Abstract:

Abstract: To improve the accuracy of breeding , the effects of calving monthes and lactations must be considered. This study is based on the milk yield records of 815 Chinese Holstein Dairy cattle from HeBei ShuangWa dairy farm . The adjusting coefficients of milk yield with calving monthes and lactations were investigated with the simple statistical polynomial regression analysis methord and the least Square method . Besides,a comparision study on the two different methods was carried out. Results shows that there was no significant difference between the milk yield estimited by the adjusting coefficients and the actual calculated 305d milk yield value. But there was a significant difference between the two methods on milk yield estimited at parity Ⅰ(（P=0.04<0.05）,and milk yield estimited by the adjusting coefficients of the least square method were much closer to the actual values in all the parities fromⅠto Ⅳ .