Abstract: [Objective]This study provided data support for the promotion and application of linear evaluation of body size defect traits of dairy cows,in order to improve the genetic improvement effect of large-scale dairy farms and improve the production level of pasture. [Method]Based on the linear evaluation results of body size of dairy cows from three large-scale pastures in southern Xinjiang in 2019 and 2022,combined with the determination results of DHI,linear evaluation analysis of body size defect traits of dairy cows was conducted. [Result]According to the results of linear genetic assessment of defects in 2019,after targeted improvement through genetic improvement,the proportion of main defect traits in the three pastures in 2022 decreased significantly,and the average daily yield per unit area increased by 5.8 kg compared with that in 2019（P<0.01）.Compared with 2020,the average somatic cell count decreased by 237 000 per mL（P<0.01）,the average milk fat percentage and milk protein had no significant difference （P> 0.05）,but milk protein was significantly improved. [Conclusion]The application of linear evaluation method for the size defect of dairy cows has important guiding significance for the genetic improvement of large-scale dairy farms,which can effectively improve the production performance of pasture cows and rapidly improve the population genetic level.

Key words: linear evaluation of body size, defect traits, genetic improvement, production performance of dairy cows