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In recent decades, there has been a downward trend in length of productivelife (LPL) in Holstein cows across industrial dairy herds. This studyexamined the factors that might influence LPL and estimated the geneticparameters of LPL in Holstein dairy herds in Isfahan province, Iran. LPL isdefined as the number of days between the first calving and the end ofrecording. Data consisted of 35 137 records of productive life fromregistered cows that started first calving between 1991 and 2012. Cows thatremained alive at the end of the study were considered right-censored. Theaverage lifetime for culled and censored cows was 938 and 1003 days,respectively. A survival analysis was applied using a proportional risk modelwith a Weibull distribution. Milk production was divided into five groups,where the culling risk of cows with a milk yield of less than 1.5 standarddeviations (SD) of the mean was 3.5 times greater than the culling risk ofhigh-producing cows producing more than 1.5 SD above the mean. Resultsshowed that culling risk increased almost linearly beyond the milk productiongroups. Furthermore, somatic cell count and age at first calvingsignificantly increased the culling risk across the herds. The results forthe combined effect of parity  ×  stage of lactation showed a decreasein culling risk during the first calving, and an increase during the furtherparities. Moreover, a higher age at first calving was observed, reflecting alower risk of culling. Estimated heritability were 0.074 and 0.18 based on alogarithmic scale and original scale, respectively. According to the results,use of Weibull models showed that the proportional culling risk was higher inlow-production cows, but a higher risk ratio was revealed inhigh-milk-production cows. However, there were some fluctuations in genetictrends, but an overall increase was observed in LPL which will lead to alonger LPL of Holstein cows in Isfahan province

Genetic analysis of productive life length in Holstein dairy cows using Weibull proportional risk model