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.

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

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.

229 Characterization of the rumen bacterial communities of bison heifers maintained on a pasture-based diet

The North American bison has evolved to thrive on a diverse range of habitats and climate. As a ruminant, it is dependent on the metabolic activities of symbiotic microorganisms to digest the plant fibers that make up the majority of its diet. To gain further insight into the bison rumen environment, which has remained largely unexplored, the primary objective of this study was to determine the diversity and composition of ruminal bacteria in bison fed a pasture-based diet. Ruminal content from 19 heifers maintained on pasture at the Standing Butte Ranch (North Stanley, South Dakota, USA) was collected by stomach tubing. Following extraction of microbial genomic DNA, PCR was performed to amplify the V1–V3 region of the 16S rRNA gene, then amplicons were sequenced using an Illumina MiSeq(2×300) platform. Next-generation sequence data was then analyzed using a combination of custom Perl scripts, publicly available software (Mothur v. 1.40) and online tools (RDP classifier and NCBI Blast). Bacteroidetes and Firmicutes were found to be the dominant phyla in the rumen environments analyzed, together representing 85.3% to 96.6% of sequence reads in individual samples. In contrast, the ratio of Bacteroidetes to Firmicutes showed a much broader range (0.57 to 3.90), suggesting that the rumen bacterial communities of the sampled animals exhibited a wide array of distinct composition patterns. However, Pearson correlation analysis did not support an association between the Shannon alpha diversity index and the abundance of either Bacteroidetes or Firmicutes (P > 0.05). Interestingly, Pearson correlation analysis supported a positive association between Bacteroidetes and Fibrobacteres (P < 0.05), as well as between Firmicutes and Planctomycetes (P < 0.05). Together, these results suggest that at least two rumen enterotypes, Bacteroidetes-Fibrobacteres and Firmicutes-Planctomycetes, can be distinguished in the rumen of North American bison heifers maintained on a pasture-based diet.