The aim of the study was to analyze the relationship between first lactation milk yield
(FLMY) and age at first calving (AFC), longevity and productive life in dairy cows. The study
covered 944 Holstein cows housed in 5 dairy cattle farms in Bulgaria. All cows from the five
farms culled in the period 2012–2018 with FLMY data were included. The average AFC for all
culled cows included in the study was relatively high for the Holstein-Friesian breed - 29.75
months. The average FLMY of the herds included in the study was 7,660.94 kg with significant
herd variation from 5,899.09 kg to 8,646.0 kg. Significant effect of the herd (P < 0.001), AFC
and the associated effect of the herd and AFC (P < 0.05) on the average FLMY were found. The
highest FLMY was reported in primiparous with AFC of 28–30 months – 7,860.8 kg, and the
lowest in those with AFC ≤ 24 months – 7322.8 kg. In the herd with the lowest average FLMY -
5,899.09 kg 27.5% of the heifers had calved at age over 34 months. A statistically significant
effect of AFC (P < 0.001) was found on longevity, whereas the productive life was significantly
influenced by FLMY (P < 0.05). A tendency for higher longevity for cows with higher AFC of
34–37 months and over 37 months – 5.9 and 5.8 years, respectively was observed. The lowest
were the longevity values for cows calved at age up to 24 months – 4.9 years. The cows with the
lowest average FLMY (up to 4,000 kg) had the shortest productive. Both very low and high AFC
were associated with lower first lactation cow productivity and shorter productive life. The losses
for farmers were greater when keeping a high AFC in heifers, which increases the cost for housing
them, and the lower productivity and longer productive life reduce the probability