Productive performance of F1 compared with other 50% European-zebu crossbred cows for dual purpose systems in the Venezuelan tropics

摘要

TheperformanceofHolstein-zebu(F1H)andBrownSwiss-zebucowsF1(F1BS)wascomparedwiththatofmixedinterse(MIS)crossbredsof50%European-zebuinheritance,using5054recordsfrom10dualpurposefarmsinVenezuela.TheF1Hcowsweremainlyprogenyof41USAHolsteinbullsofpositivegeneticvalueformilkyield,whilemostBSbullswereofunknownoraveragegeneticmerit.TheMIScowswereprogenyofcrossbredbullsofvariousgenotypes,generallyunselectedforperformancetraits.Recordsincludedlactationand244-daymilkyield,daysinmilk,daysopen,calfweightat4monthsandcalfmortalityfrombirthto4months.Datawereanalysedusinglinearmodelswhichincludedtheeffectsofbreedgroup(3),farm(10),calvingyear(1989...1997),calvingseason(wet,dry),calvingnumber(1..6+),andthefirstorderinteractionsinvolvingbreedgroup.Overalladjustedmeanvalues(±SE)were1637±35kgtotallactationyield,1436±27kg244-dayyield,246±5daysinmilk,139±5daysopen,60±0.7kgcalfweightat4monthsand8.6±1.6%calfmortality.Theonlysignificantbreedgroupeffectswerefoundformilkyield(P0.01)anddaysinmilk(P0.05),butthebreedgroupxfarminteractionwashighlysignificantforthesetraitsanddaysopen.TheHF1rankedfirstformilkyieldonnineofthetenfarms.Overall,theyexceededtheMISandF1BScowsby19%and14%,respectively,fortotalmilkyieldandby10%and13%fordaysinmilk,andshowednodisadvantageforanytrait.TherewerenosignificantdifferencesinperformancebetweentheF1BSandtheMIScows.Coefficientsofvariationwerecloselysimilarforallgroups.ItwasconcludedthatF1cowsmayofferanimportantadvantageovercommercial-typeintersecrosses.The19%increaseinmilkyieldperlactationoftheF1Hcowsmaywellcompensatethepracticaldisadvantagesofthematingsystemrequiredtoproducethem.However,theF1BSresultsshowedthattheadvantageoftheF1'sdoesnotalwaysoccurandmaydependontheEuropeanbreedused,and/orthequalityofthesireswithinthebreed.TheuseofMIScowsoffersimportantpracticaladvantages,especiallyforsmallfarms,andtheirperformanceshouldbeimproveablethroughmoresystematicselection.Therewasnoevidencethattheperformanceoftheprogenyofcrossbredbullsisunusuallyvariablefortraitsofimportanceindualpurposesystems.