Estimate the genetic parameters and analysis of culling reasons in Iranian Holstein dairy cattle

Many animals are culled from the herd on dairy farms annually due to health problems, and this involuntary culling causes significant economic losses to the dairy industry. This study aimed to identify the trend of culling reasons and lifespan and estimate their genetic parameters. The cow history records and pedigree files of 11 large commercial dairy farms with cows culled from 1995 to 2015 were used. It is estimated that 18.6% of cows are culled voluntarily by farmers, while 81.4% of cows leave the herd involuntarily. Three main reasons for involuntarily culling were reproductive problems (25.9%), death and others (16.7%), and infectious diseases (14.3%). Over time, the distributions of culling reasons have altered with a reduction in "death and others", suggesting a better or more precise diagnosis of culling reasons and improvement in dairy farm recording systems. The average lifespan of cattle was 4.42 years with heritability of 0.14. The heritabilities of culling reasons were very low and ranged from 0.03±0.02 (metabolic and digestive disorders) to 0.08±0.03 (mastitis and udder problems). The significance of the maternal effect for some traits like mastitis indicates that it may be possible to improve an individual's health and, therefore, farm profitability genetically.