LAUSR

The effect of age at first calving (AFC) and various non-genetic factors i.e. season of calving, farm and system of housing on longevity and production traits were investigated. Longevity traits were studied using total lifetime (TL), length of productive life (LPL) and number of lactations (NL) while production was researched using lifetime milk yield (LMY). Data of 2037 Holstein dairy cows were provided by the main breeding organizations at the Faculty of Agriculture, University of Novi Sad. The average values and variability of examined traits as well as the effect of factors on longevity and production traits were investigated using fixed effect model by general linear model (GLM) procedure in software package Statistica 13. Results showed highly significant effect of the AFC, calving season and farm, on all studied longevity traits (P less than 0.01), while non- significant effect was expressed on lifetime milk yield (P greater than 0.05). The mean of AFC, TL, LPL, NL and LMY for Holstein cows were 27.3, 67.5, 40.2 months, 2.45 and 18798.0 kg, respectively. The maximum values of LPL, NL and LMY were noticed for cows with age at first calving before 23 months of age. The LPL ranged from 47.88 (AFC less than 23 m) to 35.84 m (AFC>29 m) and declined progressively when the AFC is increased, particularly in cows calving at more than 29 m.