J. Bahrampour - Department of Animal Science, College of Agriculture, Ferdowsi University of Mashhad, P.O. Box: ۹۱۷۷۵–۱۱۶۳, Mashhad, Iran.
M. Danesh Mesgaran - Department of Animal Science, College of Agriculture, Ferdowsi University of Mashhad, P.O. Box: ۹۱۷۷۵–۱۱۶۳, Mashhad, Iran.
A. R. Arabpour - Department of Statistics, Faculty of Mathematics and Computer, Shahid Bahonar University of Kerman, Kerman, Iran.
A. Vakili - Department of Animal Science, College of Agriculture, Ferdowsi University of Mashhad, P.O. Box: ۹۱۷۷۵–۱۱۶۳, Mashhad, Iran.

This experiment was conducted to evaluate the association between risk factors and the risk of culling in Iranian Holstein cows. The data consisted of 329,772 lactation records obtained from the Animal Breeding Center of Iran (2003 - 2012) and logistic regression was applied to investigate the associations between the predictor and response variables. The response variable in this experiment was the risk of culling and predictor variables were included calving season, parity, birth type, calving ease, standardized 305-d milk yield, age at the first calving, region and the number of calving cows in the herd. Risk factors analysis showed that the risk of culling significantly (P< 0.001) increased with parity and twinning. The odds ratio of cows leaving the herd were 1.32, 1.55, 1.62, 1.67 and 1.88 for parities 2 to 6, respectively and 1.09 for twinnings. Also, the OR increased with increasing in calving difficulty score except for farmer assistant cow. The OR were 1.12, 1.36 and 1.23 for herds with 26 to 53, 54 to 125 and ≥126 calving cows and risk of culling was increased with increase in number of calving cows in the herd. Calving in hot season increased the risk of culling and cows calved in cool seasons had lower risk of culling. The OR were 0.87, 0.79 and .077 for summer, fall and winter respectively. The analysis showed that region had a significant effect (P< 0.001) on culling risk and cows in warm and dry and warm and semi-arid regions had a higher risk of culling compared the cows in temperate or cold and wet region. Risk of culling significantly (P< 0.001) decreased with increasing in standardized 305-d milk yield so that cows with higher milk yield had the lower risk of culling. Cows at the age first calving about 24 months had the lower risk of culling and with increasing the age at first calving, the risk of culling increased. In general, the obtained results showed that the evaluated risk factors can significantly affected the risk of culling in dairy farms and farmers can control and manage dairy cattle according to these factors.

Risk factors, Holstein cows, culling, Iran