0812 Investigation of equine hindgut microbiota development in young horses

The gastrointestinal microbiota is an important contributor to the health and nutrition of mammals. Since the gut of young mammals is devoid of microorganisms at birth, its colonization by symbiotic microbes and their arrangement into complex communities is a critical aspect of a young host's post-natal development. Compared to most other experimental animal models or livestock, the gut microbiome of the horse remains largely unexplored, particularly in young foals. To gain further insight on development of the equine hindgut bacterial microbiota, fresh fecal samples were collected from 2 foals over their first 4 mo of life. Fecal samples from their respective dams were also collected as representative of mature hindgut microbial communities. Microbial DNA was extracted from the samples and used as template to generate PCR amplicons of the bacterial 16S rRNA gene (V1-V3 region), which were sequenced using the Illumina MiSeq 2×300 platform. A combined total of 333,300 high quality sequence reads corresponding to the expected full length PCR amplicons were used to determine the hindgut bacterial composition of the sampled animals. The number of sequence reads per sample ranged between 17,613 and 59,964. At the youngest age sampled (3.7 wks), the bacterial profile consisted predominantly of Verrucomicrobia (50.9%) and Bacteroidetes (22.9%) related sequences, with the most abundant species-level OTU (operational taxonomic unit) for each phylum found at 44.9% (OTU SDEc-1) and 10.7% (OTU SDEc-2), respectively. At later time points (5.86–18.57 wks), Verrucomicrobia representation was reduced dramatically (0.7– 2.1%), while Bacteroidetes appeared to be maintained within a similar range (20.3– 37.7%). However, population shifts were detected within Bacteroidetes. For instance, OTU SDEc-2 abundance was greatly reduced during this period (< 0.05%), and OTU SDEc-3 was transitionally higher (range of 5.1–7.2%) between 5.6 wks to 9.57 wks. We also observed an overall increase from 13.1% to 65.0% in Firmicutes representation among foal samples during the sample period. In comparison with the fecal bacterial composition of their dams (2.2–15.5% Bacteroidetes; 71.6–83.3% Firmicutes), our results suggest that hindgut bacterial populations in horses younger than 4 mo have not yet developed a mature microbiota.