The Effect of Calving Season on Some of Productive and Reproductive Traits in Tehran Province's Holstein Cows

The aim of this research was to investigate the calving season effect on some of the productive traits including milk production, fat percentage and some of reproductive traits including pregnancy period and calf birth weight and also estimation of genetic parameters of studied traits too. In this study the data of 22360 Holestein dairy cows form Tehran province’s 65 herds of between 2012 to 2016 was used that were collected by the country animal breeding center. The study of fixed effects (HYS) and comparison of means was carried out with GLM Procedure of SAS 9.2 software. Estimation of genetic parameters was done by ASReml 3.0 software. The effect of calving season on all traits was significant (p