High rate of culling in dairy-cow herds increase the costs of replacement heifers which is in contrast to developing of the herds. This study was performed to evaluate the important reasons for culling of dairy cattle in the first-lactation and estimate the genetic correlations between longevity and other traits. The records on 64,621 cows sired by 8,371 bulls, and born between 1989 and 2013 were collected from 52 Holstein dairy herds. Culling during the first lactation was scored as 1 for the cows with the second calving and also for the cows culled after 365-d from the first calving, and otherwise the cows scored as zero. A Bayesian multivariate threshold linear animal model using Gi sampling was used for statistical analysis. The models included both fixed effects (herd-year of calving, calving situation, milk yield and average of somatic cell score), and random effects (genetic effect of animal and residual). Longevity rates were 75.8% for the first lactation cows. The highest frequency caused to involuntary culling the cows was the reproductive failure with 27.5%. The frequencies of other causes were included: infectious diseases (13.2%), mastitis (10.1%), metabolic disorders (10.7%), and feet and legs problems (7.4%). Only 16.6% culled cows were due to voluntary culling. The estimated heritability was low (0.039± 0.0056) for linear animal model. Heritability estimates by threshold models were 2 times greater than linear model (0.081± 0.015). The posterior means of the genetic correlations between longevity and the other traits were 0.44 to 305-d milk yield, - 0.455 to lactation mean SCS, 0.30 to 305-d fat, 0.44 to days open and ?0.65 to interval from calving to first insemination. According to our results, productive life was increased genetically over the time by genetic selection for milk production. In contrast, its phenotypic mean decreased over the time due to environmental changes such as management and nutrition. Keywords: culling reasons, longevity, genetic parameter, trend, Holstein dairy cows.
