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Application of multivariate principal component analysis to morphological characterization of indigenous goats in Southern Nigeria

Application of multivariate principal component analysis to morphological characterization of... doi:10.2478/v10014-011-0026-4 COBISS:1.01 Agriscategorycode:L01 MosesOKPEKU1,2,#,AbdulmojeedYAKUBU3,#,SundayOlusolaPETERS2,4, MichaelOhiokhuaoboOZOJE2,ChristianObioraNdubuisiIKEOBI2, OlufunmilayoAyokaADEBAMBO2,IkhideGodwinIMUMORIN4,* ReceivedJuly22,2011;acceptedSeptember15,2011. Delojeprispelo22.julija2011,sprejeto15.septembra2011. Application of multivariate principal component analysis to morphological characterization of indigenous goats in South ern Nigeria Phenotypicvariationpresentinapopulationarisesdueto genotypicandenvironmentaleffects,andthemagnitudeofphenotypic variability differs under different environmental conditions, therefore, the purpose of this study was to objectively describethelineartypetraitsofextensivelymanagedmatureindigenousgoats ofSouthernNigeria andtopredict bodyweight from their orthogonal shape characters using principal componentanalysis.Bodyweightandfourbodymeasurements namely, height at withers, neck length, body length and heart girth were measured in 265 randomlyselectedWestAfricanDwarf(WAD) andRedSokoto(RS)goatsofbothsexes.RSgoatshadsignificantly(P<0.05)highermorphologicaltraitscomparedtotheirWAD counterparts. Sexual dimorphism was observed in all the traits with higher values recorded for males. Phenotypic correlations amongbodyweightandbiometrictraitswerepositiveandhighly significant(r=0.76­0.91versus0.82­0.97and0.66­0.94versus 0.83­0.91forWADandRSfemaleandmalegoats,respectively). Inthevarimaxrotatedprincipalcomponentfactoranalysis,two factors were extracted for each sex of the two breeds, although with varying degrees of factor loadings. The principal componentbasedregressionmodels,whicharepreferableforselecting animalsforoptimalbalance,accountedfor89.00and96.00%as well as 81.00 and 91.00% of the variation in body weight of femaleandmaleWADandRSgoats,respectively.Theinformation obtainedcouldbeusefulindesigningappropriatemanagement, selectionandbreedingprogrammesforutilizationofgoatgenetic resources. Key words: goats / autochthonous breeds / body traits / multivariateanalysis/Nigeria 1 2 3 4 # * Uporaba multivariatne analize glavnih komponent pri morfoloski karakterizaciji avtohtonih koz v juzni Nigeriji Fenotipska variabilnost v populaciji je pogojena z delovanjemgenetskihinokoljskihdejavnikov.Kerjeobsegfenotipske variabilnostirazlicenvrazlicnihokoljih,smoskusalivtejstudiji objektivno predstaviti linearne eksterierne lastnosti ekstenzivnovzrejanihavtohtonihkozvjuzniNigerijiinzanalizoglavnih komponentnapovedatitelesnomasonaosnovilastnosti,kiopredeljujejonjihovotelesnoobliko.Izmerilismotelesnomasoinstiri telesnemere(visinavvihru,dolzinavratu,dolzinatrupainobsegprsi)pri265nakljucnoizbranihzahodnoafriskihpritlikavih kozah(WestAfricanDwarf,WAD)inrdecihsokotokozah(Red Sokoto,RS)obehspolov.Vrednostizamerjenelastnostisobilepri RSkozahstatisticnoznacilno(p<0,05)vecjekotpriWADkozah. Spolni dimorfizem smo zabelezili pri vseh lastnostih, z vecjimi vrednostmizasamce.Fenotipskekorelacijemedtelesnomasoin biometricnimi lastnostmi so bile pozitivne in statisticno visoko znacilne(r=0,76­0,91in0,82­0.97ter0,66­0,94in0,83­0,91za WADinRSzivalizenskegatermoskegaspola).SfaktorskoanalizozVarimaxrotacijosmozavsakoodobehpaseminvsakspol dobilipodvafaktorja.Regresijskimodeli,kitemeljijonaanalizi glavnih komponent in so primerni za selekcijo zivali, so pojasnili89,00in96,00%,ter81,00in91,00%variancetelesneteze zenskihinmoskihzivalipasemWADinRS.Zbraneinformacije bodo uporabne pri upravljanju, selekciji in nacrtovanju rejskih programovzaboljseizkoriscanjegenskihvirovprikozah. Kljucne besede: koze / avtohtone pasme / telesne mere / multivariantnaanaliza/Nigerija NigerDeltaUniv.,Dept.ofLivestockProductionWilberforceIsland,P.M.B.071,Amassoma,BayelsaState,Nigeria Univ.ofAgriculture,Dept.ofAnimalBreedingandGenetics,Abeokuta,P.M.B.2240,Abeokuta,Nigeria NasarawaStateUniv.,Dept.ofAnimalScience,Fac.ofAgriculture,LafiaCampus,P.M.B.135,Lafia,Nigeria CornellUniv.,Dept.ofAnimalScience,267MorrisonHall,Ithaca,NY14853,USA Bothauthorscontributedequallytothispaper. Correspondence: Dr. Ikhide Godwin Imumorin, Dept. of Animal Science, Cornell Univ., Ithaca, NY 14853, USA, Tel: +1 607-255-2850, Fax: +1 607-255-9829, E-mail:igi2@cornell.edu Acta argiculturae Slovenica, 98/2, 101­109, Ljubljana 2011 INTRODUCTION Livestock of different species fulfill different functionsinthehouseholdeconomyandpoorfamiliesoften keep a diversity of species for this reason (Anderson, 2003). Domestic goats (Capra hircus, L.) are important andadaptabledomesticatedanimals(AbdelAziz,2010). Theyprovideafullrangeofusefulproductstohumans includingmeat,milk,skinandhair.Theyefficientlysurviveonavailableshrubsandtreesinadverseharshenvironmentandinlowfertilitylandswherenoothercrops canbegrowninNigeria.Goatproductionovertheyears isoneofthemajormeansofimprovingthelivelihoods ofpoorlivestockkeepers,reducingpovertyandattaining sustainableagricultureanduniversalfoodsecurity(AbdelAziz,2010).ThepopulationofgoatsinNigeriaisestimatedat53.8million(FAOSTAT,2011)ofwhichtraditionallyrearedstockcontributes99.97%,while0.03%of thestockiscommerciallymanaged.Basedonmorphology, the two most important goat breeds traditionally recognized in Nigeria are the Red Sokoto (RS) and the WestAfricanDwarf(WAD)goats,respectively(Ebozoje and Ikeobi, 1998). The WAD goat, which is trypanotolerant,isnativetothesouthernrainforestandderived savanahzoneswhiletheRSgoat,highlyreputedforits quality skin (found more in the northern axis) is more widelydistributedacrossthecountry. The diversity in gene pool and influence of varied climatic conditions have given rise to different local populations of goats which are repositories of unique genes that should be conserved for local and international future benefits (Adebambo, 2004). According to Groeneveldet al.(2010),identifyingandunderstanding auniquegeneticresourceinaparticularregionandthe development andproperuseof theassociateddiversity isaglobalresponsibility.Breedcharacterizationhasaccordingly been recognized as the first approach to the sustainableuseofanimalgeneticresource(Lanariet al., 2003). It is believed that various breed characteristics providetosomeextentreasonableeconomicindicators. Bodysizeandshapeareimportanttraitsinmeatanimals. Thecharacterizationoflocalgeneticresourcesdepends on the knowledge of the variation of morphological traits,whichhaveplayedaveryfundamentalroleinclassificationoflivestockbasedonsizeandshape(Ferraet al.,2010;Aggaet al.,2010;Lenget al.,2010;Yakubuet al., 2010a and b). Based on body conformation, meat production can better be estimated than other production propertiesmakingbodymeasurementsimportantselectioncriteria(Beneet al.,2007). However, the biological relationships among the morphological traits may be different if these body measurementsaretreatedasbivariatesratherthanmul102 tivariates. Principal component analysis is a multivariate technique which could be used with success when morphological variables are interdependent. Principal components are a weighted linear combination of correlatedvariables,explainingamaximalamountofvariance of the variables (Truxillo, 2003). This aids in data reduction,andbreaksmulticollinearitywhichmaylead towronginferences.Manyresearhershaveusedtheindependentfactorscoresderivedfrommultivariatetechniqueofprincipalcomponentfactoranalysistoestimate body weight (Yakubu and Ayoade, 2009), functional traits(KaracaorenandKardamideen,2008),andasaselectioncriterionfortheimprovementofbodysize(Pinto et al.,2006).Thistechniquehasalsobeenusedtoreduce thenumberofindependentvariablesinthepredictionof genomic breeding values (Macciotta and Gaspa, 2009). InSub-SaharanAfrica,thereisdearthofinformationon theinterrelationshipsamongbodyweightandmorphometrictraitsofgoatsusingamultivariateapproach. This study was aimed at providing objective descriptionofbodyshapeofWADandRSgoatsinsouthernNigeriausingprincipalcomponents.Italsotestedthe hypothesisthattherelationshipsinvolvingbodyweight andmorphologicaltraitsmaybedifferentwhenorthogonalconformationtraitsderivedfromtheprincipalcomponentfactoranalysisareusedinsteadoftheinter-correlatedoriginalmorphologicalvariables.Theinformation obtained would be helpful to researchers and livestock producers with policies to assist conservation and sustainableutilizationofthelocalgoatgeneticresourcesby theproperuseofmorphologicaltraits. MATERIALS AND METHODS 2.1 LOCATIONOFSTUDYANDANIMALS Thestudywascarriedoutinfiverandomlyselected statesinsouthernNigeria;namelyOgun,Oyo,Bayelsa, DeltaandRiversStates,respectively.Thisregionliesbetween the derived guinea savannah and the dense rain forest,borderedbytheAtlanticOcean. Twohundredandsixtyfivematuregoatscomprising118WestAfricanDwarf(WAD)(83femalesand35 males) and 147 Red Sokoto (RS) (37 females and 112 males) goats were randomly sampled in towns and villages. The animals were up to 24 months old as determinedbydentitionasdescribedbyWilsonandDurkin (1984). The goats originated from different flocks and wererearedunderthetraditionalextensivesystem. 2.2 TRAITSMEASURED The following measurements were taken on each animal: Bodyweight(BWT): Thiswastakenusingahanging scale.TheanimalswereturnedontheirbackinaHessian bagandtheweighttakenasthedifferencebetweenthe finalcombinedweightandtheweightofthebag. Height at withers (HW): A flat platform was used uponwhichtheanimalwasplaced.Theheightatwitherswasmeasuredasthedistancefromthesurfaceofthe platformtothewithersusingameasuringstick. Necklength(NL): Thenecklengthwastakenasa measurefromthebaseoftheskulltothepointofconnectionwiththetrunkusingatape-rule. Bodylength(BL): Bodylengthwasmeasuredusing atape-rule,asthedistancefromtheoccipitalprotuberancetothebaseofthetail. Heart girth (HG): The heart girth was measured bytakingthemeasurementofthecircumferenceofthe chestwithatape-rule. 2.4 STATISTICALANALYSIS The morphological traits were subjected to analysis of variance to determine genotype and sex effects. Meanswereseparatedusingthetwo-tailed,two-sample t-test. Pearson's coefficients of correlation (r) among bodyweightandthefourmorphometrictraitswereestimated. From the correlation matrix, data were generated for the principal component (PC) factor analysis. The determinant of the correlation matrix was used to testformulticollinearityandsingularity.Anti-imagecorrelations, Kaiser-Meyer- Olkin measures of sampling adequacy and Bartlett's Test of Sphericity (to test the nullhypothesisthattheoriginalcorrelationmatrixisan identitymatrix)werecomputedtotestthevalidityofthe factor analysis of the data sets. The appropriateness of thefactoranalysiswasfurthertestedusingcommunalitiesandratioofcasestovariables.Principalcomponent analysisaccordingtoEverittet al.(2001)isamethodfor transformingvariablesinamultivariatedatasetintonew variables, which are uncorrelated with each other and accountfordecreasingproportionsofthetotalvariance oftheoriginalvariables.Thecomponentsthemselvesare merelyweightedlinearcombinationsoftheoriginalvariables. Cumulative proportion of variance criterion was employedindeterminingthenumberofprincipalcomponentstoextract.Reproducedandresidualcorrelations were used to test the validity of the number of factors extracted.Thevarimaxcriterionoftheorthogonalrotationmethodwasemployedintherotationofthefactor matrix to enhance the interpretability of the principal components. The stepwise multiple regression procedure was usedtoobtainmodelsforpredictingbodyweightfrom bodymeasurements(1)andfromprincipalcomponent factorscores(2): BW=a+BiXi+...+BkXk BW=a+BiPCi+...+BkPCk (1) (2) whereBWisthebodyweight,aistheregressionintercept,Biisthei-thpartialregressioncoefficientofthei-th linearbodymeasurement,Xi orthei-thprincipalcomponent(PC). The factor programme of SPSS (2001) statistical packagewasusedfortheprincipalcomponentanalysis. RESULTS AND DISCUSSION 3.1 BODYWEIGHTANDMORPHOLOGYTRAITS Descriptive statistics of body weight and morphometrictraitsofWADandRSgoatsarepresentedinTable 1. Average body weight was significantly (P < 0.05) higher in RS than in WAD goats. Overall body linear measurementsfortheRSwerealsohigher(P<0.05)for theRSgoatscomparedtotheirWADcounterparts.All morphometrictraitsestimatedinthisstudywerehigher inmalescomparedtofemaleanimals.Thehigherbody measuresofRSgoatsimplythattheyareheavier,taller andlongerbreedcomparedtoWAD.Dossaet al.(2007) reportedhigheraveragevaluesof56.57cmand79.23cm forHWandBLrespectivelyforBeningoatpopulations comparedto54.46cmand49.89cmrespectivelyinNigeriangoats.ThelargedifferencesinBLbetweenNigerian andBeningoatsmaybepartiallyexplainedbybothdifferentmethodologiesusedinmeasurementsandinherentgeneticandgene-by-environmentdifferences. Sexual dimorphism can be phenotypically expressedasdifferencesinskeletalsizeand/orbodymass. Thelargervaluesreportedfortheconformationtraitsof malescomparedtofemalesareinagreementwithearlier reportsongoats(Vargaset al.,2007),sheep(Yakubuand Akinyemi,2010)andcattle(PolakandFrynta,2010),respectively.Theinfluenceofsexonthebodyweightand morphometric traits in this study are likely connected withtheusualbetween-sexhormonalactionwhichleads to differential growth rates. Isaac et al. (2005) reported thatsexualdimorphisminbodysizeisclearlywidespread amongmanymammaliantaxa,withmale-biaseddimorphismbeingthemorecommon,butcertainlynottheexclusivepattern.However,Bacchiet al.,(2010)foundno Table 1: Descriptive statistics of the morphological traits of Nigerian goats based on genotype and sex Preglednica 1: Opisna statistika morfoloskih lastnosti nigerijskih koz ob upostevanju genotipa in spola Traits Lastnosti BW HW NL BL HG WAD Mean 15.37 b b RedSokoto SE 0.38 0.50 0.37 0.50 0.60 SD 4.14 5.47 3.99 5.40 6.47 Mean 18.99 61.04 a a Female Zenske SD 4.41 6.64 6.99 6.47 8.44 Mean 15.58 50.74 b b Male Moski SE 0.34 0.68 0.35 0.65 0.65 SD 3.76 7.42 3.80 7.11 7.13 Mean 18.86 58.89 56.05 a a SE 0.36 0.54 0.57 0.53 0.69 SE 0.40 0.70 0.60 0.67 0.71 SD 4.79 8.48 7.29 8.16 8.60 19.06b 24.15a 57.89 19.43b 47.32 23.91a 58.21b 65.95a 59.12b 65.31a BW­bodyweight/telesnamasa,WH­withersheight/visinavihra,NL­necklength/dolzinavratu,BL­bodylength/dolzinatrupa,HG­Heart girth/obsegprsi,SE­standarderror/standardnanapaka,SD­standarddeviation/standardniodklon a,b Meansinthesamerowbearingdifferentsuperscriptsaresignificantlydifferent(P<0.05)/Povprecjavvsakivrsti,oznacenazrazlicnimicrkami, seznacilnorazlikujejo(p<0,05). sexualdimorphisminthemorphometriccharactersconsideredinLama guanicoe guanicoeinArgentina.Yakubu (2009)reportedthatthemorphologicaltraitsofmaleand femalegoatsweresimilar,althoughthissubmissionwere forkidscomparedtodatareportedforrelativelymature animalsinthepresentstudy. 3.2 PHENOTYPICCORRELATIONS Pearson'scoefficientsofcorrelationamong thevariouslineartypetraitsforWADandRSgoatsareshownin Tables2and3,respectively.InWADgoats,thehighest correlationbetweenBWandlinearbodymeasurements was recorded for BW and HW in males (r = 0.97) and betweenBWandHGinfemales(r=0.91).InRSgoats, however, the highest correlation was between BW and chest circumference in both sexes (r = 0.94 and 0.91; Table 2: Phenotypic correlations among body weight and linear body measurements of WAD goats according to sex * Preglednica 2: Fenotipske korelacije med telesno maso in linearnimi meritvami pri WAD kozah glede na spol * Traits BW WH NL BL HG 0.97 0.82 0.95 0.95 0.88 0.98 0.93 0.91 0.80 0.90 BW WH 0.86 NL 0.76 0.80 BL 0.91 0.93 0.86 HG 0.91 0.81 0.72 0.84 Table 3: Phenotypic correlations among body weight and linear body measurements of RS goats according to sex * Preglednica 3: Fenotipske korelacije med telesno maso in linearnimi meritvami pri RS kozah glede na spol * Traits BW WH NL BL HG 0.85 0.90 0.83 0.91 0.79 0.85 0.84 0.76 0.81 0.86 BW WH 0.76 NL 0.66 0.71 BL 0.81 0.80 0.57 HG 0.94 0.80 0.67 0.83 BW­bodyweight/telesnamasa,WH­withersheight/visinavihra, NL­necklength/dolzinavratu,BL­bodylength/dolzinatrupa,HG ­Heartgirth/obsegprsi; * Significant at P < 0.01 for all correlation coefficients / Znacilno pri p<0,01zavsekorelacijskekoeficiente. Uppermatrix:Femalegoats/Zgornjamatrika:zenskezivali. Lowermatrix:Malegoats/Spodnjamatrika:moskezivali. BW­bodyweight/telesnamasa,WH­withersheight/visinavihra, NL­necklength/dolzinavratu,BL­bodylength/dolzinatrupa,HG ­Heartgirth/obsegprsi; * Significant at P < 0.01 for all correlation coefficients / Znacilno pri p<0,01zavsekorelacijskekoeficiente. Uppermatrix:Femalegoats/Zgornjamatrika:zenskezivali. Lowermatrix:Malegoats/Spodnjamatrika:moskezivali. P<0.01forbothfemaleandmaleanimals,respectively). TherelationshipbetweenBWandNLwaslowestinboth sexes of WAD goats (r = 0.76 and 0.82 in female and maleanimals,respectively).Whilethelowestcorrelation wasequallyreportedforBWandNLinfemaleRSgoats (r=0.66),thatbetweenBWandBLwasobservedtobe lowestintheirmalecounterparts(r=0.83).Thecorrelationcoefficientsamongbody measurementswerepositive and significant (P<0.01) in both sexes of the two goatbreeds.Thepresentestimatesarecomparabletothe range of values recorded for goats in earlier researches (Yakubu,2009;Sowandeet al., 2010).ThepositivecorrelationsbetweenBWandmorphologicaltraitsobtained inthepresentstudyindicatethatanincreaseinanyone bodymeasurementwouldresultinacorrespondingincreaseinlivebodyweight.ThestrongrelationshipexistingbetweenBWandbodymeasurementssuggeststhat eitherorthecombinationofthesemorphologicaltraits correlation, revealing the proportion of the variance in thebodymeasurementscausedbytheunderlyingfactor. This was found to be sufficiently high for all the morphometrictraitsinWAD(0.84and0.81forfemaleand maleanimals)andRS(0.81and0.86)goats,respectively. Theoverallsignificanceofthecorrelationmatricestested withBartlett'sTestofSphericityforthebodydimensions oftheWADgoats(chi-square=361.38versus217.75for 3.3 PRINCIPALCOMPONENTMATRIX femaleandmaleanimals;P<0.01)andforRSgoats(chisquare=105.78versus436.65;P<0.01)providedenough The determinants of the correlation matrix (0.011 versus0.001,and0.044versus0.018forfemaleandmale supportforthevalidityofthefactoranalysisofthedata WADandRSgoats,respectively)(Tables4and5)were set.Thecommunalities,whichrepresenttheproportion greater than 0.00001 (minimum requirement) while ofthevarianceintheoriginalvariablesthatisaccounted forbythefactorsolution,rangedfrom0.91­0.99inWAD anti ­ image correlations computed showed that partial correlations were low, indicating that true factors and 0.86­0.99 in RS goats, respectively. These further existedinthedataofbothsexesofthetwogoatbreeds. lendcredencetotheappropriatenessofthefactoranalyThiswassupportedbyKaiser-Meyer-Olkinmeasureof sis.Theratioofcasestovariables(24to1inWADand samplingadequacystudiedfromthediagonalofpartial 29to1inRSgoatsfarexceedingtheminimumof5to1 standard)wasalsometassamplesizerequirement,whileestimatesoftheresidual Table 4: Eigenvalues and share of total variance along with factor loadings and correlationmatrixwerelowenough. communalities of the body measurements of WAD goats based on sex After varimax rotation of the comPreglednica 4: Eigen vrednosti in delez celokupne variance s korelacijskimi koeficiponentmatrixinWADgoats,twofactors enti ter skupno varianco faktorjev za telesne mere pri obeh spolih WAD koz wereextractedforeachsex,andtheseacFemale Male countedfor94.15%(females)and97.65% Traits PC1 PC2 Communality PC1 PC2 Communality (males) of the total variance. The factor pattern coefficients were used to assess WH 0.66 0.68 0.91 0.77 0.62 0.98 the relative contributions of the various NL 0.91 0.37 0.96 0.45 0.88 0.99 body measurements in determining the BL 0.71 0.67 0.95 0.70 0.69 0.97 numerical value of the corresponding HG 0.37 0.90 0.96 0.89 0.43 0.98 factor (principal component). In female Eigenvalue 3.48 0.29 3.70 0.21 WAD goats, NL and BL were more associated with the first PC while the sec%Variance 87.00 7.15 92.46 5.19 ondPChaditsloadingsforHWandHG, WH­withersheight/visinavihra,NL­necklength/dolzinavratu,BL­bodylength/ respectively. In their male counterparts, dolzinatrupa,HG­Heartgirth/obsegprsi; PC­principalcomponent/glavnakomponenta PC1 had its loadings for HG, BL and HWwhilePC2wassolelyrelatedtoneck Table 5: Eigenvalues and share of total variance along with factor loadings and length. However, in RS goats, measurecommunalities of the body measurements of Red Sokoto goats based on sex ments most highly correlated with PC1 Preglednica 5: Eigen vrednosti in delez celokupne variance s korelacijskimi koeficiwere BL, HG and HW (this explained enti ter skupno varianco faktorjev za telesne mere pri obeh spolih RS koz 79.89% and 86.38% of the generalized variance of females and males, respecFemale Male tively), and could be termed "body size Traits PC1 PC2 Communality PC1 PC2 Communality factor".PC2wasprimarilydeterminedby WH 0.77 0.52 0.86 0.82 0.47 0.89 necklength,whichaccountedfor11.36% NL 0.34 0.93 0.99 0.45 0.89 0.99 (females)and6.46%(males)ofthevariBL 0.93 0.25 0.92 0.88 0.39 0.93 ation. The principal components obtainedinthepresentstudycouldbeused HG 0.84 0.42 0.88 0.77 0.55 0.90 alongside other economic parameters in Eigenvalue 3.20 0.45 3.46 0.26 evaluatinganimalsformanagementpur%Variance 79.89 11.36 86.38 6.46 poses.Similarfindingshaveearlierbeen WH­withersheight/visinavihra,NL­necklength/dolzinavratu,BL­bodylength/ reported(Sadeket al.,2006;Yakubuet al., dolzinatrupa,HG­Heartgirth/obsegprsi; 2009;Yakubuet al.,2011).PrincipalcomPC­principalcomponent/glavnakomponenta couldbeusedtoestimateliveweightingoatsfairlywell in the situation where weighbridges or scales are not available.Theassociationmayalsobeusefulasselection criterionsincepositivecorrelationsoftraitssuggestthat thetraitsmaybeunderthesamegeneticinfluences. ponentanalysishasalsobeenemployedindetermining sex-specificdifferencesinsizeandmorphologyofbones ofNorthAfricangazellespecies(Andreset al.,2008)and carcasstraitsofgoats(Bonvillaniet al.,2010). Table 6: Principal component factor scores coefficients for the estimation of body weights of breed 1 and breed 2 goats based on sex Preglednica 6: Regresijski koeficienti glavnih komponent za oceno telesne mase dveh pasem koz glede na spol WAD Female Traits PC1 PC2 WH NL BL HG 0.15 0.26 -0.75 0.24 0.14 1.13 Male PC1 PC2 0.44 -0.08 0.09 0.29 RedSokoto Female PC1 PC2 0.27 0.13 Male PC1 PC2 0.52 -0.23 1.46 0.05 0.79 -0.57 0.31 3.4 PRINCIPALCOMPONENTFACTORSCORES The principal component factor score coefficients offemaleandmaleWADandRSgoatsarepresentedin Table6.Thefactorscorecoefficientscouldbeusedininsteadoftheoriginalinterdependentmorphologicaltraits inpredictingthebodyweightofgoats. 3.5 ESTIMATIONOFBODYWEIGHTOFGOATS FROMINTERDEPENDENTBODYMEASUREMENTSANDTHEIRINDEPENDENTPRINCIPALCOMPONENTFACTORSCORES The interdependent original body measurements andtheirindependentprincipalcomponentscoreswere used to predict body weight of goats (Tables 7 and 8). The results of the stepwise multiple regression analysis revealedthatHGwasthesinglevariableofutmostimportanceinthepredictionofBWinbothbreeds,withthe exceptionofmaleWADgoats,whereHWaloneaccount- 1.11 -0.75 -0.93 1.37 -0.51 1.16 -0.81 0.66 -0.44 0.43 -0.10 1.15 -0.86 WH­withersheight/visinavihra,NL­necklength/dolzinavratu, BL­bodylength/dolzinatrupa,HG­Heartgirth/obsegprsi; Table 7: Stepwise multiple regression of body weight on original body measurements and on their principal components factor scores of WAD goats Preglednica 7: Postopna multipla regresija telesne mase na originalne telesne mere in na faktorske vrednosti glavnih component pri WAD kozah Model Female (i) 1 2 (ii) 1 2 Male (i) 1 2 (ii) 1 2 Originalbodymeasurementsaspredictors Heightatwithers Heightatwithers Heartgirth Orthogonaltraitsaspredictors PC2 PC2 PC1 16.81 16.81 4.00 4.00 2.48 0.46 0.16 0.16 70.00 96.40 -17.12 -19.57 0.68 0.44 0.24 0.03 0.07 0.06 94.20 96.00 Originalbodymeasurementsaspredictors Heartgirth Heartgirth Bodylength Orthogonaltraitsaspredictors PC1 PC1 PC2 14.77 14.77 2.93 2.93 1.89 0.25 0.14 0.14 63.00 89.00 -18.59 -20.96 0.58 0.32 0.39 0.03 0.04 0.05 83.00 90.00 Explanatoryvariables(predictors) Intercept Regression Coefficient SE R2 SE­standarderror/standardnanapaka,R2­coefficientofdetermination/determinacijskikoeficient,PC­principalcomponent/glavnakomponenta Table 8: Stepwise multiple regression of body weight on original body measurements and on their principal components factor scores of Red Sokoto goats Preglednica 8: Postopna multipla regresija telesne mase na originalne telesne mere in na faktorske vrednosti glavnih component pri RS kozah Model Female (i) 1 (ii) 1 2 Male (i) 1 2 (ii) 1 2 Originalbodymeasurementsaspredictors Heartgirth Heartgirth Necklength Orthogonaltraitsaspredictors PC2 PC2 PC1 19.50 19.50 3.23 3.23 3.00 0.32 0.14 0.14 49.00 91.00 -13.94 -6.94 0.50 0.29 0.29 0.02 0.03 0.03 83.00 91.10 Originalbodymeasurementsaspredictors Heartgirth Orthogonaltraitsaspredictors PC1 PC1 PC2 17.42 14.42 2.57 2.57 1.34 0.33 0.24 0.24 63.00 81.00 -6.58 0.39 0.02 89.00 Explanatoryvariables(predictors) Intercept Regression Coefficient SE R2 SE­standarderror/standardnanapaka,R2­coefficientofdetermination/determinacijskikoeficient,PC­principalcomponent/glavnakomponenta edfor94.20%ofthevariationinbodyweight.However, acombinationofHGandBL(females)andHWandHG (males) of WAD goats increased the proportion of the explained variance to 90.00% and 96.00%, respectively. Similarly,theaccuracyofthepredictionmodelwasimproved(91.10%)inmaleRSgoatswhenNLwasadded toHG. Thepossibilityofusingsimplebodymeasurements thatcanbecarriedoutinthefieldtopredictimportant economic traits have been demonstrated (Vargas et al., 2007;OzkayaandBozkurt,2009;Yakubu2010aandb). Badiet al.(2002)andLenget al.(2010)recommended theuseofheartgirthasthemostreliablevariabletopredictBWunderfieldconditions.TheimportanceofHG inweightestimationcouldbeasaresultofthefactthat muscle, some fat along with bone structure contribute toitsformation.However,theuseofinterdependentexplanatoryvariablesshouldbetreatedwithcautionsince multicollinearity has been shown to be associated with unstableestimatesofregressioncoefficients(Malau-Aduliet al.,2004),renderingtheestimationoftheuniqueeffectsofthepredictorsimpossible.Thisjustifiestheuseof principalcomponentfactorscoresforprediction.These factorsareorthogonaltoeachotherandaremorereliable inweightestimation.PC1andPC2togetheraccounted for89.00%and96.40%ofthevariationinbodyweight offemaleandmaleWADgoats,respectively.InRSgoats, a combination of PC1 and PC2 explained 81.00% (females)and91.00%(males)ofthetotalvariabilityinbody weight.Similarly,Keskinet al.(2007)andEyduranet al. (2009) used factor score coefficients to predict carcass andweaningweights,respectivelyinsmallruminants. CONCLUSIONS The principal component factor analysis led to an objectivesimultaneousanalysisofWH,NL,BLandHG of WAD and RS goats rather than on individual basis. This resulted in the reduction of the body dimensions to two PCs in each sex of the two goat breeds. The resultantfactorscorecoefficientscouldbeusedtopredict bodyweightwithmoreaccuracythantheoriginalinterdependentvariables.Thisisbecausemulticollinearityof twoormoreindependentbodymeasurementscouldlead tounstableregressioncoefficients,therebyleadingtoer roneous inferences. Results of the present investigation couldassistfarmersandgeneticimprovementspecialists whenconductingmanagement,selectionandpreservationprogramsinNigeriangoats. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Agriculturae Slovenica de Gruyter

Application of multivariate principal component analysis to morphological characterization of indigenous goats in Southern Nigeria

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10.2478/v10014-011-0026-4
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doi:10.2478/v10014-011-0026-4 COBISS:1.01 Agriscategorycode:L01 MosesOKPEKU1,2,#,AbdulmojeedYAKUBU3,#,SundayOlusolaPETERS2,4, MichaelOhiokhuaoboOZOJE2,ChristianObioraNdubuisiIKEOBI2, OlufunmilayoAyokaADEBAMBO2,IkhideGodwinIMUMORIN4,* ReceivedJuly22,2011;acceptedSeptember15,2011. Delojeprispelo22.julija2011,sprejeto15.septembra2011. Application of multivariate principal component analysis to morphological characterization of indigenous goats in South ern Nigeria Phenotypicvariationpresentinapopulationarisesdueto genotypicandenvironmentaleffects,andthemagnitudeofphenotypic variability differs under different environmental conditions, therefore, the purpose of this study was to objectively describethelineartypetraitsofextensivelymanagedmatureindigenousgoats ofSouthernNigeria andtopredict bodyweight from their orthogonal shape characters using principal componentanalysis.Bodyweightandfourbodymeasurements namely, height at withers, neck length, body length and heart girth were measured in 265 randomlyselectedWestAfricanDwarf(WAD) andRedSokoto(RS)goatsofbothsexes.RSgoatshadsignificantly(P<0.05)highermorphologicaltraitscomparedtotheirWAD counterparts. Sexual dimorphism was observed in all the traits with higher values recorded for males. Phenotypic correlations amongbodyweightandbiometrictraitswerepositiveandhighly significant(r=0.76­0.91versus0.82­0.97and0.66­0.94versus 0.83­0.91forWADandRSfemaleandmalegoats,respectively). Inthevarimaxrotatedprincipalcomponentfactoranalysis,two factors were extracted for each sex of the two breeds, although with varying degrees of factor loadings. The principal componentbasedregressionmodels,whicharepreferableforselecting animalsforoptimalbalance,accountedfor89.00and96.00%as well as 81.00 and 91.00% of the variation in body weight of femaleandmaleWADandRSgoats,respectively.Theinformation obtainedcouldbeusefulindesigningappropriatemanagement, selectionandbreedingprogrammesforutilizationofgoatgenetic resources. Key words: goats / autochthonous breeds / body traits / multivariateanalysis/Nigeria 1 2 3 4 # * Uporaba multivariatne analize glavnih komponent pri morfoloski karakterizaciji avtohtonih koz v juzni Nigeriji Fenotipska variabilnost v populaciji je pogojena z delovanjemgenetskihinokoljskihdejavnikov.Kerjeobsegfenotipske variabilnostirazlicenvrazlicnihokoljih,smoskusalivtejstudiji objektivno predstaviti linearne eksterierne lastnosti ekstenzivnovzrejanihavtohtonihkozvjuzniNigerijiinzanalizoglavnih komponentnapovedatitelesnomasonaosnovilastnosti,kiopredeljujejonjihovotelesnoobliko.Izmerilismotelesnomasoinstiri telesnemere(visinavvihru,dolzinavratu,dolzinatrupainobsegprsi)pri265nakljucnoizbranihzahodnoafriskihpritlikavih kozah(WestAfricanDwarf,WAD)inrdecihsokotokozah(Red Sokoto,RS)obehspolov.Vrednostizamerjenelastnostisobilepri RSkozahstatisticnoznacilno(p<0,05)vecjekotpriWADkozah. Spolni dimorfizem smo zabelezili pri vseh lastnostih, z vecjimi vrednostmizasamce.Fenotipskekorelacijemedtelesnomasoin biometricnimi lastnostmi so bile pozitivne in statisticno visoko znacilne(r=0,76­0,91in0,82­0.97ter0,66­0,94in0,83­0,91za WADinRSzivalizenskegatermoskegaspola).SfaktorskoanalizozVarimaxrotacijosmozavsakoodobehpaseminvsakspol dobilipodvafaktorja.Regresijskimodeli,kitemeljijonaanalizi glavnih komponent in so primerni za selekcijo zivali, so pojasnili89,00in96,00%,ter81,00in91,00%variancetelesneteze zenskihinmoskihzivalipasemWADinRS.Zbraneinformacije bodo uporabne pri upravljanju, selekciji in nacrtovanju rejskih programovzaboljseizkoriscanjegenskihvirovprikozah. Kljucne besede: koze / avtohtone pasme / telesne mere / multivariantnaanaliza/Nigerija NigerDeltaUniv.,Dept.ofLivestockProductionWilberforceIsland,P.M.B.071,Amassoma,BayelsaState,Nigeria Univ.ofAgriculture,Dept.ofAnimalBreedingandGenetics,Abeokuta,P.M.B.2240,Abeokuta,Nigeria NasarawaStateUniv.,Dept.ofAnimalScience,Fac.ofAgriculture,LafiaCampus,P.M.B.135,Lafia,Nigeria CornellUniv.,Dept.ofAnimalScience,267MorrisonHall,Ithaca,NY14853,USA Bothauthorscontributedequallytothispaper. Correspondence: Dr. Ikhide Godwin Imumorin, Dept. of Animal Science, Cornell Univ., Ithaca, NY 14853, USA, Tel: +1 607-255-2850, Fax: +1 607-255-9829, E-mail:igi2@cornell.edu Acta argiculturae Slovenica, 98/2, 101­109, Ljubljana 2011 INTRODUCTION Livestock of different species fulfill different functionsinthehouseholdeconomyandpoorfamiliesoften keep a diversity of species for this reason (Anderson, 2003). Domestic goats (Capra hircus, L.) are important andadaptabledomesticatedanimals(AbdelAziz,2010). Theyprovideafullrangeofusefulproductstohumans includingmeat,milk,skinandhair.Theyefficientlysurviveonavailableshrubsandtreesinadverseharshenvironmentandinlowfertilitylandswherenoothercrops canbegrowninNigeria.Goatproductionovertheyears isoneofthemajormeansofimprovingthelivelihoods ofpoorlivestockkeepers,reducingpovertyandattaining sustainableagricultureanduniversalfoodsecurity(AbdelAziz,2010).ThepopulationofgoatsinNigeriaisestimatedat53.8million(FAOSTAT,2011)ofwhichtraditionallyrearedstockcontributes99.97%,while0.03%of thestockiscommerciallymanaged.Basedonmorphology, the two most important goat breeds traditionally recognized in Nigeria are the Red Sokoto (RS) and the WestAfricanDwarf(WAD)goats,respectively(Ebozoje and Ikeobi, 1998). The WAD goat, which is trypanotolerant,isnativetothesouthernrainforestandderived savanahzoneswhiletheRSgoat,highlyreputedforits quality skin (found more in the northern axis) is more widelydistributedacrossthecountry. The diversity in gene pool and influence of varied climatic conditions have given rise to different local populations of goats which are repositories of unique genes that should be conserved for local and international future benefits (Adebambo, 2004). According to Groeneveldet al.(2010),identifyingandunderstanding auniquegeneticresourceinaparticularregionandthe development andproperuseof theassociateddiversity isaglobalresponsibility.Breedcharacterizationhasaccordingly been recognized as the first approach to the sustainableuseofanimalgeneticresource(Lanariet al., 2003). It is believed that various breed characteristics providetosomeextentreasonableeconomicindicators. Bodysizeandshapeareimportanttraitsinmeatanimals. Thecharacterizationoflocalgeneticresourcesdepends on the knowledge of the variation of morphological traits,whichhaveplayedaveryfundamentalroleinclassificationoflivestockbasedonsizeandshape(Ferraet al.,2010;Aggaet al.,2010;Lenget al.,2010;Yakubuet al., 2010a and b). Based on body conformation, meat production can better be estimated than other production propertiesmakingbodymeasurementsimportantselectioncriteria(Beneet al.,2007). However, the biological relationships among the morphological traits may be different if these body measurementsaretreatedasbivariatesratherthanmul102 tivariates. Principal component analysis is a multivariate technique which could be used with success when morphological variables are interdependent. Principal components are a weighted linear combination of correlatedvariables,explainingamaximalamountofvariance of the variables (Truxillo, 2003). This aids in data reduction,andbreaksmulticollinearitywhichmaylead towronginferences.Manyresearhershaveusedtheindependentfactorscoresderivedfrommultivariatetechniqueofprincipalcomponentfactoranalysistoestimate body weight (Yakubu and Ayoade, 2009), functional traits(KaracaorenandKardamideen,2008),andasaselectioncriterionfortheimprovementofbodysize(Pinto et al.,2006).Thistechniquehasalsobeenusedtoreduce thenumberofindependentvariablesinthepredictionof genomic breeding values (Macciotta and Gaspa, 2009). InSub-SaharanAfrica,thereisdearthofinformationon theinterrelationshipsamongbodyweightandmorphometrictraitsofgoatsusingamultivariateapproach. This study was aimed at providing objective descriptionofbodyshapeofWADandRSgoatsinsouthernNigeriausingprincipalcomponents.Italsotestedthe hypothesisthattherelationshipsinvolvingbodyweight andmorphologicaltraitsmaybedifferentwhenorthogonalconformationtraitsderivedfromtheprincipalcomponentfactoranalysisareusedinsteadoftheinter-correlatedoriginalmorphologicalvariables.Theinformation obtained would be helpful to researchers and livestock producers with policies to assist conservation and sustainableutilizationofthelocalgoatgeneticresourcesby theproperuseofmorphologicaltraits. MATERIALS AND METHODS 2.1 LOCATIONOFSTUDYANDANIMALS Thestudywascarriedoutinfiverandomlyselected statesinsouthernNigeria;namelyOgun,Oyo,Bayelsa, DeltaandRiversStates,respectively.Thisregionliesbetween the derived guinea savannah and the dense rain forest,borderedbytheAtlanticOcean. Twohundredandsixtyfivematuregoatscomprising118WestAfricanDwarf(WAD)(83femalesand35 males) and 147 Red Sokoto (RS) (37 females and 112 males) goats were randomly sampled in towns and villages. The animals were up to 24 months old as determinedbydentitionasdescribedbyWilsonandDurkin (1984). The goats originated from different flocks and wererearedunderthetraditionalextensivesystem. 2.2 TRAITSMEASURED The following measurements were taken on each animal: Bodyweight(BWT): Thiswastakenusingahanging scale.TheanimalswereturnedontheirbackinaHessian bagandtheweighttakenasthedifferencebetweenthe finalcombinedweightandtheweightofthebag. Height at withers (HW): A flat platform was used uponwhichtheanimalwasplaced.Theheightatwitherswasmeasuredasthedistancefromthesurfaceofthe platformtothewithersusingameasuringstick. Necklength(NL): Thenecklengthwastakenasa measurefromthebaseoftheskulltothepointofconnectionwiththetrunkusingatape-rule. Bodylength(BL): Bodylengthwasmeasuredusing atape-rule,asthedistancefromtheoccipitalprotuberancetothebaseofthetail. Heart girth (HG): The heart girth was measured bytakingthemeasurementofthecircumferenceofthe chestwithatape-rule. 2.4 STATISTICALANALYSIS The morphological traits were subjected to analysis of variance to determine genotype and sex effects. Meanswereseparatedusingthetwo-tailed,two-sample t-test. Pearson's coefficients of correlation (r) among bodyweightandthefourmorphometrictraitswereestimated. From the correlation matrix, data were generated for the principal component (PC) factor analysis. The determinant of the correlation matrix was used to testformulticollinearityandsingularity.Anti-imagecorrelations, Kaiser-Meyer- Olkin measures of sampling adequacy and Bartlett's Test of Sphericity (to test the nullhypothesisthattheoriginalcorrelationmatrixisan identitymatrix)werecomputedtotestthevalidityofthe factor analysis of the data sets. The appropriateness of thefactoranalysiswasfurthertestedusingcommunalitiesandratioofcasestovariables.Principalcomponent analysisaccordingtoEverittet al.(2001)isamethodfor transformingvariablesinamultivariatedatasetintonew variables, which are uncorrelated with each other and accountfordecreasingproportionsofthetotalvariance oftheoriginalvariables.Thecomponentsthemselvesare merelyweightedlinearcombinationsoftheoriginalvariables. Cumulative proportion of variance criterion was employedindeterminingthenumberofprincipalcomponentstoextract.Reproducedandresidualcorrelations were used to test the validity of the number of factors extracted.Thevarimaxcriterionoftheorthogonalrotationmethodwasemployedintherotationofthefactor matrix to enhance the interpretability of the principal components. The stepwise multiple regression procedure was usedtoobtainmodelsforpredictingbodyweightfrom bodymeasurements(1)andfromprincipalcomponent factorscores(2): BW=a+BiXi+...+BkXk BW=a+BiPCi+...+BkPCk (1) (2) whereBWisthebodyweight,aistheregressionintercept,Biisthei-thpartialregressioncoefficientofthei-th linearbodymeasurement,Xi orthei-thprincipalcomponent(PC). The factor programme of SPSS (2001) statistical packagewasusedfortheprincipalcomponentanalysis. RESULTS AND DISCUSSION 3.1 BODYWEIGHTANDMORPHOLOGYTRAITS Descriptive statistics of body weight and morphometrictraitsofWADandRSgoatsarepresentedinTable 1. Average body weight was significantly (P < 0.05) higher in RS than in WAD goats. Overall body linear measurementsfortheRSwerealsohigher(P<0.05)for theRSgoatscomparedtotheirWADcounterparts.All morphometrictraitsestimatedinthisstudywerehigher inmalescomparedtofemaleanimals.Thehigherbody measuresofRSgoatsimplythattheyareheavier,taller andlongerbreedcomparedtoWAD.Dossaet al.(2007) reportedhigheraveragevaluesof56.57cmand79.23cm forHWandBLrespectivelyforBeningoatpopulations comparedto54.46cmand49.89cmrespectivelyinNigeriangoats.ThelargedifferencesinBLbetweenNigerian andBeningoatsmaybepartiallyexplainedbybothdifferentmethodologiesusedinmeasurementsandinherentgeneticandgene-by-environmentdifferences. Sexual dimorphism can be phenotypically expressedasdifferencesinskeletalsizeand/orbodymass. Thelargervaluesreportedfortheconformationtraitsof malescomparedtofemalesareinagreementwithearlier reportsongoats(Vargaset al.,2007),sheep(Yakubuand Akinyemi,2010)andcattle(PolakandFrynta,2010),respectively.Theinfluenceofsexonthebodyweightand morphometric traits in this study are likely connected withtheusualbetween-sexhormonalactionwhichleads to differential growth rates. Isaac et al. (2005) reported thatsexualdimorphisminbodysizeisclearlywidespread amongmanymammaliantaxa,withmale-biaseddimorphismbeingthemorecommon,butcertainlynottheexclusivepattern.However,Bacchiet al.,(2010)foundno Table 1: Descriptive statistics of the morphological traits of Nigerian goats based on genotype and sex Preglednica 1: Opisna statistika morfoloskih lastnosti nigerijskih koz ob upostevanju genotipa in spola Traits Lastnosti BW HW NL BL HG WAD Mean 15.37 b b RedSokoto SE 0.38 0.50 0.37 0.50 0.60 SD 4.14 5.47 3.99 5.40 6.47 Mean 18.99 61.04 a a Female Zenske SD 4.41 6.64 6.99 6.47 8.44 Mean 15.58 50.74 b b Male Moski SE 0.34 0.68 0.35 0.65 0.65 SD 3.76 7.42 3.80 7.11 7.13 Mean 18.86 58.89 56.05 a a SE 0.36 0.54 0.57 0.53 0.69 SE 0.40 0.70 0.60 0.67 0.71 SD 4.79 8.48 7.29 8.16 8.60 19.06b 24.15a 57.89 19.43b 47.32 23.91a 58.21b 65.95a 59.12b 65.31a BW­bodyweight/telesnamasa,WH­withersheight/visinavihra,NL­necklength/dolzinavratu,BL­bodylength/dolzinatrupa,HG­Heart girth/obsegprsi,SE­standarderror/standardnanapaka,SD­standarddeviation/standardniodklon a,b Meansinthesamerowbearingdifferentsuperscriptsaresignificantlydifferent(P<0.05)/Povprecjavvsakivrsti,oznacenazrazlicnimicrkami, seznacilnorazlikujejo(p<0,05). sexualdimorphisminthemorphometriccharactersconsideredinLama guanicoe guanicoeinArgentina.Yakubu (2009)reportedthatthemorphologicaltraitsofmaleand femalegoatsweresimilar,althoughthissubmissionwere forkidscomparedtodatareportedforrelativelymature animalsinthepresentstudy. 3.2 PHENOTYPICCORRELATIONS Pearson'scoefficientsofcorrelationamong thevariouslineartypetraitsforWADandRSgoatsareshownin Tables2and3,respectively.InWADgoats,thehighest correlationbetweenBWandlinearbodymeasurements was recorded for BW and HW in males (r = 0.97) and betweenBWandHGinfemales(r=0.91).InRSgoats, however, the highest correlation was between BW and chest circumference in both sexes (r = 0.94 and 0.91; Table 2: Phenotypic correlations among body weight and linear body measurements of WAD goats according to sex * Preglednica 2: Fenotipske korelacije med telesno maso in linearnimi meritvami pri WAD kozah glede na spol * Traits BW WH NL BL HG 0.97 0.82 0.95 0.95 0.88 0.98 0.93 0.91 0.80 0.90 BW WH 0.86 NL 0.76 0.80 BL 0.91 0.93 0.86 HG 0.91 0.81 0.72 0.84 Table 3: Phenotypic correlations among body weight and linear body measurements of RS goats according to sex * Preglednica 3: Fenotipske korelacije med telesno maso in linearnimi meritvami pri RS kozah glede na spol * Traits BW WH NL BL HG 0.85 0.90 0.83 0.91 0.79 0.85 0.84 0.76 0.81 0.86 BW WH 0.76 NL 0.66 0.71 BL 0.81 0.80 0.57 HG 0.94 0.80 0.67 0.83 BW­bodyweight/telesnamasa,WH­withersheight/visinavihra, NL­necklength/dolzinavratu,BL­bodylength/dolzinatrupa,HG ­Heartgirth/obsegprsi; * Significant at P < 0.01 for all correlation coefficients / Znacilno pri p<0,01zavsekorelacijskekoeficiente. Uppermatrix:Femalegoats/Zgornjamatrika:zenskezivali. Lowermatrix:Malegoats/Spodnjamatrika:moskezivali. BW­bodyweight/telesnamasa,WH­withersheight/visinavihra, NL­necklength/dolzinavratu,BL­bodylength/dolzinatrupa,HG ­Heartgirth/obsegprsi; * Significant at P < 0.01 for all correlation coefficients / Znacilno pri p<0,01zavsekorelacijskekoeficiente. Uppermatrix:Femalegoats/Zgornjamatrika:zenskezivali. Lowermatrix:Malegoats/Spodnjamatrika:moskezivali. P<0.01forbothfemaleandmaleanimals,respectively). TherelationshipbetweenBWandNLwaslowestinboth sexes of WAD goats (r = 0.76 and 0.82 in female and maleanimals,respectively).Whilethelowestcorrelation wasequallyreportedforBWandNLinfemaleRSgoats (r=0.66),thatbetweenBWandBLwasobservedtobe lowestintheirmalecounterparts(r=0.83).Thecorrelationcoefficientsamongbody measurementswerepositive and significant (P<0.01) in both sexes of the two goatbreeds.Thepresentestimatesarecomparabletothe range of values recorded for goats in earlier researches (Yakubu,2009;Sowandeet al., 2010).ThepositivecorrelationsbetweenBWandmorphologicaltraitsobtained inthepresentstudyindicatethatanincreaseinanyone bodymeasurementwouldresultinacorrespondingincreaseinlivebodyweight.ThestrongrelationshipexistingbetweenBWandbodymeasurementssuggeststhat eitherorthecombinationofthesemorphologicaltraits correlation, revealing the proportion of the variance in thebodymeasurementscausedbytheunderlyingfactor. This was found to be sufficiently high for all the morphometrictraitsinWAD(0.84and0.81forfemaleand maleanimals)andRS(0.81and0.86)goats,respectively. Theoverallsignificanceofthecorrelationmatricestested withBartlett'sTestofSphericityforthebodydimensions oftheWADgoats(chi-square=361.38versus217.75for 3.3 PRINCIPALCOMPONENTMATRIX femaleandmaleanimals;P<0.01)andforRSgoats(chisquare=105.78versus436.65;P<0.01)providedenough The determinants of the correlation matrix (0.011 versus0.001,and0.044versus0.018forfemaleandmale supportforthevalidityofthefactoranalysisofthedata WADandRSgoats,respectively)(Tables4and5)were set.Thecommunalities,whichrepresenttheproportion greater than 0.00001 (minimum requirement) while ofthevarianceintheoriginalvariablesthatisaccounted forbythefactorsolution,rangedfrom0.91­0.99inWAD anti ­ image correlations computed showed that partial correlations were low, indicating that true factors and 0.86­0.99 in RS goats, respectively. These further existedinthedataofbothsexesofthetwogoatbreeds. lendcredencetotheappropriatenessofthefactoranalyThiswassupportedbyKaiser-Meyer-Olkinmeasureof sis.Theratioofcasestovariables(24to1inWADand samplingadequacystudiedfromthediagonalofpartial 29to1inRSgoatsfarexceedingtheminimumof5to1 standard)wasalsometassamplesizerequirement,whileestimatesoftheresidual Table 4: Eigenvalues and share of total variance along with factor loadings and correlationmatrixwerelowenough. communalities of the body measurements of WAD goats based on sex After varimax rotation of the comPreglednica 4: Eigen vrednosti in delez celokupne variance s korelacijskimi koeficiponentmatrixinWADgoats,twofactors enti ter skupno varianco faktorjev za telesne mere pri obeh spolih WAD koz wereextractedforeachsex,andtheseacFemale Male countedfor94.15%(females)and97.65% Traits PC1 PC2 Communality PC1 PC2 Communality (males) of the total variance. The factor pattern coefficients were used to assess WH 0.66 0.68 0.91 0.77 0.62 0.98 the relative contributions of the various NL 0.91 0.37 0.96 0.45 0.88 0.99 body measurements in determining the BL 0.71 0.67 0.95 0.70 0.69 0.97 numerical value of the corresponding HG 0.37 0.90 0.96 0.89 0.43 0.98 factor (principal component). In female Eigenvalue 3.48 0.29 3.70 0.21 WAD goats, NL and BL were more associated with the first PC while the sec%Variance 87.00 7.15 92.46 5.19 ondPChaditsloadingsforHWandHG, WH­withersheight/visinavihra,NL­necklength/dolzinavratu,BL­bodylength/ respectively. In their male counterparts, dolzinatrupa,HG­Heartgirth/obsegprsi; PC­principalcomponent/glavnakomponenta PC1 had its loadings for HG, BL and HWwhilePC2wassolelyrelatedtoneck Table 5: Eigenvalues and share of total variance along with factor loadings and length. However, in RS goats, measurecommunalities of the body measurements of Red Sokoto goats based on sex ments most highly correlated with PC1 Preglednica 5: Eigen vrednosti in delez celokupne variance s korelacijskimi koeficiwere BL, HG and HW (this explained enti ter skupno varianco faktorjev za telesne mere pri obeh spolih RS koz 79.89% and 86.38% of the generalized variance of females and males, respecFemale Male tively), and could be termed "body size Traits PC1 PC2 Communality PC1 PC2 Communality factor".PC2wasprimarilydeterminedby WH 0.77 0.52 0.86 0.82 0.47 0.89 necklength,whichaccountedfor11.36% NL 0.34 0.93 0.99 0.45 0.89 0.99 (females)and6.46%(males)ofthevariBL 0.93 0.25 0.92 0.88 0.39 0.93 ation. The principal components obtainedinthepresentstudycouldbeused HG 0.84 0.42 0.88 0.77 0.55 0.90 alongside other economic parameters in Eigenvalue 3.20 0.45 3.46 0.26 evaluatinganimalsformanagementpur%Variance 79.89 11.36 86.38 6.46 poses.Similarfindingshaveearlierbeen WH­withersheight/visinavihra,NL­necklength/dolzinavratu,BL­bodylength/ reported(Sadeket al.,2006;Yakubuet al., dolzinatrupa,HG­Heartgirth/obsegprsi; 2009;Yakubuet al.,2011).PrincipalcomPC­principalcomponent/glavnakomponenta couldbeusedtoestimateliveweightingoatsfairlywell in the situation where weighbridges or scales are not available.Theassociationmayalsobeusefulasselection criterionsincepositivecorrelationsoftraitssuggestthat thetraitsmaybeunderthesamegeneticinfluences. ponentanalysishasalsobeenemployedindetermining sex-specificdifferencesinsizeandmorphologyofbones ofNorthAfricangazellespecies(Andreset al.,2008)and carcasstraitsofgoats(Bonvillaniet al.,2010). Table 6: Principal component factor scores coefficients for the estimation of body weights of breed 1 and breed 2 goats based on sex Preglednica 6: Regresijski koeficienti glavnih komponent za oceno telesne mase dveh pasem koz glede na spol WAD Female Traits PC1 PC2 WH NL BL HG 0.15 0.26 -0.75 0.24 0.14 1.13 Male PC1 PC2 0.44 -0.08 0.09 0.29 RedSokoto Female PC1 PC2 0.27 0.13 Male PC1 PC2 0.52 -0.23 1.46 0.05 0.79 -0.57 0.31 3.4 PRINCIPALCOMPONENTFACTORSCORES The principal component factor score coefficients offemaleandmaleWADandRSgoatsarepresentedin Table6.Thefactorscorecoefficientscouldbeusedininsteadoftheoriginalinterdependentmorphologicaltraits inpredictingthebodyweightofgoats. 3.5 ESTIMATIONOFBODYWEIGHTOFGOATS FROMINTERDEPENDENTBODYMEASUREMENTSANDTHEIRINDEPENDENTPRINCIPALCOMPONENTFACTORSCORES The interdependent original body measurements andtheirindependentprincipalcomponentscoreswere used to predict body weight of goats (Tables 7 and 8). The results of the stepwise multiple regression analysis revealedthatHGwasthesinglevariableofutmostimportanceinthepredictionofBWinbothbreeds,withthe exceptionofmaleWADgoats,whereHWaloneaccount- 1.11 -0.75 -0.93 1.37 -0.51 1.16 -0.81 0.66 -0.44 0.43 -0.10 1.15 -0.86 WH­withersheight/visinavihra,NL­necklength/dolzinavratu, BL­bodylength/dolzinatrupa,HG­Heartgirth/obsegprsi; Table 7: Stepwise multiple regression of body weight on original body measurements and on their principal components factor scores of WAD goats Preglednica 7: Postopna multipla regresija telesne mase na originalne telesne mere in na faktorske vrednosti glavnih component pri WAD kozah Model Female (i) 1 2 (ii) 1 2 Male (i) 1 2 (ii) 1 2 Originalbodymeasurementsaspredictors Heightatwithers Heightatwithers Heartgirth Orthogonaltraitsaspredictors PC2 PC2 PC1 16.81 16.81 4.00 4.00 2.48 0.46 0.16 0.16 70.00 96.40 -17.12 -19.57 0.68 0.44 0.24 0.03 0.07 0.06 94.20 96.00 Originalbodymeasurementsaspredictors Heartgirth Heartgirth Bodylength Orthogonaltraitsaspredictors PC1 PC1 PC2 14.77 14.77 2.93 2.93 1.89 0.25 0.14 0.14 63.00 89.00 -18.59 -20.96 0.58 0.32 0.39 0.03 0.04 0.05 83.00 90.00 Explanatoryvariables(predictors) Intercept Regression Coefficient SE R2 SE­standarderror/standardnanapaka,R2­coefficientofdetermination/determinacijskikoeficient,PC­principalcomponent/glavnakomponenta Table 8: Stepwise multiple regression of body weight on original body measurements and on their principal components factor scores of Red Sokoto goats Preglednica 8: Postopna multipla regresija telesne mase na originalne telesne mere in na faktorske vrednosti glavnih component pri RS kozah Model Female (i) 1 (ii) 1 2 Male (i) 1 2 (ii) 1 2 Originalbodymeasurementsaspredictors Heartgirth Heartgirth Necklength Orthogonaltraitsaspredictors PC2 PC2 PC1 19.50 19.50 3.23 3.23 3.00 0.32 0.14 0.14 49.00 91.00 -13.94 -6.94 0.50 0.29 0.29 0.02 0.03 0.03 83.00 91.10 Originalbodymeasurementsaspredictors Heartgirth Orthogonaltraitsaspredictors PC1 PC1 PC2 17.42 14.42 2.57 2.57 1.34 0.33 0.24 0.24 63.00 81.00 -6.58 0.39 0.02 89.00 Explanatoryvariables(predictors) Intercept Regression Coefficient SE R2 SE­standarderror/standardnanapaka,R2­coefficientofdetermination/determinacijskikoeficient,PC­principalcomponent/glavnakomponenta edfor94.20%ofthevariationinbodyweight.However, acombinationofHGandBL(females)andHWandHG (males) of WAD goats increased the proportion of the explained variance to 90.00% and 96.00%, respectively. Similarly,theaccuracyofthepredictionmodelwasimproved(91.10%)inmaleRSgoatswhenNLwasadded toHG. Thepossibilityofusingsimplebodymeasurements thatcanbecarriedoutinthefieldtopredictimportant economic traits have been demonstrated (Vargas et al., 2007;OzkayaandBozkurt,2009;Yakubu2010aandb). Badiet al.(2002)andLenget al.(2010)recommended theuseofheartgirthasthemostreliablevariabletopredictBWunderfieldconditions.TheimportanceofHG inweightestimationcouldbeasaresultofthefactthat muscle, some fat along with bone structure contribute toitsformation.However,theuseofinterdependentexplanatoryvariablesshouldbetreatedwithcautionsince multicollinearity has been shown to be associated with unstableestimatesofregressioncoefficients(Malau-Aduliet al.,2004),renderingtheestimationoftheuniqueeffectsofthepredictorsimpossible.Thisjustifiestheuseof principalcomponentfactorscoresforprediction.These factorsareorthogonaltoeachotherandaremorereliable inweightestimation.PC1andPC2togetheraccounted for89.00%and96.40%ofthevariationinbodyweight offemaleandmaleWADgoats,respectively.InRSgoats, a combination of PC1 and PC2 explained 81.00% (females)and91.00%(males)ofthetotalvariabilityinbody weight.Similarly,Keskinet al.(2007)andEyduranet al. (2009) used factor score coefficients to predict carcass andweaningweights,respectivelyinsmallruminants. CONCLUSIONS The principal component factor analysis led to an objectivesimultaneousanalysisofWH,NL,BLandHG of WAD and RS goats rather than on individual basis. This resulted in the reduction of the body dimensions to two PCs in each sex of the two goat breeds. The resultantfactorscorecoefficientscouldbeusedtopredict bodyweightwithmoreaccuracythantheoriginalinterdependentvariables.Thisisbecausemulticollinearityof twoormoreindependentbodymeasurementscouldlead tounstableregressioncoefficients,therebyleadingtoer roneous inferences. Results of the present investigation couldassistfarmersandgeneticimprovementspecialists whenconductingmanagement,selectionandpreservationprogramsinNigeriangoats.

Journal

Acta Agriculturae Slovenicade Gruyter

Published: Dec 1, 2011

References