelosparámetrosdefermentaciónruminal,
loqueoptimiza elaprovechamiento de loscarbohidratos estructurales eincrementa elujode proteínaal
intestinodelgado.Ensudigestiónparticipanenzimasmicrobianasydigestivas,lascualesgenerandiferentes

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Gómez LM et al. Starch in ruminant diets: a review
productosqueimpactanpositivaonegativamenteeldesempeñoproductivoylasaluddelanimal,dependiendo
del nivel de almidón en la dieta. Objetivo: describirlascaracterísticasbásicasdelosalmidones,losfactores
queafectansudisponibilidadnutricionalylosefectosdesuutilizaciónenlaalimentacióndelosrumiantes.
Conclusión:existeunsinnúmerodefactoresqueafectanladigestibilidaddelalmidón,entreellos,eltamaño
delgránulo,la relaciónamilosa/amilopéctina,laproporcióndeendospermofarináceoyvítreo,lapresencia
decomplejosconlípidosyproteínas,ysuprocesamientofísico-químico.Laingestióndegrandescantidades
dealmidónpuededesencadenaracidosisruminal;noobstante,suempleoracionalenladietadelosrumiantes
tieneefectospositivossobrelaemisióndemetano,ylaproducciónycalidaddelaleche.
Palabras clave: acidosis, amilopectina, amilosa, digestibilidad, lactancia, metanogénesis.
Resumo
Antecedentes: oamidoéuma importantefonte deenergianaalimentaçãodos ruminantes.Este carboidrato
é geralmente utilizado para melhorar os parâmetros de fermentação no rúmen, o que otimiza a utilização dos
carboidratosestruturaiseaumentao uxodeproteínaparao intestinodelgadodoanimal.Nasuadigestãoestão
envolvidas enzimas digestivas e microbianas, as quais geram diferentes produtos que impactam positiva ou
negativamenteodesempenhoprodutivoe asaúdedoanimaldependendo doníveldeamidona dieta.Objetivo:
descreverascaracterísticasbásicasdoamido,factoresqueafectamasuadisponibilidadenutricionaleosefeitosdasua
utilizaçãonaalimentaçãoderuminantes.Conclusão: diversosfatoresafetamadigestibilidadedoamido,incluindo
otamanhodogrânulo,arelaçãoamilose/amilopectina,aproporçãodeendospermafarináceoevítreo,aformação
decomplexoscomlipídeoseproteínaseoseuprocessamentofísico-químico.Aingestãodegrandesquantidades
deamidopodeprovocaracidoseruminal,noentanto,asuautilizaçãoracionalnaalimentaçãoderuminantestem
efeitospositivossobreasemissõesdemetano,aproduçãodeleiteeasuaqualidadecomposicional.
Palavras chave:acidose, amilopectina, amilose, digestibilidade, lactação, metanogênese.
Introduction
Starch–thelargestreservoirofplantpolysaccharides-
playsanimportantroleingerminationandgrowth,
anditssynthesisissecondonlytothatofcellulose.
Starchisthemainenergycomponentusedinruminant
feeds due to its availability (Ortega and Mendoza,
2003). It is often included in the diet to improve
ruminal fermentation, allowing for a better use of
structuralcarbohydratesandtoincreaseproteinow
tothesmallintestine(Huntingtonet al.,2006).Starch
sourcesare expensive,sotheymustbeusedwisely
tobecost-effective.Itisimportanttounderstandthe
structural characteristics of starch, its ruminal and
post-ruminal digestion and the factors affecting its
digestibility in order to improve performance and
prot of livestock systems. This review describes
starch,thefactorsaffectingitsnutritionalavailability,
anditseffectsinruminantfeedingandnutrition.
Description of starch
Composition
Starches are mainly α-glucans composed of
two types of molecules: amylose and amylopectin
(SantanaandMeireles,2014;Table1).Amyloseisa
linearD-glucosepolymercontainingabout99%α-1,4
links(Parker andRing,2001).Amylopectin,which
has95%α-1,4linksand5%α-1,6links(Stevneboet
al.,2006),isthemostabundantcomponentofstarches
(Figure 1). On the other hand, amylose content in
starchusuallyuctuatesfrom200to300g/Kg.Some
starch-richfeedssuchaswaxycerealsusuallycontain
negligibleamountsofamylose,whilehigh-amylose
sourcesmaycontainupto700gamylose/Kg.Cereals
suchaswheat,maize,barley,andricecancontaina
waxygenederivedfromnaturalmutationsofgenes
encoding granule bound starch synthase, which is
requiredforamylosesynthesis(Svihuset al.,2005).
Structure
Starchgranulesareformedbyconcentricallygrowing
layersalternatingsemi-crystallineandamorphouslms
(Figure1).Thesemi-crystallineregionismoreabundant
in amylopectin and is more impervious to enzymatic
attackbecauseofits resistance to entryofwater.The
amorphous region is rich in amylose and has lower
densitythanthecrystallinearea,whichfacilitateswater
ow and enzyme attack; however, it is abundant in
hydrogenbonds(Perezet al., 2009).

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Table 1. Properties of starch components.
Characteristic Component
Amylose Amylopectin
General structure Linear Branched
Branch sites Nonea1 per 20 to 25 glucose units
Polymerization degreeb
Molecular weight
~1.000
1 x 105-1 x 106 g/mol
~10.000-100.000
1 x 107-1 x 109 g/mol
Stability in solution Low High
a There is a type of branched amylose with 1 or 2 α-1,6 links per molecule.
b Number of glucose residues per molecule.
Adapted from Parker and Ring, 2001.
Figure 1. (A) Structure of starch granules, represented by organized laminar forms. Amorphous rings (composed mainly of amylose)
separate layers in the semi-crystalline regions (composed primarily of amylopectin). Modied from Perez et al., 2009. (B) Amylopectin
structure according with the cluster model by Myers et al., 2000. Glucan chains are depicted by solid lines while intersections between
them indicate branch linkages. The dotted lines show the limit of amylopectin side chain clusters with unbranched chains associated in
tightly packed double helices. a) depicts the amorphous areas separating amylopectin side chain clusters.
A
B

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Structural alterations
Gelatinization. It is the permanent alteration
of the granule structure by breaking its hydrogen
bonds. Starch absorbs water during gelatinization,
theexpansionbreaks the hydrogenbondsreleasing
someoftheamylosebyleaching,thusbirefringence
is reduced and starch becomes more soluble
and exposed to enzyme activity (Rooney and
Pugfelder,1986).Inexcessofwater,moststarches
gelatinise at temperatures higher than 80 °C. The
gelatinisationtemperatureishigherforsmallstarch
granules. Amylose-rich cereals are more resistant
togelatinisationthancereals with normal andhigh
amylopectin levels (Svihus et al., 2005). Table 2
shows gelatinization values for several foods and
processing methods. The degree of gelatinization
is higher for extruded vs. pelleted food since the
temperatureusedintheprocessishigher(upto250°C
vs.60-95°C;Caballero,2010).
Table 2. Starch gelatinization under several processing methods
in various feeds.
Food Gelatinization (%)1Processing
Corn 17.06 Unprocessed
Sorghum 12.47 Unprocessed
Yucca 7.59 Unprocessed
Concentrate 1 32.49 Pelleting
Concentrate 2 32.55 Pelleting
Concentrate 3 31.92 Pelleting
Corn 79. 3 Extruded
1Assessed by an enzymatic method (Medel et al., 1999).
Retrogradation. It is dened as the reversible
returnofasolubilized,dispersedoramorphousstate
toacrystallineorinsolubleform,whichlimitsstarch
digestibility. Amylose is the main component that
facilitatesretrogradation(Biliaderis,2009).
Sources of starch
Cereal grains and roots
Cerealgrainsare a major source of starch used
inanimalfeeds.Cereals are composed ofpericarp,
endosperm and germ (Figure 2). The pericarp
comprises3to8%ofthekernelweight,althoughit
canbeupto 25% in oats(Everset al.,1999).It is
mostlycomposed(90%)ofhighlyligniedberand
thestarchcontentislessthan10%(Liet al.,2007),
thuspericarpdigestibilitydoesnotexceed40%(Van
Barneveld,1999).
Figure 2.Corn kernel composition.Adapted from Eckhoff
andWatson(2009).
Theendospermrepresentsbetween60and90%of
thegrain.Itisthemorphologicalstructurecontaining
the starch. It also contains proteins, phospholipids
andash,butlittleneutraldetergentber(NDF)and
phosphorus (P; Eckhoff and Watson, 2009). The
endospermlayers,fromtheoutsidein,arealeurone,
peripheralendosperm,horny(orvitreous)andoury.
Boththeperipheraland the horny endospermhave
starch granules surrounded by a matrix abundant
in hydrophobic proteins called prolamines and
non-starch polysaccharides (PNAs; β-glucans,
arabinoxylans, and pectins), which are relatively
impermeabletowaterandenzymaticactivity(Zeoula
andCaldasNeto,2001;Giubertiet al.,2014).Grains
exhibitinghighproportion of peripheral and horny
endospermarecalledvitreousorhorny,whilethose
abundantinoury endosperm arecalledopaqueor
soft(ZeoulaandCaldasNeto,2001).
Non-conventional sources
Starchrepresentsanimportant fraction in many
crops.Mostcereals(i.e.corn, wheat, rice, oat, and
barley) contain between 60 and 80% starch, while
legumes (chickpea, bean, pea) contain from 25 to

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50%, tubers (potato, cassava, cocoyam, arrowroot)
from 60 to 90%, and some green fruit (banana,
mango) contain as much as 70% (Santana and
Meireles,2014).Asincereals,thelargestproportion
ofstarchcorrespondstoamylopectinandthesmallest
to amylose (17-30%; Hu et al., 2010). Amylose
represents14to19%ofstarchincassava,between2
and22%inpotato,andapproximately37%inplantain
(Knowleset al.,2012).Amylopectininstarchfrom
potatoislessbranchedcomparedtocereals(Alvani
et al.,2011).Itisalsohighlyexpandable(Vasanthan
andBhatty,1996) and gelatinizes atrelatively low
temperature(between64.4 and 69.9 °C) compared
tootherstarches(Hernandez-Medinaet al.,2008).
Table3showsamyloseandamylopectinconcentration
indifferentstarchyfoodsandconcentratesfedtodairy
cattle.Differencesinamylose/amylopectinratioaffect
therateofruminalorintestinaldigestion.Digestionrate
ofamylopectinis usuallyhigherthanthat of amylose
(Knowleset al.,2012).
Tab le 3. Amylose and amylopectin content in various feeds.
Source Amylose (%) Amylopectin (%)
Corn 29.24 70.76
Sorghum 29.55 70.45
Yucca 19.84 80.16
Concentrate 1 (C1)* 21.17 78.83
Concentrate 2 (C2) 22.22 77.78
Concentrate 3 (C3) 20.25 79.75
Concentrate 4 (C4) 24.89 75.10
*Isoenergetic and isoproteic concentrates (C) for dairy cattle formulated
with four carbohydrate sources: corn (C1), sorghum (C2), yucca (C3), citrus
pulp (C4). Assessed using the method described by Gibson et al. (1997).
Ruminal and post-ruminal digestion of starch
Once it reaches the rumen, starch is degraded
mainly by amylolytic bacteria and by fungi and
protozoato alesserextent(Huntington,1997).The
α-1-4andα-1-6endoandexoamylasesproducedby
rumenmicroorganismshavetheabilitytohydrolyze
amylose and amylopectin glycosidic linkages,
releasingdifferentoligosaccharides(Table4).
The post-ruminal process of starch degradation
begins with pancreatic α-amylase secretion, which
hydrolyzes amylose and amylopectin into dextrins
andlinearoligosaccharideswithtwotothreeglucose
units. The process is completed by the action of
oligosaccharidases(maltaseandisomaltase)secretedin
theintestinalmembrane(OrtegaandMendoza,2003).
Inruminants,thesite of starchdigestionaffects
thesubstratesabsorbed.Ruminaldigestiongenerates
volatilefattyacids(VFA)forabsorptionandprovides
energyformicrobialproteinsynthesis(Huhtanenand
Sveinbjörnsson,2006). Decreasedrumendigestibility
ofstarchisdesirabletopreventfromacidosisandto
increasethesupplyofglycogenicsubstrates(Svihus
et al.,2005). Starchdigestioninthesmallintestine
implies greater energetic efciency compared with
ruminaldigestionduetoreducedmethaneproduction
and fermentation heat losses and higher efciency
of metabolisable energy utilisation (Huhtanen and
Sveinbjörnsson, 2006). Nevertheless, the increased
energyefciencyfromhigherstarchdigestioninthe
small intestine is offset by the increase in hindgut
fermentation,becauseonlyVFAareabsorbedfrom
thehindgutwhereasmicrobialmatterisexcretedin
feces.Adecrease inruminalstarchdigestion isnot
associated with an increase in its small intestinal
Table 4. Enzymes involved in starch hydrolysis.
Enzyme Link End product
Phosphorylase α -1-4 glycosyl Glucose 1 phosphate
Alpha-amylase α -1-4 glycosyl Linear and branched oligosaccharides
Beta-amylase α -1-4 glycosyl Maltose and limit dextrins
Amyloglucosidase α -1-4 glycosyl and α -1-6 glycosyl Glucose
Isoamylase α -1-6 glycosyl Lineal chains of α -1-4 glucans
Pullulanase α -1-6 glycosyl Lineal chains of α -1-4 glucans
Adapted from Tester et al., 2004.

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Gómez LM et al. Starch in ruminant diets: a review
digestion,butitisassociatedwithhigherhindgutand
lowertotaltractdigestibility(Larsenet al.,2009).
Forthisreason,rumenisconsideredtheprimary
site of starch digestion. Ruminal digestion usually
accountsfor 75to80% oftheintake, andabout35
to60%ofthestarch entering the small intestine is
degraded.About35to50%ofthestarchthatescapes
digestion in the small intestine is degraded in the
hindgut(Harson,2009).Accordingtoameta-analysis
byMoharreryet al.(2014),ruminalstarchdigestibility
variesgreatly(from 224to942 g/Kg).Theauthors
alsonotedthatstarchconsumptionadverselyaffected
ruminalstarchdigestibility,obtaininganegativeslope
of1.4%perKgincreaseindailystarchintake.Table
5 presents the content and ruminal digestibility of
various starch sources used in livestock.
Table 5. Starch content and ruminal digestibility of several starch
sources commonly used as feed supplements in dairy cattle.
Grain Starch (%) Rumen digestibility (%)a
Corn1,2 76.0 72 - 89.9
Sorghum1,2 71.3 60 - 78.4
Wheat1,2 70.3 88.3 - 88.1
Barley1,2 64.3 80.7 - 84.6
Oats1,258.1 92.7 - 94.0
Yucca380.0 91.0
a Variability is explained by grain treatment (grinding, rolling, aking).
1 Herrera-Saldana et al., 1990. 2Huntington, 1997. 3Vearsilp and Mikled, 2001.
Factors affecting starch digestibility
Granule size
Thisisalimitingfactorinstarchdigestionbecause
therelationship betweenstarchvolumeandsurface
area,andthussubstrate-enzymecontact,decreasesas
granulesizeincreases(Sviluset al.,2005).Cereals
withsmallgranules,suchasoatsandrice,aremore
digestiblethancorn, wheat andpotato,whichhave
longgranules(Bednaret al.,2001;Sviluset al.,2005).
Amylose/amylopectin ratio
Several studies have shown that amylose/
amylopectinratioisnegativelycorrelatedwithstarch
digestion(Bednaret al.,2001).Amyloseisinserted
intoamylopectinmoleculesincreasingtheamountof
hydrogen bonds within the starch molecule, which
negatively impacts the ability of expansion and
enzymeactivity(Caldas-Netoet al., 2000).Likewise,
starchgranuleswithhighamylosecontentaremore
pronetoretrogradation(Sviluset al.,2005).
Floury versus vitreous endosperm
Severalresearchers(Correaet al.,2002;Ngonyamo-
Majeeet al.,2008)havereportedaninverserelationship
betweenstarch digestibilityandvitreousness.Allen
et al.(2008),studiedruminalandduodenal-stulated
cows using corn with vitreous endosperm content
varyingbetween25and66%.Theyfoundthatfeeding
cornwith66%ofvitreousendospermreducedruminal
digestionin19.1%andoveralldigestionin7.1%.
Starch-lipid complexes
Quantitatively,lipids are the major non-starch
compoundsinstarchgranulesandcanbefoundas
freefattyacids(mostly palmiticandlinoleicacid)
and lysophospholipids (Svihus et al., 2005). In
cereal grains, a portion of amylose has insoluble
starch-lipidcomplexes,whichformhelicalstructures
that provide greater adhesion between molecules,
dininish starch swelling (Vasanthan and Bhatty,
1996), decrease their solubility (Rooney and
Pugfelder,1986)andreducetherateofenzymatic
digestion(Croweet al., 2000).Cassavaandpotato
starch contain a smaller percentage of lipids
compared with cereal starch (Zeoula and Caldas
Neto,2001;Alvaniet al.,2011).
Starch-protein complexes
The proteinaceous matrix surrounding starch
granulesaffectsstarchdigestibility.Digestibilityis
negativelyassociatedwiththepresenceofprolamins.
Prolaminsarestorageproteinsthatreceiveadifferent
nameforeach cereal,namelyzein(corn), karins
(sorghum), gliadin (wheat), hordeins (barley),
secalins(rice),andavenines(oats).Usually,wheat,
oats, rice and barley have fewer prolamins than
cornand sorghum(Momanyet al.,2006; Giuberti
et al.,2014).

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Zeinsaccountfor50to60%oftheproteininthe
wholegrainand are locatedattheperiphery of the
cell.Flouryendospermislowinzeincomparedwith
vitreous endosperm (Giuberti et al., 2014). Zeins
arenotsolubleintherumenenvironment(Lawton,
2002).Starchdigestionrequiresthatrumenbacteria
degradezeinsrstviaproteolysis,beforestartingthe
amylolyticactivity(Cotta,1998).
Processing of cereal grains
Grain processing using temperature, humidity
andpressurefacilitatebinding of bacteria tostarch
granules,increasingits digestibility (Huntington et
al., 2006). Common processing includes grinding,
pelleting, dry rolling, steam rolling (addition of
water before rolling), and steam aking. All these
processes aim to break grain barriers such as the
pericarp and the protein-starch matrix, allowing
accessof microorganismstostarchgranules.These
processesalsoreducetheparticlesize,andincrease
surfaceareaandmicrobialcolonization(Giubertiet
al., 2014). The response to processing varies with
differentgrains,withsorghum>corn>oats=barley>
wheat(Huntingtonet al.,2006).
Gelatinizationofstarchmakesitmorewater-soluble
anddigestible.AccordingtoHuntington(1997),steam
akingofcornimprovesruminal,post-ruminalandtotal
tractdigestibilitycomparedwithdryrolling(85vs.70%,
92vs.69%,and99vs.90%,respectively).According
toSveinbjörnssonet al.(2007),heattreatmentincreases
starchdegradationduring8hofin vitro incubation,as
follows:0.155vs.0.870forpurepotatostarch,0.491vs.
0.815forpeas,0.686vs.0.913forbarley,and0.351
vs.0.498formaize.
Only a fraction of starch is gelatinazed during
steamconditioningand pelleting offeeds(from10
to200gstarch/Kg).Theexpanderprocessing,onthe
otherhand,addsupto80gwater/Kgwhilethediet
reachesahighpressureandtemperaturesabove100°C,
thusresultinginbetween220and 350 g starch/Kg
gelatinizedduringthisprocess.The extrusion adds
evenmorewater(upto180gwater/Kg)andthediet
issubjectedto evenhighertemperatures(>110°C)
underhighpressure,thusresultinginmorecomplete
gelatinisation and disintegration of starch granules
(Svihus et al.,2005).ThiswasevidencedbyOffner
et al.(2003),whoreported0.607,0.663,0.743,0.746,
0.819, 0.830, and 0.867 effective degradabilities
foruntreated, cracked, ground, pelleted, expanded,
steamakedandextrudedcorn,respectively(passage
rate0.04h-1).Graintypealsoinuencestheresults.
Steamakingofcorneliminatedtheadverseeffects
ofvitreousendospermandprotein-starchmatrix on
digestibilityincomparisonwithdryrolling.Thiswas
contrary to the results obtained for barley, a grain
withahighlydigestibleprotein-starchmatrix,where
nodifferencewasobservedbetweenbothtreatments
(Engstromet al.,1992).
Starch source
The highest effective degradability of starch
in cereal grains was obtained for oats, wheat and
barley,being lower for corn and sorghum. Corn
and especially sorghum have a high proportion
of peripheral and horny endosperm resulting in
increased resistance to microbial activity (Rooney
andPugfelder,1986),unlikewheatandoats,which
have higher proportion of floury endosperm. In
addition, corn and sorghum have a denser protein
matrix(Kotarskiet al.,1992).Thein vitro experiment
byLanzaset al.(2007)measuredfractionalgasrates,
as a measure of starch digestion (Huhtanen and
Sveinbjörnsson,2006),reporting0.26,0.24,0.15,and
0.06h-1 ratesforwheat,barley,corn andsorghum,
respectively(p<0.001).
Cassavahashighereffectivedegradabilitythan
cornandsorghumduetoitslackofpericarp,protein
matrix,hornyandperipheralendosperm;aswellas
lowproportionoflipids,lackofassociationsbetween
starchandprotein,lessamylose,moreamylopectin,
lesshydrogenbonding,andgreaterswelling when
subjected to chemical processes. Cassava starch
is composed exclusively of amylopectin in the
crystalline region and amylose in the amorphous
region, which prevents excessive formation of
hydrogenbondswithamylopectin,allowingamylose
to be readily leached. This is contrary to cereals,
whichhaveamyloseinthecrystallineregion(Zeoula
andCaldasNeto,2001).Effectivedegradabilityof
corn,sorghumandcassava,reported by Offner et
al.(2003),was 0.597,0.603y0.802, respectively
(passagerate0.06h-1).

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Physiological restrictions of the small intestine
Starch digestibility in the small intestine is
limited.Asdigestaowincreases,starchdigestibility
decreases (Huntington et al., 2006). Factors that
limitstarchdigestibilityincludecontrolledglucose
absorption,decientenzymeaccessibilitytostarch
granules,alterationsinruminalandintestinalpH,and
lackofsynchronybetween starch ow throughthe
intestineandamylasesecretion(Owenset al.,1986).
Starchdigestion efciencyinthesmallintestine
variesbetweensources.Tothiet al.(2003)reported
higher digestibility for barley starch in the small
intestine compared with cornstarch, resulting in
higher small intestine absorption in terms of g/Kg
starchingested.
Starch and ruminal acidosis
Starchfermentationincreasesvolatilefattyacids
(VFA) and lactate production, which can reduce
ruminal pH and kill cellulolytic microorganisms,
leadingtodecreasedberdigestibilityanddrymatter
(DM) intake. Additionally, it can cause metabolic
disorders such as acute and sub acute ruminal
acidosis, rumenitis, laminitis, liver abscesses and
polyencephalomalacia(Plaizieret al.,2009).
The risk of ruminal acidosis increases when
starchdigestionrate increases.Thisratevaries with
graintypeandprocessingandgenerallyoccursinthe
followingorder:wheat(32%h)>oat>barley(29%h)
>potato(5%h)>corn(2%h)andsorghum(Callison
et al.,2001;Mosaviet al.,2012).Krauseet al.(2002)
reportedlowerruminalpHinlactatingcowsfedhigh
moisture corn vs. dried corn. Gulmez and Turkmen
(2007) observed a decrease of ruminal pH (<6) in
lactatingcowswhencornwasreplacedbywheat.They
alsoobservedlowpH(<5.8)over13continuoushours
whenwheatwastheonlysourceofstarch.
Cassavaisused asareadily fermentableenergy
source for ruminants. It has a high rate and extent
of ruminal degradation, as evidenced by Khampa
andWanapat(2006)whocomparedcassavavs.corn
supplementation at 1 and 2% of live weight. They
found that 2% cassava supplementation lowered
ruminalpH(5.3vs.6.4)andcellulolyticbacteria(2.3
vs.5.9x107).
Starch and methanogenesis
Ruminal digestion of ber-rich diets increases
hydrogen and carbon dioxide production, which
are substrates for methanogenesis. Moreover,
starch-rich diets change the bacterial ecology by
favoring propionic-acid producing bacteria over
methanogens (Bannink et al., 2006; Ellis et al.,
2008).Propionicacidproductionfromdicarboxylic
acids(aspartate,malate,fumarate)viathesuccinate
pathway is thermodynamically more efficient
than methanogenesis (Offner and Sauvant, 2006).
Moreover,rapidly-fermentingdietsreducemethane
productionbydecreasingruminalpH,whichaffects
thegrowthofmethanogens,protozoa (Hook et al.,
2011)andcellulolyticbacteria(Sunget al.,2007),
andincreasespassagerate,whichreducesprotozoans
and,thereby,interspecieshydrogentransfer(Kumar
et al.,2013).
Agle et al. (2010) reported that diets with higher
proportionofnon-structuralcarbohydrates(52and72%)
resultedinnumerically lowermethaneemissions(1.5
vs.3.4g/hour,respectively),althoughresultsshowed
nodifferenceduetohighvariability.Arecentstudyin
grazingHolsteinFriesiancowsfoundthatconcentrate
level (2, 4, 6, and 8 Kg/cow/day) had no impact on
methane emissions (287, 273, 272, and 277 g/day,
respectively). However, when it was associated with
DMandenergyconsumption,methanedecreasedwith
increasinglevelsofconcentrate(gCH4/KgDM:20,19.3,
17.7,and18.1;CH4-E/grossenergyintake:0.059,0.057,
0.053,and0.054,respectively).Theydemonstratedthat
concentratesupplementationtograzingcowsincreased
milkproductionanddecreasedmethaneemissionsper
unitofmilkproduced(Jiaoet al.,2014).Aguerreet
al.(2011)foundthatchangingforage:supplement
ratio(F/S)from68:32to47:53reducedmethane
emissionsfrom648to538g/cow/day.Pirondiniet
al.(2015)evaluatedtheeffectofstarch(23.7and
27.7%DM)onmethaneemissionsindairycows,
ndingloweremissionsforstarch-richdiets(415
vs. 396 g/d, respectively). Finally,Hatew et al.
(2015) investigated the effect of starch (270 vs.
530g/Kg concentrateDM)andfermentationrate

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(fastvs.slow)indairycows.Theyfoundnodifferences
inmethaneproducedperKgoffat-correctedmilkand
protein,orper KgDMconsumed, orasafraction of
thegrossenergyconsumed.However,thehighstarch
diet(46.9vs.43.1g/Kg)hadlessruminalmethane
per Kg of fermentable organic matter (42.6 vs. 47.4
g/Kg).Haleset al.(2012)evaluatedtheeffectofcorn
processing. They found that Jersey animals eating
steamedcornakesproducedlessmethanethanthose
eatingdryrolledcorn(58.77vs.74.31L/animal,11.65
vs. 14.06 L/KgDMintake,2.47 vs. 3.04% ofgross
energyconsumed,and3.30vs.4.18% of digestible
energ y consu med). The reduction was explained by
differences in ruminal fermentation, changi ng the
placeofdigestion(fromtherumentotheintestine),or
decreasedruminalpH.Scarceliteratureisavailableon
theeffectofstarchsourceandprocessingonmethane
emissions.InastudyreportedbytheCCRP(2012)a
reductionofmethaneemissionsincowsfedground
wheat(219gmethane/day,11.1gmethane/KgofDM
consumed)vs.groundcorn(424and19.5gmethane,
respectively).
The difference in methane production per starch
vs. cellulose unit does not depend on the chemical
composition,asboth carbohydratesarehydrolyzedto
glucosebeforefermentation.Conversely,hemicellulose
polymerincludessugarswith5to6carbons,whichcould
lead to changes in the fermentation prole (different
proportionsofVFA)andmethaneemissions.Ratherthan
thechemicalcomposition,thedifferences in methane
production from starch, cellulose and hemicellulose
appear to be a function of the microbial species that
degrade each substrate. Fermentation patterns and
methaneproductionvaryasmicrobialspeciesadaptto
changes in dietary substrates and ruminal conditions.
Additionally,associative effects between nutrients
inuence methane production, which means that this
gascanbeestimatedforthedietandnotforindividual
ingredients(Knappet al.,2014).
Relationship between starch and milk
composition and yield
Effect on milk yield and fat content
Milk yield response depends on the starch
source(Khorasaniet al.,2001) and its degradation
rate. Mosavi et al. (2012) compared milk yield in
Holstein cows consuming wheat, barley,maize or
potatoes. They found a reduced milk yield for the
diet added with potatoes, and attributed it to its
lower digestibility. Supplementation with rapidly
degradablestarchesinrumen-suchasbarley,wheat
or cassava- increases yield but reduces milk fat
(Sutton, 1989). Poore et al. (1993) found a milk
yieldincreaseof3.4Kg/dayand0.4%fatreduction
whenruminaldigestibilityincreasedfrom48to72%.
Milkfatreductionisassociatedwithchangesinthe
fermentationprole,causedbyarelativereductionin
lipogenicvs.glycogenicprecursors(Reynoldset al.,
1997).Rumenpropionateincreaseswhileacetateand
butyratedecreasewheningestionofrapidlydegradable
starchexceeds7Kg/day(Casperet al.,1990).Jurjanz
et al.(1998)evaluatedstarchsourceand level(wheat
orpotatopeels;<5,6,or>7.5Kg/d)onmilkyieldand
composition.Highstarchconsumptionfrom potato
peels(>7.5Kg/day)leadtoslowerruminaldegradation
andincreasedmilkfatcontent(+3.3g/Kg)compared
towheat.Fedinloweramounts,thestarchsourcedid
notaffectmilkfatsynthesis.Thelowerrateofstarch
degradationcouldhavereleasedmorefatprecursors.
Mosavi et al.(2012)alsoobservedslowerruminal
degradation for corn starch compared with wheat,
barley or potato, as well as increased acetate and
butyrateproductionalongwithhighermilkfat(3.43%
vs.3.12,3.09,and3.13%,respectively).Contraryto
thesendings,Chanjulaet al.(2004)didnotobserve
differences in milk production and compositional
qualitybyaddingcorn(lowdegradability)orcassava
(highdegradability)attwoinclusionlevels(55vs.
75%).
AccordingtoKennellyandGlimm(1998),milkfat
isreducedduetheinhibitoryeffectofmethylmalonyl
CoA(synthesizedfrompropionicacid)onfattyacid
synthesisinthemammarygland.MethylmalonylCoA
accumulation competitively inhibits malonyl CoA
(VanSoest,1994).
Reynoldset al.(1997)associatedmilkfatdecrease
withincreasedlevelsofplasmaglucoseandinsulin
in animals fed high amounts of the supplement.
Insulinlowerslipolysisandpromoteslipogenesisin
adiposetissue,reducingfattyacidsavailabilitytothe
mammarygland,thusdecreasingmilkfat.According
to Van Soest (1994), lipogenesis in adipose tissue

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Gómez LM et al. Starch in ruminant diets: a review
is insulin dependent, which is not the case for the
mammarygland.
Thereductioninmilkfatcanalsobeexplainedby
increasedtrans-unsaturatedfattyacidsintherumen
(Gaynoret al.,1995).Cerealgrainsarehighinlinoleic
and oleic acid. A ruminal pH decrease due to the
dietcandisturbbiohydrogenationofunsaturated18
carbonfatty acidsincreasingtransC18:1fattyacid
(transisomersresultfromincompletemicrobialbio-
hydrogenationoflinoleicacidintostearicacid).Itis
knownthatruminalandmilkincreaseintransC18:1
iscorrelatedwithlowmilkfatlevelsincowsfedhigh
graindiets(Griinariet al.,1998).Corncontainsahigh
concentration of linoleic (C18:2) and octadecanoic
acid (trans C18:1),whichinhibit biohydrogenation
andreducelipogenesisinthemammarygland.
AccordingwithMontoyaet al.(2004),theoptimal
content of nonstructural carbohydrates (NSC) for
maximizingmilkyieldisbetween30and38%ofthe
diet. Those researchers supplemented cows with 4
Kgofacommercialconcentrateand0,6,and12Kg
offreshpotatoes,thusNSCaccountedfor7.2,12.4,
and17.9%ofDMintake.Milkyieldwashigherfor
the potato treatments (17.2 vs. 15.8 liters/cow/day;
p=0.004).Nevertheless,nodifferencewasobserved
fortheinclusionof6vs.12Kgpotatoes,whichcould
beassociatedwithalimitedabilitytousepotatoNSC.
Theirstudyfoundnodifferencebetweentreatmentsfor
fatpercentageand production(p>0.05).Pimentel et
al.(2006)alsoevaluatedcassavasupplementationon
milkyieldandcomposition.Theyreplaced0,25,50,
and75%ofcornwithcassava,ndingalineardecrease
of30and1.15g/dayinmilkyield(correctedfor3.5%
fat)andfatproduction,respectively.Accordingtothe
authors,theviabilityandlevelofcornsubstitutionwith
cassavawilldependonalowcostofsubstitutionthat
compensatesfortheexpecteddecreaseinproduction.
Dann et al. (2014) evaluated three starch levels
(17.7, 21.0, and 24.6%) in Holstein cows using
increasing levels of ground corn. They found that
solids-corrected milk yield was not affected by the
diet, averaging 40.8 Kg/d. They concluded that
starch content did not affect rumen fermentation or
performance.Theirhigheststarchlevel(onaDMbasis)
was between 23 to 30%, which follows within the
recommendedrangeforlactatingcows(Grant,2005).
Delahoyet al.(2003)conductedtwoexperiments
assuming that supplements such as steam-flaked
corn(SFC)andnon-forageber(NFF)sourcesmay
provide benets over corn. In the rst experiment,
animalswereassignedtoacracked-corn(CC)orto
asteam-akedcorn(SFC)supplement.Inthesecond
experiment,animalswereofferedgroundcorn(GC)
ornoforagesourcesofber(NFF).No differences
wereobservedinmilkyield(24.3and27.5Kg/dfor
experiments1and2,respectively),explainedbyalack
ofdifferenceinnetenergyconsumptionforlactation,
which exceeded the requirements (Experiment 1).
Anotherfactorthatcouldexplaintheseresultsisthe
qualityofthepasture,whichdidnotreducethepH,a
targettoimprovebyNFFinclusioninExperiment2.
Effect on the protein content
Dietsrichinnonstructuralcarbohydratesincrease
ruminalammonianitrogenutilizationandmicrobial
protein synthesis (Svihus et al., 2005). Therefore,
whendietaryenergyincreases,metabolizableprotein
is also increased. Mosavi et al. (2012) evaluated
theeffectof four starch sourcesonmilkproteinin
Holstein cows. While protein levels of milk were
similar (3.03, 3.10, 3.14, and 3.04%) for wheat,
barley,corn and potato supplements, respectively,
milkproteindifferedin favor of wheat, barley and
corn,comparedtopotato(1.08,1.06,1.06,and0.98
Kg/d,respectively; p=0.02).GozhoandMutsvangwa
(2008)foundnodifferenceinmilkproteinforanimals
feddietsbasedonwheat,barleyorcorn,buthigher
milk protein was observed for diets based on corn
vs. oats. On the contrary, other studies comparing
slowversusfastruminaldegradingstarchesfoundno
differencesin milkprotein(Khorasaniet al., 2001;
Silveira et al.,2007;Cabritaet al.,2009).
It has been suggested by Huhtanen and
Sveinbjörnsson(2006)thatenhancedstarchdigestion
in the small intestine increases milk protein,
perhapsbysparingaminoacidsfrombeingusedfor
gluconeogenesisintheliver.Theyreportastudyin
whichmilkproteinyieldwasslightlybutsignicantly
higherformaizecomparedwithbarleysupplements.
Contrarytothisconcept,increasingstarchdigestion
intherumenisconsideredadvantageousintermsof
milkproteinyield,sinceitincreasestheenergysupply
formicrobialproteinsynthesisandthemetabolisable

87
Rev Colomb Cienc Pecu 2016; 29:77-90
Gómez LM et al. Starch in ruminant diets: a review
protein ow to the small intestine (Thair, 2012).
Finally, Reynolds (2006) reports a study in which
therewasnoevidencethatthesiteofstarchdigestion
increasedmilkproductionorchangeditscomposition.
Final thoughts
Rumenfermentationofstarch-althoughitreduces
energy efciency over the enzymatic digestion in
the intestine- determines its nutritional value for
ruminants. The rate and extent of ruminal starch
digestion alters pH, cellulolytic activity, microbial
proteinsynthesis,methaneemissionsand,eventually,
animalproduction.Thereisa considerablebodyof
researchon degradation potential of various cereal
grains, but little information on non-traditional
sourcesofstarchthatcouldreplacecerealgrainswhen
availabilityandcostsarecompetitive.Thestructural
traitsofstarch fromthesesources,their interaction
withothercomponents,andtheeffectofprocessing
should be examined. In vitro digestion techniques
constituteastartingpointforstudyingtheextentand
kineticsofstarchdegradationfromnon-conventional
sources.
Starch is the main energy component used in
ruminants feed to modulate ruminal fermentation
andpromote sync with the nitrogen sources. More
researchisrequiredtoevaluatetheeffectofusingone
ormoresources of starch —with different degrees
of degradability and processing— on protein use
efficiency, milk yield and compositional quality.
Studiesshouldfocusonadditionlevelsandnutrient
composition of the forage base according with the
stage of lactation and energy requirements of the
animal.
Acknowledgements
The Administrative Department of Science,
TechnologyandInnovation(Colciencias,Colombia,
call 569 of 2012. Code 1115+569-33874) and
the Sustainability Strategy 2014-2015 (CODI,
UniversidaddeAntioquia,Colombia)supportedthe
research project entitled “Evaluación in vitro e in
vivodediversasestrategiasnutricionalesparamitigar
las emisiones de metano y su impacto productivo,
reproductivo y económico en ganadería de leche
especializadaenelnortedeAntioquia”,whichmade
possiblethisliteraturereview.
Conict of interest
Theauthorsdeclaretheyhavenoconictsofinterest
withregardtotheworkpresentedinthisreport.
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