Environmental factors affecting the shape components of the lactation curves in Holstein dairy cattle of Iran

摘要

Theobjectivesofthisstudyweretoanalyzetheeffectsofsomeenvironmentalfactorsonlactationcurvetraits.Atotalof65757lactationsfrom40672cowscollectedfrom1999to2002bytheIraniananimalbreedingcenterwereused.Inordertoestimatelactationcurveparameters,incompletegammafunctionwhichwasproposedbywoodwasused.Lactationcurvetraitswhichwereanalyzedincludedascalingfactorassociatedwithlogarithmyieldatthebeginning,theinclininganddecliningslopesbeforeandafterpeakyield,DIMtoreachpeakyield,peakyield,persistencyand305-dmilkyield.nbsp;Theresultsshowedthatthelog-transformedofincompletegammafunctionexplained70.8%ofvariationindailymilkyield.Environmentalfactorssuchascalvingage,interactionofherd-yearofcalving,seasonofcalving,parityanddaysopenhadsignificanteffectsonlactationcurvetraits.ThehighestpersistencyandDIMuntilpeakyieldbutthelowestpeakyieldand305-dmilkyieldwerefor1stparitycows.Peakyieldhappenedlaterandwaslowerinthosecowscalvinginspring,comparedwiththosecalvinginotherseasonsaswellas305-dmilkyieldandpersistency.ThehighestcorrelationwasbetweenpersistencyandDIMuntilpeakyield(r=0.86)andthelowestcorrelationwasbetweenlogarithmyieldatthebeginningoflactationandfactorassociatedwiththeincliningslopeofthelactationcurves.305-dmilkyieldwashighlycorrelatedwithpeakyield(r=0.80)butcorrelationbetween305-dmilkyieldandpersistencywasrelativelylowandmostlypositive(r=0.055).