Abstract:This paper explored the nutritional components and microbial indicators of fresh milk from largescale pastures in four different regions， namely Shanxi， Shaanxi， Inner Mongolia， and Gansu， assessed the factors causing the quality differences of fresh milk， and determined the content of β-casein in fresh milk to investigate the effects of season， lactation period， and genotype of dairy cows on its content. The research found that the nutritional indicators of fresh milk in different regions varied significantly and were greatly influenced by the season. The nutritional quality of fresh milk in the fourth quarter was relatively high， with a protein content of 3.46 g/100 g and a fat content of 3.85 g/100 g. However， the somatic cell count and psychrophilic bacteria indicators were the highest. These indicators were mainly influenced by climatic conditions and the management level of the pasture. In addition， the content of A2 β-casein in fresh milk was significantly influenced by the genotype of dairy cows， and the lactation period and season also had certain effects on its content. Principal component analysis and hierarchical cluster analysis indicated that the fresh milk from the four regions could all be well distinguished and clustered into two categories.