Effect of milk yield-based selection on some reproductive traits of Holstein Friesian cows on large-scale dairy farms in Malawi

摘要

Thispaperdescribesastudyaimedatevaluatingtheeffectofselectingsiresbasedontheirbreedingvaluesformilkyieldestimatedintheircountriesoforiginonreproductiveperformanceoftheirdaughtersonlarge-scaledairyfarmsinMalawi.Todothisananalysiswasdoneusing2362recordsofpurebredHolsteinFriesiancattlekeptinCentralandSouthernMalawifrom1986to1996.Fixedeffectsofsiregroup,herd,yearandseasonofcalvingweretestedandrandomeffectsofdamandcowwereincludedinthestatisticalmodelapplied.(Co)variancecomponentswereestimatedthroughtherestrictedmaximumlikelihood(REML)procedure.Meannumberofservicesperconception(NSC)was1.50,gestationinterval(GI)was277days,calvingintervalbetweenfirstandsecondparity(CI1)was416days,calvingintervalbetweensecondandthirdparitytwoandthree(CI2)was408days,andageatfirstcalving(AFC)was32.5months.Ingeneralthemajorityofthereproductivetraitswereaffectedbythenon-geneticfactorsofherd,yearandseason.Siregroup,aproxyofthebreedingstrategy,hadasignificanteffectonAFC(p0.01)andCI2(p0.05).Factorsthathadsignificanteffects(p0.01)onmostofthereproductivetraitsinthestudywereherd,yearofinsemination,yearofcalving,andseasonofinsemination.PhenotypiccorrelationbetweenNSCandAFCwas0.19,betweenNSCandGIwas-0.05,whilethatbetweenNSCandCI2was0.14.HeritabilityestimatesforNSC,GI,CI1,andAFCwere,0.04,0.10,0.001,and0.20,respectively.Thehighvariationduetonon-geneticfactorsandthelowheritabilityestimatesforthereproductivetraitsindicatethatmuchimprovementcouldbemadethroughimprovedmanagement,husbandrypractices,andstrategicallyutilizingenvironmentalfactors.