The aim of this study was to investigate the effects of adding different levels of yeast β-glucan on performance,rumen fermentation parameters and microflora structure of dairy cows in middle lactation period.Selecting 30 healthy dairy cows[similar parity was(2.74±0.71),milk production was(40.32±5.66)kg/d,and days in milk was(95.15±46.25)d]in middle lactation period were randomly divided into 3 groups with 10 heads in each group.Dairy cows in the control group(C group)were fed total mixed diet(TMR),and those in the experimental groups(L and H groups)were supplemented with 20 and 40 g/(d·head)yeast β-glucan,respectively.At days 1,15,30,45 and 60 of the formal trial period,milk and rumen fluid samples were collected to determine the performance,rumen fermentation parameters and rumen microflora structure.The results showed as follows:1)milk yield of cows in L group was significantly higher than that in C group(P＜0.01),and milk fat percentage,4％milk fat corrected milk yield and lactose percentage in L and H groups were significantly higher than those in C group(P＜0.05).2)Compared with C group,the contents of acetic acid and butyric acid in rumen in L group were significantly increased(P＜0.05),but the contents of propionic acid,ammonia nitrogen and acetic acid/propionic acid were not significantly different(P＞0.05).3)Based on 16S rRNA high-throughput sequencing technology,it was determined that Firmicutes and Bacteroid-ota were the dominant bacteria in the rumen of dairy cows in the 3 groups at the phylum level.At the generic level,Prevotella was the dominant bacteria.A total of 56 distinct species were detected in rumen fluid of dairy cows by LEfSe analysis(linear discriminant analysis≥ 2,P＜0.05),of which 24 species played an important role in C group and 32 species played an important role in L group.In conclusion,dietary supplementation of yeast β-glucan can significantly improve milk yield and milk quality of dairy cows during middle lactation peri-od,and also have certain effects on rumen fermentation process and microflora structure.[Chinese Journal of Animal Nutrition,2023,35(12):7865-7878]
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