بررسی عوامل موثر بر حذف در گاوهای شیری هلشتاین شمال غرب ایران

In this study the causes of culling in 9 industrial dairy farms in northwest of Iran between 2008 to 2013 were investigated. The impact of various factors on culling was analyzed using the GLIMIX procedure of SAS 9.2. The results showed that from 5404 dairy cows culled, voluntary and involuntary culling rate were 24.8% and 75.2 % respectively. Infertility and metabolic disorders were the most frequent causes of culling with 17.7%, and 16.8% respectively. The voluntary culling of female calves and heifers (before calving) was extremely high (60.55%) and for the heifers after calving was extremely low (5.06%). Almost 25.49% of culling occurred during the first 50 days after calving which was mostly involuntarily. The effect of independent variables including calving type (abortion, stillbirth, natural calving), dystocia, open days, lactation number, length of dry period and calving season on culling rate were all significant (pr<0.05). The cow with easy calving, low open days and moderate dry period (41-70 days) had the least culling rates. The results showed that the high frequency of involuntary culling of cattle led to the reduced longevity, selection intensity and increased the costs for dairy cattle industry.