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1 University of Nebraska - Lincoln Digital
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USDA, ARS, Roman L. Hruska U.S. Meat Animal Research Center U.S. Meat Animal Research Center Roman L. Hruska U.S. Meat Animal Research Center CORE Metadata, citation and similar papers at core.ac.uk Provided by UNL | Libraries GrowthandpubertaldevelopmentinBrahman-,Boran-,Tuli-,BelgianBlue-,Hereford-andAngus-siredF1bullsD.D.LunstraandL.V.CundiffUSDA,ARS,RomanL.HruskaU.S.MeatAnimalResearchCenter,ClayCenter,Nebraska68933 Growthandtesticulardevelopmentbe-tween7and15moofagewereevaluatedinbullspro-ducedbymatingsiresofsixbreeds(Hereford,Angus, 2003AmericanSocietyofAnimalScience.Allrightsreserved.J.Anim.Sci.2003.81:1414–1426Breeddifferencesinperformancecharacteristicsare Mentionoftradenamesisnecessarytoreportfactuallyonavail-abledata;however,theUSDAneitherguaranteesnorwarrantsthestandardoftheproduct,andtheuseofthesamebyUSDAimpliesnoapprovaloftheproducttotheexclusionofothersthatmayalsobesuitable.TheauthorsthankA.Krugerforhisskillfultechnicalassistance, BreeddifferencesforpubertyinbeefbullsTable1.NumbersofFbulls(n234)evaluatedforpubertaldevelopmentduring3-yrGermplasmEvaluationProject(CycleV;born1992to1994) Dambreed SirebreedHerefordAngusMARC-IIITotalFbulls(n) Hereford0181432Angus801624Brahman9162247Boran9151943Tuli11151844BelgianBlue10142044AllFbulls4778109234 BullswerebornbetweenMarchandMayofeachspring,numberofbullsevaluatedfromeachsirebreedanddambreedwasbalancedeachyear,andtotalbullswasverysimilareachyear(79,78,and77bullsbornin1992,1993,and1994,respectively).hashighfertility,andishighlyadaptedtostressfultropicalconditions(Frischetal.,1997;Gaughanetal.,1999).TheTuliisabreedbelievedtohavebeendevelopedfromBostauruscattlethousandsofyearsagoinAfrica,andithasdemonstratedhighfertilityandmaternalperformance(Frischetal.,1997;Gaughanetal.,1999).BelgianBlueisacontinentalEuropeanbreedexhibitingapropensityforincreasedmuscling(Arthur,1995;Casasetal.,2001;Wheeleretal.,2001).ThisreportpresentsresultsfromCycleVoftheGermplasmEvaluationProjectatClayCentercharacterizingF1bullsofthesebreedscomparedtoHereford-andAngus-siredcrossesfortesticulardevelopmentandpuberty.MaterialsandMethodsThisstudywasconductedattheU.S.MeatAnimalResearchCenter(40Nlatitude,98Wlongi-tude)locatednearClayCenter,Nebraska.SixbreedsofsireswereevaluatedbytopcrossingonAngus(n~500),Hereford(n~350),andMARCIII(1/4Angus,1/4Hereford,1/4Pinzgauer,1/4RedPoll)composite(n~550)cowseachyear,asdescribedbyCundiffetal.(1998).Allcowswere4yrofageorolder.AngussireswerebredtoHerefordandMARCIIIcows,andHere-fordsireswerebredtoAngusandMARCIIIcows.AllothersirebreedswerematedtoAngus,Hereford,andMARCIIIcows.Matingsweremadeovera3-yrperiod,andasampleofabout80males(8to11malessiredbyHerefordorAngus;14to16byBrahman,Tuli,Boran,orBelgianBluesires)wereleftintacteachyear(1992to1994)toevaluategrowthandpubertaldevelopmentinF1bulls(Table1).BullswerebornbetweenMarchandMayofeachspring.Toobtainarepresentativesampleofabout80maleseachyear,approximatelyev-erythirdbullcalfbornwithinsirebreedwasleftintacteachyear.Forsirebreedswithrelativelylargenumbersofsires(Hereford,Angus,Brahman,andBelgianBlue),eachsirewasrepresentedbyonetotwomaleoffspringperyear,whileeachTuliandBoransirewasrepre-sentedbytwotovemaleoffspringeachyear.Numberofbullsevaluatedfromeachsirebreedanddambreedwasbalancedeachyear,andtotalbullsevaluatedwasverysimilareachyear(79,78,and77bullsbornin1992,1993,and1994,respectively).RangeofF1bullagewas42to47dwith

2 ineachyear,andagerangewithinsirebreedwas
ineachyear,andagerangewithinsirebreedwas32to37dineachofthe3yr.Atotalof234F1bullswereevaluatedinthisstudy.SireBreedsSemenfrom14polled-andfourhorned-HerefordsireswasusedwithAngusandMARCIIIcowstoproduceF1intactmaleprogeny.EightoftheHerefordsireswerebornfrom1982to1984andwereusedinpreviousevaluations(Cundiffetal.,1990),and10sireswerebornafter1985.Semenfrom18AngussireswasusedwithHerefordandMARCIIIcowstoproduceF1intactmaleprogeny.FourAngussireswerebornbetween1982and1984andhadbeenusedinapreviousevaluation(Cundiffetal.,1990),and14sireswerebornafter1985andusedforthersttimeinCycleVoftheGermplasmEvaluationProjectprogram.ToestimategenetictrendsintheBrahmanbreed,semenfrom16siresbornbetween1984and1989(current)andfrom12siresbornbetween1964and1976(original,Gregoryetal.,1979a)wasusedtoproduceF1intactmaleprogeny.SemenfromsevenBoransireswasimportedfromAustraliaandusedtoproduceF1intactmaleprog-eny.TheBorantracesitsorigintoBosindicusducedfromtheIndiansubcontinentintoEastAfricaabout400A.D.(Hetzel,1988).SemenfromnineTulibullswasimportedfromAustraliaandusedtoproduceF1intactmaleprogeny.TheTuliisabreedindigenoustoEasternandSouthernAfricawitheithernoorminimalBosindicusgermplasm(Frischetal.,1997).BelgianBlue.Semenfrom23sireswasusedtopro-duceF1intactmaleprogeny.TheBelgianBluehashistoricallybeenselectedtoestablishahighfrequencyforamajorgenethatcausesmusclehypertrophy(HansetandMichaux,1985). LunstraandCundiffManagementandDataCollectionBullcalveswereweanedat1851dofage.Followingweaningeachyear,about80bullcalveswererandomlyassignedtotwodrylotpensofapproximately40bullseachwithallsireanddambreedsrepresentedineachpen.Bullswerefedadietofcornsilage,rolledcorn,andprotein-mineral-vitaminsupplement(2.69McalofME/kgofDM,12.88%crudeprotein)for10mo.Aftera42-dacclimationperiod,bodyweight,hipheight,scrotalcircumference,andlengthofeachtesticleweremea-suredat28-dintervalsfor9mo.Alltestismeasure-mentswereperformedbyonetechnicianusingproce-duresasdescribedbyLunstraetal.(1988).Concurrentwiththesemeasurements,electroejaculatedsemencol-lectionswerebegunwhenbullsreachedascrotalcir-cumferenceof26cmandcontinuedat28-dintervals.Ejaculatevolume,spermconcentration,andprogres-sivemotilitywereassessedforeachejaculate,usingthemethodsdescribedbyLunstraandEchternkamp(1982).Briey,semenwasmaintainedat37C,andprogressivemotilitywasdeterminedfromduplicatees-timatesusingamicroscope(400Spermconcentrationwasdeterminedfromspectropho-tometer(550nm)readingsofduplicatesemenaliquotsdiluted1:200with1%formalinin0.9%saline(LunstraandCoulter,1997).Pubertywasdenedastheageatwhichabullrstproducedanejaculatecontainingatleast50spermwith10%progressivemotility(Lunstraetal.,1978).Firstfreezablesemenwasdenedastheageatwhichabullrstproducedanejaculatecontainingatleast500spermwith50%progres-sivemotility(Lunstraetal.,1993),sincethesenumbersrepresentathresholdabovewhichfreezingofsemenbecomeseconomicallyfeasible.After500withatleast50%motilityweredetectedinanejaculate,semencollectionceasedforthatbull.Tocalculatepairedtesticularvolume,scrotalcircumferencewasassumedtorepresenttheconnectedcircumferenceoftwoapposedcirclesofequalradius,r,usingthefol-lowingformula(Lunstraetal.,1988):Noadjustmentforthicknessofthescrotumwasused.Averagetesticularlengthwascalculatedbyaveragingthelengthsoftheleftandrighttesticles.Assumingeachtesticlewasaprolatespheroid,pairedtesticularvolumewasthencalculatedusingthefollowingformula(Lunstraetal.,1988):0.0396(AvgTL)(SC)Approximately14daftercollectionofnaldata,bul

3 lswereslaughtered(~16moofage)atalocalpac
lswereslaughtered(~16moofage)atalocalpackingplant(total136;n75and61bullsbornin1992and1994,respectively;noslaughterdatawerecollectedfrombullsbornin1993).Testesandepididymidesob-tainedatslaughterwereweighed,anda10-gsubsampleoftesticularparenchymawassnap-frozenforsubse-quenthomogenizationtodeterminedailyspermpro-pergramoftestisandtotalDSPperpairedtestes(5.32dwasusedasconstantforDSPcalculations;Amannetal.,1974).SalimandEn-twistle(1982)havesuggestedthataconstantof5.11dshouldbeusedforcalculatingDSPinBosindicusbulls.InitialcalculationandanalysisofDSPandTDSPusingaconstantof5.11dforBrahman-andBoran-siredbullsincreasedtheirDSPandTDSPvaluesbyapproximately4%buthadnosignicanteffectsondif-ferencesamongsirebreeds.Therefore,aDSPconstantof5.32dwasusedforallanalysesinthepresentreport.DataAnalysesDatawereanalyzedwithaleastsquaresprocedure(Harvey,1985),andleastsquaresmeansandSEarepresentedintextandtables.DataforBW,ADG,age,hipheight,testicularmeasurements,ageatpuberty,andpercentagepubescentwereanalyzedwithamodelthatincludedsirebreed,sirenestedwithinsirebreed,dambreed,damage,year,sirebreeddambreed,sireyear,dambreedyear,damageyear,andlineareffectsforbirthdate.Allotherpossibleinterac-tionswereincludedintheinitialanalyses,butinterac-tionswithnonsignicanteffectsweredroppedfromthenalmodel.Levelofsignicanceforinteractionsre-tainedinanalysesisindicatedwithintablesintheRe-sultssection.Sirebreed,dambreed,damage,andyearweretreatedasxedeffects.Allvariables,exceptage,wereadjustedfordifferencesincalendarageusingbirthdateasalinearcovariate.Sirebreedwastestedusingsirenestedwithinsirebreed(sire/sirebreed)asthesourceoferror.Allotherxedeffectsweretestedusingtheresidualerrorvariationforeachtrait.Sirebreedmeansweretestedwithnonorthogonalcontrast.CurrentandoriginalBrahmantypesweretestedwiththesamemodel,butnodifferencesbetweentypeswereobservedforgrowthorpubertytraits,andsubse-quently,bothtypesweretreatedasasingle-sirebreed.Responseswithprobabilitieslessthan0.05wereconsid-eredtobedifferent.Residualcorrelationsamonggrowthandtestistraitsatslaughterwerederivedfromamodelthatincludedthexedeffectsandallinterac-tionsthatweresignicantforatleastonetrait.BirthandWeaningWeightsSirebreedandyearhadsignicanteffectsonbirthweightofF1bulls,butdambreedandthevariousinter-actionshadnosignicanteffects(Table2).Brahman-andBoran-siredbullshadthehighestbirthweights,andTuli-siredbullshadthelowest(0.01),whileHereford-,Angus-andBelgianBlue-siredbullcalveswereintermediate(Table2).Sirebreed,dambreed,damage,year,andtheirinteractionshadnoeffect( BreeddifferencesforpubertyinbeefbullsTable2.LeastsquaresmeansandstandarderrorsforbirthandweaningweightinFbulls(n234)evaluatedforpubertaldevelopmentduring3-yrGermplasmEvaluationProject(CycleV;born1992to1994) Variable SirebreednBirthwt,kgAgeatweaning,dAdjusted200dwt,kgADG(birthtoweaning),kg Hereford3244.11.1185.22.225261.04Angus2443.01.3189.62.525461.06Brahman4749.70.9184.41.726051.06Boran4346.11.1185.81.525471.04Tuli4438.91.0185.41.824261.02BelgianBlue4444.20.9184.12.124451.00AllFbulls23444.40.5185.40.825131.04AveragesirebreedLSD0.052.735.0914.00.07dfProbabilitylevels Sirebreed(SB)50.0010.7550.0690.512Sire/sirebreed970.1820.0800.0020.004Dambreed(DB)20.1290.5500.0060.005Damage30.8460.8060.6850.638Year(Y)20.0050.1140.5490.152DB80.2510.1480.0780.039Y10————DamageY6————Birthdatelinear10.039—0.0060.019 Allmeanswereadjustedfor“agedifferences”byrunningbirthdateasacovariate(i.e.,adjustedtoaverage“age”ofallbulls).Breedgroupdif

4 ferenceslargerthanthesirebreedleastsigni
ferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicant(0.10)onagethatF1bullswereweaned(1851d)inthisstudy(Table2).Brahman-siredbullshadthehighestwhileTuli-andBelgianBlue-siredbullshadthelowestweaningweight(adjusted200-dweight)andlowestADGfrombirthtoweaning;dambreedandsirewithinsirebreedhadsignicanteffectsontheseweightcharacteristics,whiletheeffectofsirebreedap-proachedsignicanceonlyfor200-dweight(Table2).CharacteristicsatInitialMeasurementTheF1bullsaveraged2301dofageatthebegin-ningofevaluationeachyear(Table3),andtherewasnosignicanteffectofsirebreed,dambreed,damage,year,ortheirinteractionsonageofbullsatmonthlyevaluationsthroughoutthestudy.At230dofage,sirebreed,sirewithinsirebreed,dambreed,andyearallhadsignicanteffectsoninitialbodyweightofF1bulls,butdamageandthevariousinteractionshadnosig-nicanteffects(Table3).InitialbodyweightdidnotdifferbetweenAngus-,Hereford-,Brahman-,Boran-,andBelgianBlue-siredF1bullsat230dofage(0.15).However,initialbodyweightofTuli-siredbullswaslessthanHereford-,Angus-,andBrahman-siredbulls(0.01)andlessthanBoran-siredbulls(0.03)butdidnotdifferfromBelgianBlue-siredbulls0.09)at230dofage(Table3).Numerically,initialbodyweightwasheaviestinAngus-andBrahman-siredbulls,intermediateinHereford-,Boran-,andBelgianBlue-siredbulls,andlowestinTuli-siredbullsat230dofage.BullsfromAngus(3094)cowsweighedmoreat230dofage(0.05)thandidbullsfromHereford5)orMARCIII(2904)cows.FixedeffectsinuencedinitialhipheightofF1bullsinamannersimilartoeffectsoninitialbodyweight,exceptthattheeffectofdambreedwasnotsignicant(Table3).Brahman-siredbullsweretaller(0.01)thanotherbreeds,Boran-siredbullsweretaller(0.04)thanTuli-siredbulls,andallotherF1bullswereofsimilarhipheightat230dofage.Allindicatorsoftestissize(SC,AvgTL,andPTV)weresmaller(0.01)inBrahman-andBoran-siredbullsthaninHereford-,Angus-,andBelgianBlue-siredbullsatinitialmeasurement(Table3).TestissizewaslargestinAngus-siredbullsandwassimilaramongHereford-,Tuli-,andBelgianBlue-siredbullsat230dofage.Sirebreedandyearhadconsistentsignicanteffectsonallthreeindicatorsoftestissize(SC,AvgTL,andPTV).Averagetesticularlengthalsowasinuencedbysirewithinsirebreedanddambreed,andPTVwasinuencedbysirewithinsirebreedanddamage(Ta-ble3).CharacteristicsatYearlingMeasurementSirebreed,sirewithinsirebreed,anddambreedhadsignicanteffectsonyearlingbodyweightofF1bulls,andthesirebreedyearanddamageyearinterac-tionsalsohadsignicanteffects(Table4).Angus-andHereford-siredbullsweretheheaviest,whileBrahman-andBelgianBlue-wereintermediate,andBoran-andTuli-siredbullsweighedtheleastatyearlingage.Year-lingbodyweightofTuli-siredbullsdidnotdifferfromBoran-siredbulls(0.11),butbothweighedlessthanAngus-,Hereford-,BelgianBlue-,andBrahman-sired LunstraandCundiffTable3.Leastsquaresmeansandstandarderrorsofvariablesatinitialmeasurement(230dofage)inFbulls(n234)evaluatedforpubertaldevelopmentbetween7and15moofageduringGermplasmEvaluationProject(CycleV) Variableatinitialmeasurement SirebreednAge,dBW,kgHipheight,cmSC,cmAvgTL,cmPTV,cm Hereford32230.22.13026114.10.725.30.48.20.2219Angus24233.52.43077113.40.827.10.58.80.2259Brahman47229.81.73055120.20.621.70.36.70.2134Boran43229.82.32997114.90.822.60.47.00.2148Tuli44229.72.12827113.10.825.40.48.50.2222BelgianBlue44228.81.72945113.20.624.70.38.00.2202AllFbulls234230.30.92983114.80.324.50.27.90.1197AveragesirebreedLSD0.055.115.21.801.010.5326.8dfProbabilitylevels Sirebreed(SB)50.7550.021Sire/sirebreed970.0800.0080.0340.0940.0260.043Da

5 mbreed(DB)20.5500.0050.1450.1010.0100.08
mbreed(DB)20.5500.0050.1450.1010.0100.089Damage30.8060.4080.1490.0940.2070.044Year(Y)20.1140.0010.0180.003DB80.1480.1580.07800.3800.0290.268Y10——————DamageY6—————0.043Birthdatelinear1—0.1650.250.0160.1250.019 scrotalcircumference,AvgTLaveragetestislength,PTVpairedtesticularvolume.Breedgroupdifferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicantbulls(0.01).Angus-andHereford-siredF1bullsdidnotdifferinyearlingbodyweight,butbothAngus-(0.06)andHereford-siredbulls(0.08)tendedtobeTable4.Leastsquaresmeansandstandarderrorsofvariablesatyearlingmeasurement(370dofage)inF234)evaluatedforpubertaldevelopmentbetween7and15moofageduringGermplasmEvaluationProject(CycleV) Variableatyearlingmeasurement ADG(weaningtoHipheight,SirebreednAge,dBW,kgyearling),kgcmSC,cmAvgTL,cmPTV,cm Hereford32370.22.147691.300.03126.10.733.00.411.40.2498Angus24373.52.4481101.330.03125.90.834.40.511.80.2556Brahman47369.81.744371.080.02130.90.630.70.410.70.2409Boran43369.82.3424121.010.04124.60.831.30.510.90.3430Tuli44369.72.1408100.990.03123.80.730.20.410.60.2394BelgianBlue44368.81.745781.230.03126.00.632.40.411.40.2482AllFbulls234370.30.944841.160.01126.20.332.00.211.10.1462AveragesirebreedLSD0.055.0921.20.071.741.110.5248.4dfProbabilitylevels Sirebreed(SB)50.755Sire/sirebreed970.0800.0010.0060.0930.1960.0020.017Dambreed(DB)20.5500.0120.0030.0070.2190.0020.069Damage30.8060.1260.0030.0420.3760.3140.196Year(Y)20.1140.2510.5610.0010.012DB80.1480.1780.2160.5260.8650.6340.714Y10—0.034—————DamageY6—0.0220.0090.010———Birthdatelinear1—0.2030.6020.1310.7830.0870.329 scrotalcircumference,AvgTLaveragetestislength,PTVpairedtesticularvolume.Breedgroupdifferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicant(heavierthanBelgianBlue-siredbulls(Table4).DambreedinuencedF1-bullyearlingweight,andbullsfromAngus(4586)andHereford(4517)cows Breeddifferencesforpubertyinbeefbullsweighedmore(0.05)thandidbullsfromMARCIII6)cows.Ingeneral,differencesinyearlingbodyweightreectedbreeddifferencesinADGfromweaningtoyearlingage;Brahman-,Boran-,andTuli-siredbullsexhibitedthelowestADG,whiletheADGofAngus-,Hereford-,andBelgianBlue-siredbullswashigher(0.01;Table4).Thexedeffectsofsirebreed,sirewithinsirebreed,dambreed,andyearinuencedyear-linghipheightofF1bulls,andtheinteractionofdamyearalsowassignicant(Table4).Brahman-siredbullscontinuedtohavethetallesthipheight(0.01),whileTuli-andBoran-siredbullsweresmallest,andAngus-,Hereford-,andBelgianBlue-siredbullswereofintermediatehipheightatyearlingage(Ta-ble4).Atyearlingage,allindicatorsoftestissize(SC,AvgTL,andPTV)weresmaller(0.05)inBrahman-,Boran-,andTuli-siredbullsthaninbullsofothersirebreeds(Table4).TestissizewaslargestinAngus-siredbulls(0.05),intermediateinHereford-andBelgianBlue-siredbulls,andsmallest(0.05)andrelativelysimilar(0.25)amongBrahman-,Boran-,andTuli-siredbulls.Sirebreedandyearhadconsistentsigni-canteffectsonallthreeindicatorsofyearlingtestissize(SC,AvgTL,andPTV).YearlingAvgTLalsowasinuencedbysirewithinsirebreedanddambreed,andyearlingPTVwasinuencedbysirewithinsirebreed(Table4).CharacteristicsatFinalMeasurementandatSlaughterSirebreed,sirewithinsirebreed,anddambreedhadsignicanteffectsonnalbodyweightofF1bullsat454dofage,andthesirebreedyearanddamageyearinteractionsalsohadsignicanteffects(Table5).Asatyearlingage,Angus-andHereford-siredbullsweretheheaviest,whileBrahman-andBelgianBlue-siredbullswereintermediate,andBoran-andTuli-siredbullsweighedtheleastat454dofage.Fi

6 nalbodyweightofTuli-siredbullsdidnotdiff
nalbodyweightofTuli-siredbullsdidnotdifferfromBoran-siredbulls(0.62),butbothweighedlessthanAngus-,Hereford-,BelgianBlue-,andBrahman-siredbulls(0.01).Angus-andHereford-siredF1bullsdidnotdifferinnalbodyweight(0.32),butbothAngus-0.01)andHereford-siredbulls(0.01)wereheavierthanBelgianBlue-andBrahman-siredbulls(Table5).DambreedinuencedF1-bullbodyweightat454dofage,andbullsfromAngus(5577)cowsweighedmore(0.05)thandidbullsfromHereford(5388)andMARCIII(5247)cows.Similartoresultsatyearlingage,thexedeffectsofsirebreed,sirewithinsirebreed,dambreed,andyearinuencednalhipheightofF1bullsat454dofage,andtheinteractionofdamageyearremainedsignicant(Ta-ble5).Brahman-siredbullscontinuedtohavethetall-esthipheight(0.001),whileTuli-andBoran-siredbullsweresmallest,andAngus-,Hereford-,andBelgianBlue-siredbullswereofintermediateandsimilarhipheightat454dofage(Table5).At454dofage,testissizewasmoresimilaramongbreedsthanatprevioustimepoints.However,allindica-torsoftestissize(SC,AvgTL,andPTV)weresmaller0.02to0.001)inTuli-siredbullsthaninbullsofothersirebreeds(Table5).TestissizewaslargerinAngus-siredbulls(0.06to0.001)thaninotherbreedsexceptHerefordandwasrelativelysimilar(0.25)amongHereford-,Brahman-,Boran-,andBelgianBlue-siredbulls.Sirebreedandsirewithinsirebreedhadconsistentsignicanteffectsonallthreeindicatorsoftestissize(SC,AvgTL,andPTV)at454dofage.FinalAvgTLalsowasinuencedbydambreed,andnalPTVwasinuencedbydambreedanddamage(Table5).Atslaughter(Table6)ofarepresentativeportionofthesebulls(n136)approximately2wkafternalmeasurement,pairedtestesweightandpairedepididy-malweightweresmaller(0.05to0.001)inTuli-siredbullsthaninbullsofothersirebreeds.PairedtestesweightwaslargerinAngus-siredbulls(to0.001)thaninTuli-,Boran-,andBelgianBlue-siredbulls.Pairedtestesweightandpairedepididymalweightwererelativelysimilar(0.25)amongAngus-andHereford-siredbulls,amongBrahman-andBoran-siredbulls,andamongBelgianBlue-andTuli-siredbulls(Table6).WhileDSPpergramoftestisdidnotdiffer(0.06)amongsirebreedgroups(Table6),TDSPwasmarkedlylowerinTuli-siredbulls(to0.001)thaninbullsofothersirebreedsexceptBel-gianBlue-siredbulls(0.15).Thus,sirebreeddiffer-encesinTDSPreectedthemajordifferencesinpairedtestisweightamongsirebreeds.Spermproduction(DSPandTDSP)inBelgianBlue-siredbullsdidnotdiffer(0.15)fromthatofbullsofanyothersirebreeds(Table6).Residualcorrelationsindicatedthatpairedtestesweightatslaughterhadlittlerelationshiptobullbodyweightandhipheight,butpairedtestesweightwaswellcorrelatedwithTDSP(r0.65)andhighlycorrelatedwithliveanimalmeasurementofscro-talcircumference(r0.84)andestimatesofpairedtestesvolume(r0.87).Sincetestisweightandspermproductionwerehighlycorrelatedtoliveanimaltestesmeasurements,thesignicanceofstatisticalxedef-fectswerereectedatnalmeasurement(Table5)andarenotpresentedagainhere.CharacteristicsatPubertyAtpuberty,largebreeddifferencesinage,bodyweight,andhipheightwerepresent(Table7).Angus-siredbullswere23to82dyoungeratpubertythanwerebullsofallothersirebreeds,whichwasearlier0.05to0.001)thaninanyotherbreedexceptHereford(0.09),andBrahman-siredbullswereolderatpuberty(0.05to0.001)thanwerebullsofallothersirebreedsexceptBoran(0.08).Withtheirolderageatpuberty,Brahman-siredbullsweretallerandheavieratpuberty(0.01to0.001)thanwerebullsofallothersirebreeds,andBoran-sired LunstraandCundiffTable5.LeastsquaresmeansandstandarderrorsofvariablesatÞnalmeasurement(454dofage)inFbulls(n234)evaluatedforpubertaldevelopmentbetween7and15moofageduringGermplasmEvaluat

7 ionProject(CycleV) Variableatnalmeasure
ionProject(CycleV) Variableatnalmeasurement SirebreednAge,dBW,kgHipheight,cmSC,cmAvgTL,cmPTV,cm Hereford32454.52.057510128.80.835.70.511.50.2587Angus24457.32.359112128.30.936.20.611.90.2618Brahman47453.91.65329135.00.735.00.411.30.2550Boran43453.82.050014127.20.934.70.511.50.2549Tuli44453.81.949412127.30.833.10.510.90.2478BelgianBlue44452.82.154711129.30.834.90.511.10.2542AllFbulls234454.30.95405129.30.434.90.211.40.1554AveragesirebreedLSD0.055.0425.82.041.180.4954.0dfProbabilitylevels Sirebreed(SB)50.7810.0010.012Sire/sirebreed970.1880.0010.0320.0250.0010.004Dambreed(DB)20.4020.0030.0100.2640.0060.043Damage30.6670.0630.1330.0150.1300.025Year(Y)20.0920.3630.0280.3620.1150.267DB80.1740.0590.5190.5340.5790.388Y10—0.052————DamageY6—0.0100.029———Birthdatelinear1—0.3030.0680.8070.3460.643 scrotalcircumference,AvgTLaveragetestislength,PTVpairedtesticularvolume.Breedgroupdifferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicantTable6.Leastsquaresmeansandstandarderrorsofvariablesatslaughter(n136;470dofage)inFevaluatedforpubertaldevelopmentbetween7and15moofageduringGermplasmEvaluationProject(CycleV) Variableatslaughter Pairedtestesweight,PairedepididymalDailyspermTotaldailyspermSirebreednSlaughterage,dgwt,gproduction/g Hereford22470.92.05682358.21.910.40.75,637Angus15471.72.36092657.72.39.90.85,836Brahman28470.41.65641950.91.79.40.65,144Boran29470.82.05431952.11.69.60.65,059Tuli29470.31.94261944.31.68.70.63,657BelgianBlue13469.12.14952948.62.510.30.94,611AllFbulls136470.60.95292551.42.09.60.54,914AveragesirebreedLSD0.055.0646.21.81,280Residualcorrelations(allbulls)Finalbodywt0.1710.3470.3420.0780.127Finalhipheight0.2720.1730.238Finalscrotalcircumference0.0200.8390.6750.0780.477Finalpairedtestesvolume0.2200.8700.6850.0530.480Slaughterage—0.0520.092Pairedtesteswt——0.7640.2010.651Pairedepididymalwt———0.1680.517Dailyspermproduction/g————0.845Totaldailyspermproduction————— Obtainedatslaughterat470dofage.ExpressedasspermproductionBreedgroupdifferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicant(Pearsonresidualcorrelations,afteranalysistoremovetheeffectsofsire,sirebreed,dambreed,year,ageofdam,andappropriateinteractions(Obtainedat454dofage.SeeTable5(i.e.,nalliveanimalmeasurement). BreeddifferencesforpubertyinbeefbullsTable7.Leastsquaresmeansandstandarderrorsofvariablesatpuberty(50spermwith10%progressivemotility)inFbulls(n234)evaluatedforpubertaldevelopmentbetween7and15moofageduringGermplasmEvaluationProject(CycleV) Variableatpuberty ADG(weaningtoHipheight,SirebreednAge,dBW,kgpuberty),kgcmSC,cmAvgTL,cmPTV,cm Hereford32261933991.380.17117.11.027.90.29.40.1293Angus2423810323111.890.17114.21.128.10.29.40.2292Brahman47320739181.130.14127.70.827.90.19.60.1298Boran43302836291.100.25120.61.327.80.19.60.1296Tuli44284833191.090.21117.41.127.70.19.60.1294BelgianBlue44273734781.380.10117.60.927.90.19.60.1297AllFbulls234279434941.330.08119.10.527.90.19.50.1295AveragesirebreedLSD0.0521.723.00.392.490.310.3213.8dfProbabilitylevels Sirebreed(SB)50.0010.0080.0010.6230.7560.958Sire/sirebreed970.2880.2170.0010.0140.9810.0890.348Dambreed(DB)20.0980.3820.2570.7850.8220.0520.419Damage30.5640.1790.2840.0990.8630.1270.237Year(Y)20.2050.2580.0020.4800.628DB80.9360.9410.8600.9720.7750.4610.316Y10——0.002————DamageY6———————Birthdatelinear10.2300.8050.7970.2870.7920.9450.839 Pubertyoccurredwhenabullrstproducedanejaculatecontainingatleast50spermwith10%progressivemotility.scrotalcircumfer

8 ence,AvgTLaveragetestislength,PTRpairedt
ence,AvgTLaveragetestislength,PTRpairedtesticularvolume.Breedgroupdifferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicant(bullsweretallerandheavieratpuberty(0.05to0.001)thanwerebreedsotherthanBrahman(Table7).Hereford-,Tuli-,andBelgianBlue-siredbullsweresimilarinage,bodyweight,andhipheightatpuberty(Table7).Ingeneral,differencesinbodyweightatpubertyreectedbreeddifferencesinADGfromwean-ingtopuberty;Brahman-,Boran-,andTuli-siredbullsexhibitedthelowestADG,whiletheADGofotherbreedstendedtobehigher,andAngus-siredbullshadthehighestADG(0.05to0.001;Table7).OnlysirebreedhadasignicanteffectonageatpubertyandbodyweightatpubertyinF1bulls(Table7),whilesirebreedandsirewithinsirebreedhadsignicanteffectsonADGandhipheightatpuberty.Atpuberty,denedastheagewhenabullrstpro-ducedanejaculatecontainingatleast5010%progressivemotility,neithersirebreednorsirewithinsirebreedhadanyeffectontestissize,andthemeansforSC,AvgTL,andPTVatpubertyeachwereverysimilar(0.21)amongbreeds(Table7).Scrotalcircumferenceatpubertywasnotinuencedbyanyxedeffectsorinteractions,andyearwastheonlyfactorthathadasignicanteffectonAvgTLatpubertyandPTVatpuberty(Table7).Scrotalcircumferenceatpubertyaveraged28cminallsirebreedgroups.Sincesirebreedwastheonlyxedeffectthatinu-encedageatpubertyinF1bulls,sirebreeddifferencesinthepatternsofpubertaldevelopmentinF1bullsareshowninFigure1.AgreaterproportionofAngus-siredF1bullshadreachedpubertyby7,8,and9moofagethaninothersirebreeds(Figure1).TheAnguspatternwasfollowedcloselybyHereford-siredbulls,and100percentofAngus-andHereford-siredbullswerepubes-centby11moofageandbeyond.Brahman-andBoran-siredbullsweretheslowesttoreachpuberty,andtheproportionpubertallaggedbehindthatofAngus-,Here- 6789101112131415Age, mo Angus Hereford BelgianBlue Tuli Boran Brahman l ve percentageof pubertal bulls Figure1.Graphiccomparisonofthedifferencesamongsixsirebreedsinproportions(patternsofcumulativepercentagebecomingpubescent)ofFbeefbullsreachingpuberty(deÞnedastheageatwhichabullÞrstproducedanejaculatecontainingatleast50spermwithprogressivemotility).Datawereobtainedfrom234Fbullsevaluatedmonthlyfromweaningthrough15moofageandthenumberofFbullsevaluatedpersirebreedrangedfrom24to47. LunstraandCundiffTable8.Leastsquaresmeansandstandarderrorsofvariablesatfreezablesemen(500spermwithprogressivemotility)inFbulls(n234)evaluatedforpubertaldevelopmentbetween7and15moofageduringGermplasmEvaluationProject(CycleV) Variableatfreezablesemen ADG(weaningtoHipheight,SirebreednAge,dBW,kgfreezablesemen),kgcmSC,cmAvgTL,cmPTV,cm Hereford3232610420121.300.03122.40.931.40.410.80.2428Angus2431111409141.350.03121.01.032.00.510.80.2442Brahman473988469101.090.03131.80.832.40.311.00.1464Boran4338111434141.000.04124.91.131.90.510.90.2442Tuli4436210400130.980.03123.11.030.40.510.40.2384BelgianBlue443258407111.260.03122.60.830.80.410.80.1410AllFbulls234350442351.160.01124.30.431.50.210.80.1429AveragesirebreedLSD0.0524.530.40.072.281.030.4141.7dfProbabilitylevels Sirebreed(SB)50.0010.0010.0010.0010.0590.003Sire/sirebreed970.0280.0220.0050.0170.0010.008Dambreed(DB)20.1980.6090.0150.5270.3040.0130.115Damage30.8670.2110.0060.2090.3200.0570.126Year(Y)20.0020.0090.0010.1740.064DB80.4720.7860.4230.6640.8770.7590.818Y10——0.001————DamageY6——0.006————Birthdatelinear10.0260.8680.2340.0940.3480.1770.129 Pubertyoccurredwhenabullrstproducedanejaculatecontainingatleast50spermwith10%progressivemotility.scrotalcircumference,AvgTLaveragetestislength,PTRpairedtesti

9 cularvolume,ADGaveragedailygain.Breedgro
cularvolume,ADGaveragedailygain.Breedgroupdifferenceslargerthanthesirebreedleastsignicantdifference(LSD0.05)aresignicant(ford-,andBelgianBlue-siredbreedsthrough12moofage(0.05;Figure1).TheproportionofBelgianBlue-siredbullsreachingpubertywassomewhatlowerthanthatofAngus-andHereford-siredbullsthrough11moofage,buttheproportionpubescentwasmoresimilartothatofAngus-andHereford-siredbullsthantootherbreeds.ThepatternofpubertaldevelopmentinTuli-siredbulls(bulls)appearedtobeintermediatetothetwopatternsdisplayedbyBostaurus-and-siredbulls.CharacteristicsatFirstFreezableSemenAtrstfreezablesemen,asatpuberty,largebreeddifferencesinage,bodyweight,andhipheightwereobserved(Table8).Angus-siredbullswere24to87dyoungeratfreezablesemen,whichwasearlier(0.001)thanotherbreedsexceptHereford-(andBelgianBlue-siredbulls(0.30).Brahman-siredbullswereolderatfreezablesemen(0.01)thanwerebullsofallothersirebreedsexceptBoran(Withtheirolderageatfreezablesemen,Brahman-siredbullsweretallerandheavieratfreezablesemen(0.02to0.001)thanwerebullsofallothersirebreeds.Boran-siredbullsweretalleratfreezablesemen(0.04to0.001)thanwerebreedsotherthanBrahman(Table8),butbodyweightatfreezablesemeninBoran-siredbullsdidnotdifferfromthatofHereford-(0.35)andAngus-siredbulls(0.15).Hereford-andBelgianBlue-siredbullsweresimilarinage,bodyweight,andhipheightatfreezablesemen(Table8).Boran-andTuli-siredbullshadlowerADGfromwean-ingtofreezablesementhandidBrahman-(0.01)andotherbreeds(0.001),whiletheADGofHereford-,Angus-,andBelgianBlue-siredbullsweresimilarandhigherthanthatofotherbreeds(0.001;Table8).Sirebreed,sirewithinbreed,andyearhadsignicanteffectsonageandbodyweightatfreezablesemeninF1bulls(Table8),whileonlysirebreedandsirewithinsirebreedhadsignicanteffectsonhipheightatfreeza-blesemen.Atrstfreezablesemen,denedastheagewhenabullrstproducedanejaculatecontainingatleast500spermwith50%progressivemotility,severalxedeffectsinuencedtestissizeinF1bulls.Sirebreed,sirewithinsirebreed,andyearallhadsignicantef-fectsonmeanSC,AvgTL,andPTVatfreezablesemen(Table8).MeanSC,AvgTL,andPTVatfreezablesemeneachwereverysimilaramongAngus-,Brahman-,andBoran-siredbulls(0.30),slightlysmallerinHere-ford-andBelgianBlue-siredbulls,andsmallestinTuli-siredbulls(Table8).Scrotalcircumference,AvgTL,andPTVatfreezablesemenwerenotinuencedsigni-cantlybyanyinteractions(Table8).IntheU.S.beefcattleindustry,sourcesoftropicallyadaptedgermplasmhavebeengenerallylimitedtoZebubreeds(Bosindicus,cattlewithaprominenttho-racichumpthatoriginallyevolvedinsouthernAsia),primarilytotheAmericanBrahman(Chaseetal., Breeddifferencesforpubertyinbeefbulls2001).Currently,about37%ofallbeefcowsintheUnitedStatesaremaintainedinstressfulsubtropicalenvironmentswhere25to50%Bosindicus(primarilyBrahman)isrequiredtoprovideforefcientproduction(Cundiffetal.,1986,2000).BosindicusBostauruscrosscattleexcelinweaningweightpercowexposed(Cundiffetal.,1986)andincowefciency(Greenetal.,1991),becauseofhigherheterosisrelativeBosindicusBostauruscrosses.However,astheproportionofBosindicusinheritanceincreases,thead-vantagesofBrahmaninuenceonheterosisandcompo-nentsofcowefciencyaretemperedbyolderageatpuberty(Gregoryetal.,1979b;Chenowethetal.,1996;Cundiffetal.,2000),discountsforreducedmarblingofbeef(Wheeleretal.,1994;Franke,1997),andreducedmeattenderness(Wheeleretal.,1994;2001;Franke,1997;O’Connoretal.,1997).Towardthisend,furthergermplasmevaluationisneededtoidentifynewbreedsthatmaintainproductionadvantageswhilereducingtheseproblems.Thus,w

10 ethoughtitwasappropriatetoinvestigatemal
ethoughtitwasappropriatetoinvestigatemalereproductivedevelopmentinbreedsthatmayprovideincreasedmarblingandmusclingandtodetermineifadditionalBosindicusbreeds(cattlewithaprominentcervicalhump)thatevolvedundertropicalconditionsinAfricasharethesamemalereproductivecharacteristicsasthosewhichhaveevolvedinsouthernAsia.Thesiresfromthesirebreedsusedinthisstudy(Hereford,An-gus,BelgianBlue,Brahman,Boran,andTuli)wereselectedtorepresentthepredominantgeneticsofeachbreed.Thus,theresultsprovideacurrentcomparisonofmalereproductivedevelopmentinbullsrepresentingthesediversebreeds.Atbirth,Brahman-siredbullcalvesweighed5.3to6.7kgmore,Boran-siredcalvesweighed1.7to3.1kgmore,andTuli-siredcalvesweighed4.1to5.5kgless,thandidHereford-,Angus-,andBelgianBlue-siredbullcalves.TheheavierbirthweightsofZebu-siredcom-paredtoBostaurus-siredbullcalvesagreeswellwithpublisheddata.OthershavereportedthatprogenyofBrahmansiresare3to6kgheavier,progenyofBoransiresareslightlyheavier,andprogenyofTulisiresare2to4kglighterinbirthweightthanareprogenyofBostaurussires(Browningetal.,1995;Herringetal.,1996;Thrift,1997).Therelationshipsbetweenthesesirebreeddifferencesinbirthweightweremaintainedatweaning.Atweaning,Brahman-siredbullsweighed6to16kgmore,Boran-siredbullsweighed0to10kgmore,andTuli-siredbullsweighed2to12kgless,thandidHereford-,Angus-,andBelgianBlue-siredbulls.Again,thesebreeddifferencesinweaningweightagreewellwithdatainpreviousreports(Browningetal.,1995;Herringetal.,1996;Thrift,1997;Cundiffetal.,1998;Chaseetal.,2000).BullsfromHerefordcows1.1)tendedtohavelowerbirthweights(0.13)thandidbullsfromAngus(44.50.9)andMARCIII(45.90.9kg)cows,andbullsfromHereford(1.000.02)andMARCIII(1.020.02)cowshadlowerratesofgainfrombirthtoweaning(0.05)thandidbullsfromAnguscows(1.090.02kg).Thus,therewasaninteractionbetweensirebreedanddambreed(forADGfrombirthtoweaning,butthisinteractionexhibitednootherapparentormeaningfultrend.By230dofage,bodyweightdidnotdifferbetweenAngus-,Hereford-,Brahman-,Boran-,andBelgianBlue-siredF1bulls,butbodyweightinTuli-siredbullsremainedsignicantlylowerthaninotherbreeds.De-spitetheirlowerbodyweight,Tuli-siredbullsdidnotdifferinhipheightfromAngus-,Hereford-,andBelgianBlue-siredbullsat230dofage.However,Brahman-siredbullsweresubstantiallytaller(5to7cm)thanotherbreedsat230dofage,andBoran-siredbullsweresignicantlytaller(~2cm)thanTuli-siredbulls.OthershavereportedthathipheightsofTuli-siredcalvesare7to9cmshorterthanBrahman-siredcalvesatweaningbutaresimilartoorlessthanhipheightsofBostaurussiredcalves(Herringetal.,1996;Browningetal.,1997;Chaseetal.,2000).Dramaticdifferencesintestissizewerepresentamongsirebreedsatinitialmeasurement.Scrotalcir-cumferenceinBrahman-andBoran-siredbullswas2to4cmsmallerthaninTuli-,BelgianBlue-,andHereford-siredbullsand4to6cmsmallerthaninAngus-siredbullsat230dofage.TesticularlengthandPTVexhib-itedsirebreedeffectssimilartodifferencesinscrotalcircumference,andPTVinZebu-siredbullswasapprox-imatelyone-halfthatofAngus-siredbulls,whilePTVwasintermediateinTuli-,BelgianBlue-,andHereford-siredbulls.Whencastratedat205to223dofageinTexas,pairedtestesweightinAngus-siredbulls(734g)wastwicethatofBrahman-siredbulls(374g),andthatofTuli-siredbullswasintermediate(433g;Browningetal.,1997).BullsintheirstudyhadBrah-mandamsandhadsubstantiallysmallertestesthandidbullsinourstudyatsimilarages.InFlorida,scrotalcircumferenceat249dofageinBrahmanAngusbullswassmaller(20cm)thaninTuliAngusbulls(22cm;Chaseetal.,2001)andagreeswellwithdataobtainedinour

11 studyforBrahman-siredbulls(22cm)atinitia
studyforBrahman-siredbulls(22cm)atinitialmeasurement.BullsinTexas(Browningetal.,1997)alsoweighed70to130kglessthanbullsinourstudyandweighed33to74kglessthanbullsinFlorida(Chaseetal.,2000).InanotherstudyinTexas(Herringetal.,1996),bodyweightatweaning(7mo)ofF1calves(bothsexes)siredbyBrahman,Boran,andTulibullsandborntoHerefordandAnguscowswassimilartothatreportedinFloridabutremained74to82kglowerthanthatofcomparablebreedtypesinourstudy.Tropi-caladaptation(heat-tolerance)isassociatedwithre-ducedtestissizeinBosindicuscattle(Fieldsetal.,1979,1982;Godfreyetal.,1990;Randel,1994;Chaseetal.,1997)andmaybepartoftheexplanationforthesmallertestissizeofbullsinTexas.Inaddition,climatemayhavehadadetrimentaleffectongrowthandtestisdevelopmentofZebu-crossbullsinTexas.Asevidencedbysirebreeddifferencesinbodyweightatyearlingageandatnalmeasurement(454dofage),Bostaurus-siredbullsgrewmorerapidlyafterweaning LunstraandCundiffthandidBrahman-,Boran-,andTuli-siredbulls.ThisisbestreectedbycomparisonofsirebreeddifferencesinADGfromweaningtoyearlingage;theADGofallBostaurus-siredbullgroupswererelativelysimi-larandsignicantlyhigherthantheADGofBrahman-,Boran-,andTuli-siredbulls.Theseresultsareconsis-tentwithotherreportsongrowthratesandbodyweightsforthesebreedtypes(Herringetal.,1996;FreetlyandCundiff,1997;Chaseetal.,2001)andsub-stantiatethehypothesisthatoffspringofheat-adaptedsirebreedshavelowerratesofgainandfeedefcienciesthandooffspringofnonheatadaptedsirebreeds(FreetlyandCundiff,1997).Thesedifferencesingrowthpatternsthroughyearlingagemaybepartiallyattrib-utabletoseasonaleffectsthatfavorheat-adaptedbreedsduringthepreweaningperiod(predominantlysummermonths;ApriltoSeptember)butfavoringcold-tolerantbreedsduringthepostweaningperiod(pre-dominantlywintermonths;OctobertoMarch).Previ-ouscomparisonsofbreedsthatevolvedintemperatevstropicalclimateshaveshownasimilareffectofsea-sonongrowthofsteers(Cundiffetal.,1984)andheifers(Gregoryetal.,1979a,1979b;FreetlyandCundiff,1997;Thallmanetal.,1999)borninspringmonths.Testissizewassmallerinoffspringofheat-adaptedsirebreedsthroughyearlingagebuthadbecomesimi-laramongHereford-,Brahman-,Boran-,andBelgianBlue-siredbullsby454dofage.However,testissizeinTuli-siredbullsremainedsmallerthaninbullsofothersirebreedsthrough454dofage,andtestissizeandTDSPinTuli-siredbullsremainedsmalleratslaughter.Thus,offspringofheat-adaptedsirebreedshavesubstantiallysmallertestesat7moofageandexhibitdelayedtesticulardevelopmentcomparedtooff-springofnonheatadaptedsirebreedsatleastthroughyearlingage.Relativelyrapidtesticulargrowthoc-curredinoffspringofheat-adaptedsirebreedsbetween12and15moofage.Whiledifferencesinyearlingtestissizeprimarilyreectbreeddifferencesinageatpu-berty,postpubertaltestisgrowthappearstobemorerapidinoffspringofheat-adaptedsirebreeds.Acceler-atedpostpubertaltestisgrowthinheat-adaptedbreedsmayberelatedtoseasonaleffectsonbodygrowththatfavorheat-adaptedbreedsduringthepostyearlingpe-riod(predominantlysummermonths;ApriltoJuly).Alternatively,thehighlevelofheterosisinBosindicusBostaurusoffspring(Koger,1980;Greenetal.,1991;Gregoryetal.,1991,1997a,b;Cundiffetal.,1986,2000)mayhaveimprovedtesticulargrowth(Gregoryetal.,1991)enoughinBrahman-andBoran-siredoffspringtooffsetthedetrimentaleffectofheat-tolerance.Furtherresearchisneededtoclarifythepotentialeffectsofthesefactorsontesticulardevelopment.Inthecurrentstudy,bullsfromheat-adaptedsirebreedsreachedpuberty11to82dlaterandproducedfreezablesemen36to87dlaterthandidbullsfromnonh

12 eatadaptedsirebreeds.Breeddifferencesfor
eatadaptedsirebreeds.BreeddifferencesforageatpubertyingeneticallyrelatedAngus-,Hereford-,Bel-gianBlue-,Brahman-,Boran-,andTuli-siredheifersatClayCenter(FreetlyandCundiff,1997)wereverysimilartotherelativebreeddifferencesinbullageatpuberty.Also,theolderageatpubertyinbullsandheiferssiredbyheat-adaptedbreedscomparedtonon-adaptedbreedsagreeswiththeolderpubertalagere-portedforBrahman-andSahiwal-siredheifers(Greg-oryetal.,1979b)andBrahman-andSahiwal-siredbulls(Lunstraetal.,1993).Thus,datainthecurrentstudysupporttheconceptthatbreeddifferencesinageatpubertyappeartobeofsimilarmagnitudeinbothmalesandfemales,eveninwidelydivergentbeefbreeds(Lun-straetal.,1988;Gregoryetal.,1991;FreetlyandCun-diff,1997).However,Tuli-andBoran-siredbullsreachedpubertyearlierthandidBrahman-siredbulls,suggestingthatearlierpubertycanbeachievedinsomeheat-adaptedbreedsofcattle.Atpuberty,testissizewasquitesimilaramongbreedsofbulls,despitethelargebreeddifferencesinage,bodyweight,andhipheightthatwerepresentatpuberty.Regardlessofsirebreed,bullsreachedpubertywhenscrotalcircumferencereachedapproximately28cm,andPTVreachedapproximately300cm.WehaveshownpreviouslythatZebuBostaurusbullsandbullsBostaurusbeefbreedsreachpubertyat28cmscrotalcircumference(Lunstraetal.,1978,1988,1993;God-freyetal.,1992).Consistentwiththepresentresults,otherresearchershavereportedthatBrahman-,Ro-mosinuano-,Nellore-,Senepol-,andTuli-siredbullsreachpubertyat27to31cmscrotalcircumference(Chaseetal.,1997,2001).Sincetestissizeatpubertydoesnotvaryamongbreedtypesofbullsthatexhibitmarkeddifferencesinageatpuberty,andscrotalcir-cumferenceinyearlingbeefbullsishighlyheritable(h0.41to0.430.06;Latimeretal.,1982;Lunstraetal.,1988;Gregoryetal.,1991)andisstronglycorrelatedwithageatonsetofpubertyinbeefbulls(r0.64to0.80;Lunstraetal.,1978;1988;LunstraandEchtern-kamp,1982)andingeneticallyrelatedfemales(Luns-traetal.,1988;Gregoryetal.,1991;FreetlyandCun-diff,1997),measurementofyearlingscrotalcircumfer-enceisrecommendedasausefultoolforassessingandpredictingageatpubertyamongandwithinbullsofwidelydivergentbreedtypes.Consistentwithpreviousreportscharacterizinggrowthandpubertaldevelopmentinfemalesofthesebreeds,resultsofthisstudydemonstratedthatmaleoffspringofdiverseheat-adaptedsirebreedshadlowerpostweaninggrowthratesandwereslowertoreachpubertythanwereoffspringofEuropeansirebreeds.Inaddition,measurementofyearlingtestissizewasareliableindicatorofageatpubertyamongwidelydivergentbreedsofbulls.Thus,producersusingheat-adaptedbreedsneedtoemphasizegrowthrateandear-lierpubertaldevelopmentingeneticimprovementpro-gramsforheat-tolerantbreedsandmayneedtoplaceaddedemphasisonthesetraitsinselectionofbreeds BreeddifferencesforpubertyinbeefbullsforuseincrossbreedingprogramsorindevelopmentofcompositepopulationsadaptedtosubtropicalclimaticenvironmentsintheUnitedStates.LiteratureCitedAmann,R.P.,J.F.Kavanaugh,L.C.Griel,Jr.,andJ.K.Vogelmayr.1974.SpermproductionofHolsteinbullsdeterminedfromtestic-ularspermatidreserves,aftercannulationofretetestisorvasdeferens,andbydailyejaculation.J.DairySci.57:93–99.Arthur,P.F.1995.Doublemusclingincattle:Areview.Aust.J.Agric.Res.46:1493–1515.Browning,R.,Jr.,M.L.Leite-Browning,D.A.Neuendorff,andR.D.Randel.1995.PreweaninggrowthofAngus-(Bostaurus),(Bosindicus),andTuli-siredcalvesandre-productiveperformanceoftheirBrahmandams.J.Anim.Sci.Browning,R.,Jr.,B.G.Warrington,J.W.Holloway,andR.D.Randel.1997.Testicularsizeatweaningintropically-adaptedbeefbullsasinuencedbybreedofsireanddam.Theri

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