Estimation of genetic parameters of the productive and reproductive traits in Iranian Holstein cattle using single and repeated records

Abstract This study estimated the genetic parameters of productive and reproductive traits of Iranian Holstein cattle from data recorded between 2006 to 2018. The data analysis was performed using an animal model, including the record of the first parity and the first three lactation records. Heritability values for milk, fat, and protein traits using a single record animal model were 0.29 ± 0.005, 0.22 ± 0.005, and 0.24 ± 0.005, respectively. The heritability of these traits based on a repeated records animal model was estimated to be 0.19 ± 0.001, 0.15 ± 0.005, and 0.17 ± 0.006, respectively. Furthermore, the heritability of age at first calving (AFC) and length of lactation (LL) traits were 0.16 ± 0.004 and 0.02 ± 0.002, respectively. Estimated repeatability for milk, fat, and protein production was 0.38 ± 0.002, 0.34 ± 0.002, and 0.36 ± 0.002, respectively. Positive genetic changes occurred over the years of the study for production traits. Evaluation of the effect of herd-year-season (HYS) on the productive traits revealed that the management and environmental conditions improved. The average estimate of heritability for milk, fat, and protein yields and AFC indicates the possibility of genetic improvement for these traits. Furthermore, the repeatability values show that the selection process can be performed based on the first lactation record. The positive genetic trend of productive traits validates the positive response to selection in Iranian Holstein cattle. Consequently, improving environmental and management conditions in Iranian dairy cattle herds is recommended, which will positively affect reproductive traits.