Abstract: 【Objective】 The purpose of this experiment was to study the effects of supplementary feeding of Chinese herbal medicine and active dry yeast preparation on diarrhea rate and intestinal flora diversity of lactating calves,and to provide theoretical basis for exploring the mechanism of action on intestinal health of lactating calves.【Method】 Twenty-four lactating calves of Yanbian Yellow cattle with similar body weight,month age and good body condition were randomly divided into three groups,with 8 calves in each group (5 males and 3 females).The calves in control group (group Ⅰ) were fed with basal diet,while in the Chinese herbal medicine group (group Ⅱ) were supplemented with 0.5% Chinese herbal medicine preparation in the basal diet,and the yeast group (group Ⅲ) was supplemented with 1 g/d Raman active dry yeast in the basal diet.The feeding experiment lasted for 31 days，the pre-test period was 10 days and the formal test period was 21 days.Before the morning feeding on the end of the feeding trial,the fresh fecal samples from the rectum of calves in the pasture were collected aseptically with cotton swabs and stored in a refrigerator at ―80 ℃ for testing.The feces collected from the rectum of calves were sequenced to compare the differences in bacterial diversity between groups Ⅱ,Ⅲ and group Ⅰ.【Result】 ①Compared with group Ⅰ,ADG of calves in groups Ⅱ and Ⅲ was significantly increased (P＜0.05),F/G,diarrhea rate and fecal score of calves were significantly decreased (P＜0.05).②In terms of rumen flora diversity,compared with group Ⅰ,there was no significant difference in Alpha diversity indexes (ACE,Chao1,Coverage,Shannon and Simpson)in the two treatment groups (P＞0.05).③In terms of rumen flora distribution,at phylum level,the dominant phylum in both treatment groups were Firmicutes and Bacteroidetes.At genus level,the dominant genus in the two treatment groups were Ruminococcaceae_UCG-005,Rikenellaceae_RC9_gut_group and [Eubacterium]_coprostanoligenes_group.Compared with group Ⅰ,the relative abundance of Rikenellaceae_RC9_gut_ group in groups Ⅱ and Ⅲ was significantly increased (P＜0.05),while there was no significant difference in the relative abundance of other microbiota at phylum and genus levels (P＞0.05).【Conclusion】 Supplementation of 0.5% Chinese herbal medicine feed additive or 1 g/d active dry yeast preparation could reduce the diarrhea symptoms of lactating calves to varying degrees,improve the diversity of intestinal flora,and promote the healthy development of the intestine.

Key words: lactating calves; Chinese herbal medicine; active dry yeast; diarrhea rate; bacterial diversity