Considering the culling reasons and trend of its changes Using 16 years data of mega dairy Holstein farms in Iran

Cow culling is one of the main economic aspects in mega-dairy cattle farms management. Therefore, in this research the cow culling reasons in 20 Iranian industrial Holstein mega-dairy farms during the last 16 years (2005 -2021 years) was considered. A total of 129454 cows data were used to analyze by T-Student methods of SAS software version 9.4. Based on the culling reason, data were classified into 11 classes. The annual culling rate of the milking cows was approximately 23.5%. Predominant reasons for culling were fertility problems and abortion (23.7%), metabolic and digestive disorders (15.8%), and infectious disorders (15.6%). The investigation of the trend of culled cows showed that fertility problems and abortion increased from 22.0% in 2005 to 24.6% in 2021. Also, culled cow’s percentage for metabolic and digestive disorders decreased (from 24.0% to 13.0%) and the culling percentage in year 2021 significantly differed from the average of the past 15 years, also feet/claw disorders (P<0.01) and Infection diseases (P<0.01) were significantly higher than the average of the past 15 years. It means that in the final year of the report, the culling of cows due to metabolic and digestive problems as well as udder disorders decreased compared to the 16-year averages, voluntary culling did not increase or change, but the culling percentage due to infectious diseases and lameness was increased. Increasing trend of voluntary culling can be improved by improving fertility and preventing abortion, along with decreasing slaughter culling of lameness and infectious diseases, and ultimately increase herd profitability.