Abstract: 【Objective】 The purpose of the experiment was to explore the changes of bacterial composition,abundance and diversity in the feces of pure blood ponies in the middle and later stages of lactation,so as to provide reference basis for optimizing nursing and efficient and healthy breeding of foals during lactation.【Method】 Five male foals with similar birth date and weight of (144.33 ±16.10) kg in the middle and later stage of lactation were selected for 60 days feeding experiment.Fecal samples were collected without DNA enzyme tube before weaning (3,4 and 5 months old),and the microbial diversity in fecal samples was detected by IlluminaMiSeq high-throughput sequencing platform.【Result】 ①There were 627 OTU in fecal flora of 3-,4-and 5-month-old foals,and the number of endemic OTU was 202,177 and 194,respectively,but there was no significant difference in Chao1,ACE,Shannon and Simpson index among the three stages (P>0.05).The results of principal component analysis showed that the difference of microflora in the feces was small and stable.②The dominant phylums in the faeces of 3-,4-and 5-month-old foals were Firmicutes,Bacteroidota,Actinobacteriota,Verrucomicrobiota and Patescibacteria,while the dominant families were Lachnospiraceae,Planococcaceae,Micrococcaceae,Oscillospiraceae and Anaerovoracaceae.The dominant genus were Arthrobacter,Psychrobacillus,unclassified_Lachnospiraceae,uncultured_rumen_bacterium and Christensenellaceae_R_7_group.③At the phylum level,the relative abundance of verruca in the feces of 5-month-old foal was significantly lower than that of 3-month-old,the relative abundance of Spirochete was significantly higher than that of 3- and 4-month-old,and the relative abundance of Fibrillaria was significantly higher than that of 4-month-old (P＜0.05).At the family level,the relative abundance of Ackermanniaceae in the feces of 3-month-old foal was significantly higher than that of 4- and 5-month-old (P＜0.05).At the genus level,there was no significant difference among the ten dominant bacteria of each month (P＞0.05).【Conclusion】 To sum up,in the same feeding environment,the diversity index of fecal microflora of foal fluctuated with the increase of age,and the dominant species of the top 10 microorganisms in feces were the same,but the relative abundance was different.and the differential bacteria in foal feces decreased with the increase of age.

Key words: thoroughbred horse; foal; fecal flora; diversity analysis