動物科學外文翻譯

Dustbathingbybroilerchickens:acomparison

ofpreferenceforfourdifferentsubstratesSaraJ.Shields,JosephP.Garner,JoyA.MenchDepartmentofAnimalScience,UniversityofCaliforniaatDavis,oneShieldsAvenue,Davis,CA95616,USAReceived28February2003;receivedinrevisedform28August2003;accepted21January2004AbstractLegabnormalitiesleadingtolamenessinbroilerchickensareaseriouswelfareproblem.Previousworkinourlaboratorydemonstratedthatprovidingbroilerchickenswiththeopportunitytoexercisebyperformingmorenaturalbehaviors(suchasperching,walkingupanddowninclinesanddustbathing)canimprovetheirabilitytowalknormally[J.A.Mench,J.P.Garner,C.Falcone,Behavioralactivityanditseffectsonlegproblemsinbroilerchickens,in:H.Oester,C.Wyss(Eds.),ProceedingsoftheSixthEuropeanSymposiumonPoultryWelfare,World'sPoultryScienceAssociation,Zollikofen,Switzerland,2001,pp.152—156].Withthelong-termgoalofstimulatingdustbathingtoimprovelegcondition,theaimofthisstudywastodeterminethedustbathingsubstratepreferredbybroilerchickens.Weconductedadustbathingchoicetestexperimentusingfourdifferentbeddingtypes(pinewoodshavings,ricehulls,constructiongradesand,andarecycledpaperanimalbeddingproduct).Fourdifferentbroilerchickensweretestedeachweekfor6weeksstartingwhenthechickswere1weekold.Theywereselectedfromtwogroupsofbroilerchickenshousedinlargehomepensbeddedwithwoodshavings.Selectedbirdsweretestedinsmallerpenswheretheyweredeprivedofallloosebeddingmaterialexceptduringtesting,whichwascarriedoutfor1heachdayforthreeconsecutivedaysperweek.Duringanobservation,eachcornerofthetestpenwasfilledwithadifferentbeddingtype,andthebehaviorofthefocalchickrecorded.Verticalwingshakes(VWS)wereusedastheprimarymeasureofdustbathingactivity.BroilersperformedsignificantlymoreVWSperhourinsand(F3,36=13.52,P<0.0005)andspentagreaterproportionoftheirtotaltimeinsand(F5,60=5.15,P=0.001)thaninthericehulls,paper,orwoodshavings.Theyalsovisitedthesandsignificantlymoreoftenthanthepaperorthewoodshavings(F5,60=96.47,P<0.0005).Therewerenodustbathsinthericehulls.Thelatencytoentersandwassignificantlyshorterthanthelatencytoenteranyoftheotherthreesubstrates(F3,15=5.24,P=0.0113).Groundpeckinggenerallyprecedesadustbathingbout,andtherateofpeckingandtheproportionofthetotaltimebudgetspentpeckingwerealsohighestforsand(F3,51=24.49,P<0.0001andF3,51=15.28,P<0.0001,respectively).Thepreferenceforsandwasapparentinthefirstweek,andwasstablewithage.Theresultsofthisstudysuggestthatsandisattractivetobroilerchickensandisapotentstimulusfordustbathing.Furtherworkisneededtodetermineifstimulatingbroilerchickenstodustbathebyprovidingsandcanimprovetheirlegcondition,andthustheirwelfare.?2004ElsevierB.V.Allrightsreserved.1.IntroductionExerciseisessentialforthehealthandwell-beingofanimals.Forbroilerchickensevenwalkingmaybedifficultasthebirdsageduetorapidgrowthrateandtheincreasingincidenceoflegdisorders(Weeksetal.,2000;Kestinetal.,1992;Mench,2004).Previousworkinourlaboratory(Menchetal.,2001)andotherwork(ThorpandDuff,1988)suggestthatexerciseisimportantforreducingtheincidenceandseverityoflegproblems.Forbroilerchickens,oneformofexerciseisdustbathingbehavior.Becausedustbathinginvolvesrotationalandpushingmotionsofthelegs,itcouldbeaformofexercisethatimproveslegcondition.Layinghenshavebeenfoundtohaveclearpreferencesfordustbathingsubstrates(PetherickandDuncan,1989;VestergaardandBaranyiova,1996;vanLiere,1991),butthepreferencesofbroilerchickenshavenotyetbeenthoroughlyexamined,particularlyforbeddingthatisavailableonacommercialscaleintheUS.Ouraimwastodeterminewhichsubstrate,outoffourcommerciallyavailablebeddingtypes,wasthebestforelicitingdustbathingbybroilerchickens.Adustbathingboutiscomposedofasequenceofbehavioralcomponents(Kruijt,1964).Peckingandscratchingatapotentialdustbathingsiteusuallyprecedeadustbathingbout.Thesequenceofdustbathingbehavioralcomponentsusuallybeginswith“bill-raking”,wherethebird,inasittingposition,pullsloosesubstrateclosertoitsbody,constructingasmallridgeofloosesubstrate.Then,whilestillinasittingposition,thebirdperformsverticalwingshakes(VWS)duringwhichsmallparticlesaretossedupwardintothefeathers.Oncedirtparticleshavebeencollectedinthefeathers,thebirdliesdownonitssideandperforms?side-rubs‘or?head-rubs'.Side-rubsinvolvemotionofthelegsasthebirdpushesitsbodywhileinalyingposition.Whenthedustbathingbirdisfinishedwithitsbath,itstandsandconcludestheboutwitha'ruffle-shake',shakingoffloosedirtparticles.Theworkingofloosesubstratelikedustordirtthroughthefeathersisthoughttofunctioninabsorbingstalelipidsintheplumage(vanLiere,1991).Undercommercialrearingconditions,broilerchickensmaynothaveaccesstoloosefriablesubstrateduringthewholegrowingperiodbecausetheirbeddingbecomescompressedanddirtywithuseovertime.Inthissituation,dustbathingmaynotbeelicitedtoitsfullest.Likelayinghens,broilerchickensprobablyalsohavepreferencesforparticularsubstratesinwhichtodustbathe.Ifthebeddingprovidedisnotofapreferredtype,itmayfurtherdeterthemfromdustbathing.Youngandadultlayingstrainchickenspreferpeattosand,andsandtowood-shavingsandstraw,fordustbathing(PetherickandDuncan,1989;Sanotraetal.,1995;vanLiere,1991;VestergaardandBaranyiova,1996).However,dustbathingpreferencesofbroilerchickenshavebeenexaminedinonlyonestudy.VestergaardandSanotra(1999)providedbroilerchickswitheithersandorstrawinwhichtodustbathefortwenty-six1hsessions.Severalofthebirdsdidnotdustbatheoneverydaythesubstrateswerepresented,andthenumberofdaysinwhichdustbathingdidnotoccurwasalmosttwiceasmanyforthosebirdsgivenstrawthanthosegivensand.Thisresultsuggeststhat,atleastforsandandstraw,broilerandlayerpreferencesaresimilar.However,thedustbathingchoicetestsperformedsofarusingbroilerchickenshavenotevaluatedanyoftheothersubstratestestedforlayinghens,orthecommerciallyavailablebeddingtypesthatwouldbeeasytoobtaininlargequantitiesintheUS.Beforetheeffectofdustbathingaloneonlegconditioncanbeassessed,theconditionsthatwillelicitthemostdustbathingbehaviorfromabroilerchickenneedtobedetermined.Thepresentexperimentwasperformedinordertodeterminewhichoffourbeddingtypes,woodshavings,ricehulls,masonrygradesand,andarecycledpaper-beddingproduct,wouldelicitthemostdustbathingbehaviorincommercialstrainbroilerchickens.ThesesubstrateswerechoseneitherbecausetheyarealreadyinwidespreaduseintheUS,areavailableonacommercialscale,orarebeingconsideredasalternativestotraditionalbedding(Grimesetal.,2002).Weexamineddifferencesintheamountofdustbathingperformed,thelatencytoperformdustbathing,thelatencytoentereachsubstrate,theamountoftimespentineachsubstrate,thenumberofvisitstoeachsubstrate,thelengthofadustbathingboutineachsubstrate,andtheamountofpre-dustbathingappetitivepeckingbehaviorperformedineachsubstrate.2.MethodsSubjectsandhousingThisstudy,whichwaspartofalargerstudyoftheeffectsofstraindifferencesongait,wasapprovedbytheUniversityofCalifornia,DavisAnimalUseandCareAdministrativeAdvisoryCommittee.Cobb(N=52)andRoss(N=52)day-oldmalebroilerchickswereobtainedfromacommercialhatchery.Thebirdsweremarkedwithcolored,numberedidentificationtags.Halfofthebirdsofeachstrainwereplacedinonefloorpen(measuring3.05msquare),andtheotherhalfofthebirdswereplacedinanidenticaladjacentfloorpen.Eachpencontainedwoodshavingsforbeddingandanoverheadbrooderforheat.Therewerewindowsalongthelengthofthebuildingthatalloweddaylighttoenterthepens.Overheadfluorescentlightswereoncontinuouslyforthefirst4weeks,andwerethenadjustedtoprovidean8D:16Lschedule.Food(PurinaMillsMeatBuilder,containing20%crudeproteinandwithoutaddedmedication)andwaterwereavailableadlibitum.Mortalitywaslow(onlyonechickfrompen1died,atthestartofthesecondweek).SubstratepreferencetestsEachweek,beginningwhenthechickswereonewkoldandendingwhentheywere7weeksold,eightRosschicks(fourfocalbirdsandfourpair-mates)wereremovedfromthetwohomepensandtakentoadifferentroominthesamebuildingtotestsubstratepreference.Nochickwaseverusedtwice.Thechickswereplacedinpairsintooneoffourdifferent1.52mXl.52mexperimentalpens(Fig.1),constructedofwoodandchickenwire,fordustbathingsubstratechoicetests.Chicksremainedinthesepensfor4days.Theexperimentalpenshadaraisedfloorsothatthecornersofthepenfloorcouldberemovedtoaccesssquare(0.61mX0.61m)10cmdeepboxessunkenintothecorners.Theboxeswereeachfilledtothetopwithadifferentsubstrate,suchthatthesurfacewasevenwiththefloor.Chicksthereforedidnothavetostepupordowntogetintooroutofthebox,sincethiscouldhavepreventedthemfromenteringthebox,ormadeitmoredifficultforthemtoexitonceinsidethebox,especiallyastheygrewanddevelopedlegproblems.Foodandwaterwerelocatedinthecenterofeachpen.Whenthechickswerenotbeingtested,thecornerscontainingthedifferentdustbathingsubstrateswereclosedwithawoodenlidandtheentirepenfloorwascoveredwithlabbenchpaper.Thismaterialkeptthechickscleananddrywhilestillallowingustodeprivethemofloosebeddingmaterialuntilthebeginningofeachtestsession.Twoheatlampswerehungabovethecenterofeachpen;thesewereraisedasthechicksgrewsothatthepenwaskeptatatemperatureappropriatefortheirage(FASS,1999).Thelightcycleinthetestingroomwasthesameasthatinthehomepenarea,butthetestingroomdidnothavewindows.Onechickineachpenwasdesignatedasthefocalchickandmarkedonthebackwithanon-toxicmarker.Chicksweretestedinpairstoreducefearfulness,butdatawerecollectedonlyonthefocalbird.Thechicksweregivenapproximately24htohabituatetothetestingenvironmentwithoutaccesstoloosebeddingbeforeobservationsbegan.Beforeeachtest,thefourdifferentsubstrates(ricehulls,constructionsand,woodshavings,andarecycledpaperwasteproduct)wererandomlyallocatedtoeachcornerofthetestingpen,butthesesubstratesremainedcovereduntiltheobservationsbegan.Immediatelyprecedingeachobservation,chickswerecorralledintothecenteroftheexperimentalpenusingacardboardbox,andthesubstrateswereexposed.Thecardboardboxwasthenliftedtoallowthechickstomovefreelyaroundthepen.Eachobservationlastedfor1h.Therewerefourobservationsperdayandthreeconsecutivedaysoftestingperweek.Thefirstobservationeachdaybeganapproximately4hafterthelightscameonandwasthenfollowedbythenextthreeobservationsforthatdaysothateachpenwasobservedasclosetopeakdustbathinghours(Vestergaardetal.,1990;HoganandVanBoxel,1993;StatkiewiczandSchein,1980)aspossible.Wecontinuouslyrecordedbehavioraldatafromthefocalchickusingalaptopcomputerwithacustom-designedMicrosoftAccessprogram.Wedividedthepenintosixdifferentareastorecordthelocationofthefocalchick:thepencenter,thewalkways,andthefourdifferentdustbathingareas.Thelatencytoenterandtheamountoftimespentineachareaofthepenwererecorded.Thenumberofpecks,scratches,verticalwingshakes(VWS),headrubs,siderubsandruffleshakes,andthetime(numberofsecondsfromthebeginningoftheobservation)thateachoftheseeventsoccurredwererecordedbyanobserverwhosatapproximately0.5maway.Eachfocalchickwastestedthreetimes,oneachofthreeconsecutivedays.DustbathingoccursindiscreteboutsorganizedaroundtheperformanceofVWS.Thus,adustbathingboutwasdefinedasbeginningatthetimeafocalbirdperformedhisfirstVWSinadustbath,andendingwhenaVWSwasfollowedby5minormorewithoutanyfurtherVWS.Thus,twoormoreVWSwithlessthan5minbetweenthemwereconsideredpartofthesamedustbathingbout.StatisticalanalysisAllanalyseswereperformedusingGLM(Minitab12forWindows;SASv8forWindows).ThenumberofVWSperhourineachsubstratetype,thepercentofthetotalobservationtimeeachfocalbirdspentineacharea(empty,center,orsubstrate),andthepercentoftotalvisitsabirdmadetoeachareawereanalyzedusingrepeatedmeasuresGLM,withrepeatedmeasuresmadeonbirdnestedwithinhomepenandageattesting.Substrateandageattestingwerethevariablesofinterestinalltheanalysesexceptone(latencytoentereachsubstrate).VWSperhourdataweresquare-roottransformed,andtheproportionofthetotalobservationtimeandproportionofthetotalvisitswereangulartransformed,tomeettheassumptionsofGLM;thesuccessofthetransformationswasconfirmedposthoc.Significanteffectswereinvestigatedpost-hocusingTukey-correctedpairwisecomparisons.Thefamilyerrorrateforthesecomparisonswassetat0.05.Wealsoexaminedseveralmeasuresofpreferenceusingdatacollectedonboutlengthandvariouslatencies.Theseincludedlatencytothefirstverticalwingshakeabirdperformed,latencytoenterthefirstsubstrateinthesession,latencytoentereachdifferentsubstratewithinthesession,andthelatencytoenterthefirstsubstrateinwhichadustbathoccurred.Analysesofthelatencydata,anddatacomparingboutlengthsineachofthefoursubstrates,werecomplicatedbythefactthatnoteverybirdenteredordustbathedineverysubstrate,andsometimesbirdsenteredanddustbathedinsubstratesduringmorethanonetestingsession.Toavoidpseudoreplication,onlyonedustbathwasusedforeachbirdinanyoneanalysis.Dustbathswereselectedinapseudo-randommanner,sothatthenumberofdustbathsforeachsubstratewasmaximized.Thiscreatedamorebalanceddatasetinwhichtherewereasmanydustbathsineachsubstratetypeaspossible.Alllatencyandboutlengthmeasureswerelogtransformedbeforeanalysis.Forcasesinwhichthesamebirddustbathedinthesamesubstrateduringmorethanonetestingsession,weaveragedthelatenciesandtheboutlengthsacrossthesessionsaftertransformingthem.Formostoftheseanalyses(exceptlatencytoentereachsubstrate),homepenwasusedasablockingfactorandageattestingandsubstratewerethevariablesofinterest.Alargerdatasetwasavailableforthelatencytoentereachsubstratemeasurebecausemostbirdsenteredmostofthesubstratesoverthecourseoftheirthreetestingsessions.Inordertoachieveabalanceddataset,werandomlychoseonebirdfromeachhomepenateachage(i.e.12birdsintotal).Becauseeachbirdwasonlytestedatoneage,thetermhomepenXageuniquelyidentifiedeachbird.WethereforeperformedarepeatedmeasuresGLMbytreatingthetermpenXageasarandomfactorinamixedmodel.Thesubstratetermwasthentheonlyfactorofinterest.Forthelatencytoenterthefirstsubstrateinasession,wewereunabletocreateadatasetthatwasbalancedbyageattestingbydiscardingdataasintheanalysisoflatencytoentereachsubstrate.Onesubstratewasrandomlychosenforeachbirdsothateachsubstratewasrepresentedbysixdatapoints(i.e.sixbirds),thuscreatingadatasetthatwasbalancedbythesubstratetermbutnotbyageattestingterm.Theageattestingtermwaslogtransformedtoimprovethelinearityanderrorstructureofthedata,andwasthentreatedasacovariate.Inordertodeterminewhetherbirdswerechoosingthefirstsubstrateenteredinordertodustbathe,weassessedwhetherthesubstratefirstenteredpredictedwhetherbirdsstayedtodustbatheinthatsubstrate.Foreachsubstratewecountedthenumberofoccasionsonwhichabirdenteredthatsubstratefirstinthesessionandstayedtodustbatheversusthenumberofoccasionsonwhichabirdenteredthatsubstratefirstinthesessionandthenmovedontofirstdustbatheinadifferentsubstrate.Thesedatawereanalyzedusinga4X2chi-square.Thefinalanalysiswasperformedongroundpecking,andthepotentialdifferenceintheperformanceofthisbehaviorwhilebirdswereineachofthedifferentsubstrates.Themeanrateofgroundpeckingduringtheobservationperiod(i.e.pecksperhour)wascalculated.Theproportionoftimeduringtheobservationperiodspentpeckingwasalsocalculated.ThesewereanalyzedusingrepeatedmeasuresGLM,withbirdnestedwithinhomepenandageattesting.3.ResultsWeobservedatotalof27dustbathingbouts.Ofthese,20wereperformedinsand,6inpaper,and1inwoodshavings.Nofocalbirdeverdustbathedinthericehulls.Afteraveragingthedataforbirdsthatdustbathedinthesamesubstratefortwoorthreesessions,therewere21dustbaths.ThemeannumberofVWSperdustbathwas21.06±2.44.WealsoobservedtheperformanceofasingleVWSonthreeseparateoccasions,onceinthesand,onceinthewoodshavings,andonceinthericehulls.TherateofVWSperhourwassignificantlyaffectedbythesubstrateinwhichabirddustbathed(repeatedmeasuresGLM:F3,36=13.52,P<0005;Fig.2).PosthoctestsrevealedthattherateofVWSperhourwashigherinsandthaninanyothersubstrate.TherewerenodifferencesinVWSperhouramongtheremainingthreesubstrates.Therewasalsoasignificantdifferenceintheproportionofthetotalvisitsmadetothedifferentlocationsinthepen(repeatedmeasuresGLM:F5,60=96.47,P<0.0005;Fig.3A).Posthoctestsshowedthattheproportionofvisitswashighestfortheemptyareasofthepenthatbirdshadtocrossinordertoenteranothersubstrate.Thecenterofthepenwherethefoodwaslocatedwasvisitedsignificantlylessthantheemptyareasofthepen,butsignificantlymorethananyofthedustbathingsubstrates.Thesandwasvisitedsignificantlymoreoftenthanthepaperorthewoodshavings.Therewasalsoasignificantdifferenceintheproportionofthetotaltimespentindifferentresources(repeatedmeasuresGLM:F5,60=5.15,P=0.001;Fig.3B).Posthoctestsrevealedthatthebirdsspentmoretimeinthesandthaninthericehulls,paper,orwoodshavings.Averagelatenciestoenterthefirstsubstrate,performthefirstverticalwingshake,andenterthefirstsubstrateinwhichafulldustbathoccurredduringasession,were3.32±1.29,18±2.62,15.22±2.72min,respectively.Therewerenosignificantsubstratedifferencesforthesemeasures.Therewas,however,asignificantdifferencebetweenthelatenciestoentereachofthefoursubstratesinatestingsession(repeatedmeasuresGLM:F3,15=5.24,P=0.0113;Fig.4).Tukeypairwisecomparisonsrevealedthatthelatencytoenterthesandwassignificantlylessthanthelatenciestoenterthericehulls,paper,orwoodshavings.Therewerenodifferencesindustbathingboutlengthsinthedifferentsubstrates(GLM:F2,15=2.37,P=0.164).Theaveragedustbathingboutlengthwas14.78±1.9min.Chi-squarerevealedthatbirdsweredisproportionatelymorelikelytoenterthesandfirstandstaytodustbathethantheyweretoenteranothersubstratefirstandstaytodustbathe(chi-square=16.62,d.f.=3,P=0.0017).In14outof27sessionsinwhichweobservedVWS,thefirstVWSobservedoccurredintheresourcethebirdfirstentered.In11outof14ofthesecasesthebirdfirstenteredanddustbathedinthesand.Thus,thebirdsstayedtodustbathein11/12caseswherethesandwasfirstentered;2/7caseswherethepaperwasfirstentered;0/7caseswherethericehullswerefirstentered;and1/2caseswherethewoodshavingswerefirstentered.Forrateofpecking,therewasasignificantdifferencebetweenthenumberofpecksperhourineachsubstrate(repeatedmeasuresGLM:F3,51=24.49,P<0.0001).TheLSM±S.E.M.forpecksperhourinsandwas534±2.6.Forpaper,ricehullsandwoodshavingstherateswere46±2.6,54±2.6,and76±2.6,respectively.Therewasalsoasignificantdifferenceintheproportionofthetotalobservationtimespentpecking(repeatedmeasuresGLM:F3,51=15.28,P<0.0001;Fig.5).Tukeypairwisecomparisonsshowedthatthereweresignificantlymorepecksinsandthaninanyoftheothersubstratesandthattherewassignificantlymoretimespentpeckinginthesandthaninanyoftheothersubstrates.Therewerenogeneralage-relatedtrendsinpreferenceoramountofdustbathingfor:rateofVWS(repeatedmeasuresGLM:F5,12=0.78,P=0.0.585);timespentineachsubstrate(repeatedmeasuresGLM:F5,12=0.74,P=0.607);proportionoftotalvisits(repeatedmeasuresGLM:F5,12=0.75,P=0.602);latencytodustbathe(GLM:F5,15=0.19,P=0.958);orboutlength(GLM:F5,15=3.59,P=0.063).Therewerealsonochangesinpeckingpreferencewithage(F15,51=0.72,P=0.7537),orinpeckingingeneralwithage(F3,51=0.91,P=0.4816).4.DiscussionSandwaspreferredfordustbathingovertheotherthreebeddingtypestested.BroilerchickensperformedsignificantlymoreVWSperhourinsand,andspentsignificantlymoretimeinsandthaninthericehulls,paper,orwoodshavings.Theyenteredthesandinsignificantlylesstimethantheotherthreesubstratesandvisitedthesandsignificantlymoreoftenthanthepaperorthewoodshavings.Pre-dustbathingbehavior(pecking)wasalsosignificantlyhigherinthesandthanintheotherthreesubstrates.Althoughthelatencytoenterthesandwassignificantlylowerthanthelatencytoenteranyoftheotherthreesubstrates,therewasnodifferenceinthelatencytodustbatheonceinasubstrate.Further,therewasnodifferenceinthelatencytoenterthefirstsubstrateinwhichadustbathoccurred.Thissuggeststhatalthoughthesandwasmoreattractiveoverall,thebroilersdidnotinitiallyenteritinordertodustbathe.Thesandappearstohavebeeninitiallymoreinterestingforexploringorforagingratherthanfordustbathing,andinfactthechickensseemedtobeattractedtothesandbecausetheywantedtoingestit.Insomeobservations,peckingatthesandlastedforaslongas20min,anditappearedthatthechickensswallowedmanyoftheparticles.Boththerateofpeckingandtheproportionofthetotaltimeduringtestperiodsspentpeckingweresignificantlygreaterinthesandthaninanyoftheothersubstrates.Thisbehaviorsuggeststhatthemotivationtofindandingestsmallpebblessuchasthosefoundinsandtoaidindigestionmaystillbepresenteventhoughbroilersdonotneedgritinordertodigestcommerciallypreparedrations.Highmotivationtoingestgritwouldhaveimportantwelfareimplications,andthistopicshouldbeexaminedinfuturestudies.Althoughithasbeenproposedthatearlypeckingexperienceinasubstratemightinfluencelaterdustbathingactivityinthatsamesubstrate,aclearpredictiverelationshiphasnotbeenshown(VestergaardandBaranyiova,1996;Nicoletal.,2001).VestergaardandBaranyiova(1996)foundthatchickspeckedsignificantlymoreinthesubstratetheypreferredfordustbathing,andthisresultagreeswithourfindings.Whatmakesthesamesubstratedesirableforbothpeckinganddustbathingisunknown.Presumably,earlypeckingexperiencewouldfacilitatelearningaboutthepropertiesofasubstrateandallowtheexperiencedchicktomakedecisionsaboutdustbathingbasedontheinformationpreviouslygatheredaboutthesubstratessuitability.Butinourstudy,earlypreviousexperiencewasnotnecessaryorderforonesubstrate(sand)toelicitsignificantamountsofbothpeckinganddustbathing.Texture,taste,color,andcontrastofdifferentsubstrateshaveallbeensuggestedasimportantfactorsinfluencingpreference.Thevariableparticlesize,shapeandcontrastingcolorofconstructionsandprobablymakeitvisuallymoreinterestingthantheothersubstratesandonceabirdbegantoinvestigatebypecking,hemayhavesimplystayedtodustbatheaswell.Thefindingthatsandispreferredovertheothersubstratestestedisnotsurprisinggiventheresultsofotherdustbathingsubstratechoicestudies,whichgenerallyshowthathensprefermaterialscomposedoffineparticlesfordustbathing.However,ourresultsareonlypartiallycomparabletothesepreviousstudies,becausewetestedtwosubstrateswhichhavenotbeentestedbefore(ricehullsandrecycledpaperbedding)andwedidnottestonehighlyattractivesubstrate,peatmoss(PetherickandDuncan,1989;VestergaardandBaranyiova,1996),becauseitisnotwidelyavailableintheUSforuseasbedding.Inastudythatagreeswithourresults,vanLiere(1991)foundthatsandwaspreferredtowoodshavings.Theysuggestthatthispreferencemaybeduetothesuperiorityofsandatpenetratingthefeathersandreachingthedownyportionoftheplumage.Twootherdustbathingchoiceexperimentsinwhichsandorwoodshavingsweretestedshowed,first,thatmaleLeghornchicksprefersandtostraw,whilestrawandwoodshavingsareequallyattractive(Sanotraetal.,1995),andsecond,thatbroilerchickensperformmoreverticalwingshakesinsandthaninstraw(VestergaardandSanotra,1999).Itwasdifficulttopredicttheeffectofwoodshavingsinthehomepenontheoutcomeofourpreferencetestintheexperimentalpens.Previousexperiencewithwoodshavingscouldhavemadethebroilersmorelikelytodustbatheinthissubstratebecauseitwasfamiliar.Thistypeofeffect,wheredustbathinginalesspreferredsubstrateinitiallyreducestheeffectivenessofahighlypreferredsubstrateinelicitingdustbathing,wasshownbyVestergaardandLisborg(1993).Bythelastweekofourstudy,thechickenshad5weeksofexperiencewithwoodshavingsintheirhomepensbeforebeingtestedintheexperimentalpens,givingthemampleopportunitytodevelopastrongassociationbetweenwoodshavingsanddustbathing.However,ourresultsweremoreconsistentwiththoseofvanLiere(1991),whofoundthathenswithpreviousexperiencewithwoodshavingsandhensraisedinwire-flooredcagesa