Testicular growth of Nelore bulls

摘要

Theaimofthisstudywastoevaluatethecorrelationofageandscrotalcircumference(SC)establishingtesticulargrowthcurveofNellorebulls.TheexperimentwascarriedoutintheJaítaFarm,Macarani-BA,fromJanuaryof2004toJanuaryof2006.Thereweremade1139measuresof778malesfrom5to70monthsofage.Theanimalsweregroupedintosevenclassesofage:age1(#8805;5to#8804;7months),age2(7to#8804;12months),age3(12to#8804;18months),age4(18to#8804;24months),age5(24to#8804;36months),age6(36to#8804;48months)andage7(48to#8804;70months).ThemodelusedtocharacterizethegrowthoftheSCinfunctionofagewasthelogisticmodel,SC=A/(1+B*exp#8211;Kt),whereSCisthescrotalcircumferenceattdaysofage,Aisscrotalcircumferenceatmaturity,BistheconstantintegrationestablishedbytheinitialvaluesofSCandt,whichadjuststhesituationwhenSC#8800;0and/ort#8800;0,Kismaturityconstant,whichequalstheratiobetweenthemaximumrateofgrowthandSCatmaturity.Forthelogisticfunction,estimatedSCatmaturity(A)was40.0cmat70monthsofageandinflectionpoint(timeofmaximumgrowth)wasreachedat11.32monthsofageataverageSCof20.0cm.HighandpositivecorrelationsbetweenSCandageallowthatselectionofNelloremalescanbeindicatedtothe12and18months,withSCofapproximately20,15cmand25.41cmrespectively.