PIRMĀS ATNEŠANĀS VECUMA IETEKME UZ HOLŠTEINAS ŠĶIRŅU GOVJU MŪŽA ILGUMU UN PIENA PRODUKTIVITĀTI.

First calving age is one of main factors affecting longevity and productivity of dairy cattle. Holstein black and white and Holstein red and white cows are characterizing with larger milk yields and with shorter lifespan than Latvian native cow breed. The aim of this study was to determine how age at first calving affects Holstein cow breed longevity and lifetime productivity. In study was used data of 45 973 Holstein black and white (31 184) and Holstein red and white(14 753) dairy cows that was culled from herds during the period from year 2002 to 2012. Data about dairy cow milk productivity, first calving used in study was obtained in Agricultural Data Centre. There was discovered that average lifespan of Holstein cow breed in Latvia is 1995.7 days with 22457.5 kg energy corrected milk (ECM) lifetime milk yield. Holstein black and white cow lifespan was 524 days or 1.36 years shorter than Holstein red and white cow, therefore Holstain black and white cows had largest productivity in one life day - 17.9 kg ECM - and in all life - 24735.9 kg ECM. Signifficantly longer (p<0.05) lifespan in both of Holstein breed cows was in cow group with first calving age <24, but lifetime milk productivity for Holstein red and white cows was in first calving age 24-29 months. Highest milk productivity was in Holstein black and white cow breed with first calving age <24 month, average lifetime milk productivity in this group was 25287.3 kg ECM. [ABSTRACT FROM AUTHOR]