PSIV-5 Characterization of the Fecal Bacterial Communities of Grass-fed and Grain-fed Bison Heifers

In comparison to the rumen, the bacterial communities of the hindgut have remained largely unexplored in ruminants. They not only strongly influence host health, but also efficiency, notably by continuing fermentation of feed that escaped foregut digestion. In non-domesticated ruminants, such as the North American bison, they are thought to contribute to the higher efficiency of their host on feed of poor quality. To gain further insight on this gut microbial ecosystem, fecal bacterial community composition of bison heifers raised at two locations [Standing Butte (n=17), SD, and Blue Creek (n=17), NE] were investigated. Each animal was sampled once while on pasture, then after 100 days on a grain-based diet. Data generated from Illumina MiSeq (2×300) sequencing of PCR amplicons targeting the V1-V3 region of the 16S rRNA gene were analyzed using a combination of custom Perl scripts, and publicly available software (Mothur v.1.40, RDP classifier and NCBI Blast). A total of 26,379 and 13,294 species-level operational taxonomic units (OTUs) were identified from Standing Butte and Blue Creek samples, respectively, with 446 and 281 OTUs shared between diets at each respective location. Further analysis of the most highly represented OTUs from each ranch revealed that the abundance of six OTUs differed between diets in Standing Butte heifers compared to nine OTUs in Blue Creek heifers (Kruskal-Wallis sum-rank test; P < 0.05). These included OTUs SD_Bb-00727 (µgrass = < 0.01% vs µgrain = 13.13%) and SD_Bb-00728 (µgrass = 5.62% vs µgrain = < 0.01%) from the Standing Butte samples, as well as OTUs SD_Bb-00730 (µgrass = 0.01% vs µgrain = 10.21%) and SD_Bb-00745 (µgrass = < 0.01% vs µgrain = 3.5%) from the Blue Creek samples. Together, these results indicate that the composition of hindgut bacterial communities of the North American bison are greatly affected by changes in diet.