[Objective]The aim of the experiment was to study the effects of adding isoacids to periparturient diets on rumen microbiota,milk yield,milk fat rate and milk protein rate of dairy cows,and to provide a theoretical basis for the rational use of isoacids additives in dairy cows production.[Method]18 periparturient Chinese Holstein cows with the 3rd lactation and similar production dates were randomly divided into 3 groups(6 replicates per group,1 cow per replicate),the cows in control group(group C)were fed a basal ration,and in experimental groups were added 30(group A)and 60 mL/d of isoacids(group B),respectively,to the basal diet.The period of pre-feeding was 10 d,and the main test started from 21 d pre-partum to 21 d postpartum.Milk samples were collected from all cows at 10 and 21 d postpartum for determination of milk composition.Rumen fluid was collected from all cows using a rumen catheter before morning feeding at 21 d postpartum for determination of rumen fermentation parameters and microbial diversity.[Result]①Milk yield,milk fat rate and milk protein rate of cows in groups A and B were significantly higher than those in group C(P＜0.05).② Acetic acid and total volatile fatty acids(TVFA)were significantly higher in group B than that in group C(P＜0.05).③ The main dominant groups at the level of rumen microbiota of cows in the three groups were Bacteroidota and Firmicutes,and the relative abundance of Bacteroidota was significantly higher in group B than that in groups A and C(P＜0.05),whereas the relative abundance of Firmicutes was significantly lower than that in groups A and C(P＜0.05).The main dominant rumen microbial genera in three groups were Prevotella,Rikenellaceae_RC9_gut_group,Butyrivibrio and F082 unclassified taxa.The relative abundance of Butyrivibrio was significantly lower in groups A and B than that in group C(P＜0.05).④ Milk yield,milk fat rate and milk protein rate were significantly positively correlated with Bacteroidota and Prevotella(R＞0.5,P＜0.05),and significantly negatively correlated with Firmicutes,Spirochaetota and Butyrivibrio(R＜-0.5,P＜0.05).[Conclusion]Adding isoacids to the ration of periparturient dairy cows could increase the VFA content in rumen and increase milk yield,milk fat rate and milk protein rate,in which the addition of 60 mL/d of isotonic acid was more advantageous for improving the rumen development and production performance of dairy cows.
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