Abstract: 【Objective】 To fulfill the need of seasonal management modification of lactating cows. 【Method】 the effect of natural month, parity, and their interaction on milk components were analyzed in the present study. Data were collected from a DHI database of lactating Chinese Holstein cows in the north part of china. Original data were screened and group according to parity (1-4). A total of 6114 milk protein content records and 5871 milk fat content records were analyzed by GLM procedure of SAS. 【Result】The Duncan multiple comparison of natural months, regardless of parity (only parity 1 to 4), demonstrated that the milk compositions of different months showed significant difference (P＜0.05), although the data between some different months showed no significant difference. The milk protein percentage in September reached the highest (3.187%), and in July the lowest (3.016%). Milk fat percentage in February was the highest (4.137%), and in July the lowest (3.845%).The same multiple comparison of different parity, also regardless of different months (1-12 months), demonstrated that the milk composition data of different parities showed significant difference (P＜0.05), although the data between some parities showed no significant difference. The milk protein percentage reached the highest in parity 2 (3.114%), and the lowest in parity 4 (3.066%). The milk fat percentage reached highest in parity 2 (3.983%) and parity 3 (3.973%), respectively; and the lowest in parity 4 (3.923%). In addition, the relation equation between the milk protein percentage (MPP, %) or the milk fat percentage (MFP, %) of different parities and the natural months in mixed cow herd was built using Model Wood, i.e. MPP=3.094x-0.0464×e0.0117x, MFP=4.2116x-0.0344×e0.0276x, x as month. 【Conclusion】The natural months, milking parities and their interaction had significant affects on milk composition including milk protein percentage and milk fat percentage, and milk composition had wood pattern changing relationship with natural months respectively.

Key words: Holstein cows , milk compositions , natural months , lactation parity , model