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

This study estimated the genetic parameters of productive and reproductive traits of Iranian Holstein cattle from data recorded between 2006 and 2018. The data analysis was performed using animal model, including the record of the first parity and the first three lactation records. Heritability values for milk, fat, and protein 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 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. Repeatability for milk, fat, and protein yield was 0.38 ± 0.002, 0.34 ± 0.002, and 0.36 ± 0.002, respectively. Positive genetic trend was observed 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 of the farms including feed quality and disease control have been improved. The average heritability for milk, fat, and protein yield 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 demonstrates the improvement of breeding values in Iranian Holstein cattle.