Age at first conception of high yielding cows

Abstract

Black and White low land dairy cattle have very pronounced ability for high production of milk. Fertility is the major trait of cattle and key factor in successful milk production. Fertility traits have pronounced variability and low heritability value. Fertility is regularly limiting factor in attempts to increase the milk yield. Age of dairy cattle at first conception is one of the major reproduction properties. Age of calves at first calving depends mainly on age at first conception. Previous researches have indicated what would be the optimum age at first conception of Black and White heifers. Age at first conception is determined by the date of birth and date of first conception. Knowledge of the strength of the environment factors on age at first conception in high yielding cows is important from the aspect of their inclusion into the model. According to the significance of individual systematic factors, their objective assessment was carried out for the purpose of accurate evaluation of obtained results. Objective of this paper is to study the age at first conception of high yielding Black and white cows through major systematic influences, by applying adequate methodology. Cows comprising the studied sample (n=331) belong to European type of Black and White dairy cattle in final stage of improving of this breed with Holstein-Friesian breed. Average age of dairy cattle at first conception was 491.19?9.36 days or 16.15?0.31 months. According to cows? the values were following: 479.31 days (> 73% HF), 486.12 days (58-73%HF) and 508.14 days (< 58% HF).Osobine plodnosti imaju izuzetno veliki ekonomski znacaj koji se ispoljava kroz normalan tok proizvodnog ciklusa. Jedna od njihovih vrlo vaznih specificnosti je veoma izrazena varijabilnost i niska naslednost. Uzrast grla kod prve oplodnje/teljenja je vazna osobina plodnosti goveda. Crno-bela nizijska goveda imaju izrazenu genetsku sposobnost za visoku proizvodnju mleka. Visokoproizvodne krave crno-bele rase izlozene su tokom produktivnog veka velikom broju slozenih uticaja. Uslovi proizvodnje vrlo cesto nisu u saglasnosti sa visokim potrebama ove rase. Problemi u reprodukciji cesto predstavljaju ogranicavajuci faktor za povecanje proizvodnje mleka. Unosenjem gena holstajn-frizijske rase u okviru programa oplemenjivanja evropskih crno-belih goveda doslo je do tendencije povecanja prinosa mleka i smanjenja plodnosti. Dosadasnja istrazivanja ukazuju na prihvatljiv uzrast pri prvoj oplodnji kod junica crno-bele rase. Poznavanje jacine uticaja sredine na uzrast pri prvoj oplodnji kod visokomlecnih krava vazno zbog njihovog ukljucivanja u model. U skladu sa pojedinacnim znacajem sistematskih faktora, obavljena je njihova objektivna procena radi sto tacnijeg vrednovanja ostvarenih rezultata. Cilj ovog rada je bio da se primenom odgovarajuce metodologije ispita uzrast kod prve oplodnje visokomlecnih crno-belih krava preko najvaznijih sistematskih uticaja. Krave u okviru ispitanog uzorka (n=331) pripadaju evropskim crno-belim nizijskim govedima u zavrsnoj fazi oplemenjivanja holstajn-frizijskom rasom. Prosecna starost grla pri prvoj oplodnji iznosila je 491.19?9.36 dana ili 16.15?0.31 meseci. Posmatrano po genotipovima krava iznosio je 479.31 dana (> 73%HF), 486.12 dana (58-73%HF) i 508.14 dana (< 58%HF). Na utvrdjene razlike u pogledu uzrasta pri prvoj oplodnji znacajan uticaj (p?0.05) pokazali su bikoviocevi, klasa HF gena krava nije imala znacajan uticaj (p>0.05), godina teljenja pokazala je visoko znacajan uticaj (p?0.01), dok je sezona teljenja ispoljila znacajan uticaj (p?0.05). PR Projekat Ministarstva nauke Republike Srbije, br. TR-31053