Effect of age at first calving on lactation and reproduction of dairy cows reared in semi arid region of Algeria

摘要

ThisstudyinvestigatedeffectsofageatfirstcalvingonmilkyieldandreproductiveperformanceamongMontbéliardeheifersduringsixfirstlactationson4dairyfarmsinAlgeriansemiaridregion.Dataforreproductionof492cowsandlactationof352cowswereused.Heiferswereclassifiedaccordingtoageatfirstcalvingasearly(24to30months),medium(31to36months),andlate(37to42months).Effectsofherd,seasonofcalving,parityandageatfirstcalvingwereevaluated.nbsp;Averageageatfirstparturitionwas33.1months.Averagemilkproductionduringsecondandthirdlactationswas20to24%lowerthaninotherparitiesandcowscalvinginsummerproduced23and24%lowermilkperlactationthandidcowscalvingrespectivelyinwinterandspring.Milkyieldwassimilarbetweenallagegroupsatfirstandthirdlactations;howeverearlycalvinggroupproduced20and24%lessmilkyieldduringsecondlactationcomparedrespectivelytomediumandlatecalvinggroups,yielded1162and1037kglesscumulativemilkyieldforthreefirstlactations,and11and11.5%reducedcumulative305-daysmilkyieldforsixfirstlactations.Earlycalvinggrouprecordedsignificantlydelayedintervalbetweencalvingandconceptionandcalvinginterval(20to22days)atfirstparityandhadcomparableperformancestooldercalvingclassesduringpreviousparities.Dissimilarityofbodyweightandenergybalanceacrossgroupsofagewasprobablythemajorfactorsthatinfluencedreproductiveandmilkyieldefficiencyofcows.Optimumageatfirstcalvingforthisstudywas30to36months.