Heat stress impact on the performances of lactating Holstein cows in central Tunisia

摘要

TheobjectivesofthepresentworkweretocharacterizetheintensityofheatstresstowhichdairycowsareexposedincentralTunisiausingtheTemperatureHumidityIndex(THI)andtostudythestresseffectsoncowperformancesusingElAlemdairyherdlocatedinKairoun,centralTunisia.First,todefinetheperiodofheatstressandthestressintensity,THIvalueswerecalculatedusinga10-yearperiod(2000-2009)averagemonthlytemperatureandrelativehumiditydatafromtheregionalweatherstationofElAlem.Then,averagemilkproductionpercow,majorreproductiveparametersaswellasthepercentagesofmastitisandabortionwerecalculatedusingavailableherddata.ResultsrevealedtheexistenceofasummerheatstressincentralTunisiafor4monthsgoingfromJunetoSeptemberwithTHIvaluesbeinggreaterthanTHIthreshholdof72,withTHIvaluesrangingbetween74±0.83and79±0.8.Milkpercowdroppedfrom19.6inMarchto15kgperdayinSeptember,whichisanaveragedecreaseofabout28%.Reproductiveparametersandthepercentagesofmastitisandabortionoccurrenceswerenegativelyaffectedbyheatstress.Theoverallconceptionrate(CR)waslowestinthesummer(25%forthemonthofJuneVs43.5%forNovember).AveragecalvingintervalswerelongestforcowscalvingduringMay-June(500daysforcowscalvinginmayvs.410daysforthosecalvinginNovember).ThehighestabortionratewasobservedfortheperiodgoingfromMaytoJulyandthatofmastitiswasforJune-September.Theresultsstresstheneedfortheimplementationofappropriateadaptationstrategiesthatcanbeusedbyfarmerstoreducethestressnegativeeffectsoncows.nbsp;Intheshortrun,theseshouldinvolvetheuseofimprovedfeedingandnutritionalmanagementpractices,appropriatereproductivemanagementplansandofsuitableenvironmentalcontroltechniques.Inthelongrun,geneticimprovementprogramssuchastheuseofcrossbreedingbetweenimportedHolsteincowsandthelocalbreedanimalsshouldbeimplemented,particularlyinareaswithseverstress,nbsp;toenhanceheattoleranceincrossbredcows.