206 Characterization of the Rumen Bacterial Communities of Grass-fed and Grain-fed Bison Heifers

Abstract

Abstract The ruminal bacterial environment of the North American bison has remained largely unexplored. The current study aimed to compare the diversity and composition of ruminal bacteria between bison heifers on two different diets. Stomach tubing was used to collect rumen fluid from lifetime grass-fed heifers between 27 and 30 months of age distributed between 2 ranches located in Standing-Butte (n = 17), SD, and Blue-Creek (n = 17), NE, respectively. A second set of samples was collected after the same individuals had been transitioned to a grain-based diet for 100 days. Bacterial composition was determined by Illumina MiSeq (2×300) sequencing of PCR amplicons generated from the V1-V3 region of the 16S rRNA gene. Next-Generation Sequence data was analyzed using a combination of custom Perl scripts, and publicly available software (Mothur v.1.40, RDP classifier and NCBI Blast). Taxonomic analysis identified Bacteroidetes and Firmicutes as the dominant phyla across all samples analyzed. A total of 61,746 and 68,437 species-level Operational Taxonomic Units (OTUs) were identified in grass-fed heifers, in contrast to 15,003 and 23,458 OTUs that were found in the same animals on a grain-based diet. A comparative analysis using the most abundant OTUs from each group was conducted using the Kruskal-Wallis sum-rank test. In the Standing Butte heifers, 24 abundant OTUs were found to be different between diets (P < 0.05), including BP_31-10446 (µ grass = 0.3% vs µ grain = 3.2%) and BP_25-00404 (µ grass = 0.4% vs µ grain = 4.1%). In the Blue Creek heifers, 20 of the most abundant OTUs were found to be different between diets (P < 0.05), including BP_18-00869 (µ grass = 1.4% vs µ grain = 0.4%) and BCRC_1-00422 (µ grass = 0.07% vs µ grain = 4.4%). Together, these results indicate that the rumen of the North American bison harbors highly diverse bacterial communities that undergo dramatic changes in response to changes in diet.