PSIV-14 Effects of DDGS and/or canola meal on rumen microbiome of growing steers.

Abstract The objectives of this study were to characterize rumen microbial composition in response to feeding dried distillers grains with solubles (DDGS) and/or canola meal in finishing diets. Six Jersey steers with rumen and duodenal cannulas were allocated in a duplicate 3 × 3 Latin square design. Treatments were as follows: 1) DDGS at 20.0% (DM basis) inclusion [CON], 2) 50% of DDGS replaced by Canola meal [CM50], 3) 100% of DDGS replaced by Canola Meal [CM100]. Each of the three periods in the Latin Square lasted 17-d, consisting of a 10-d diet adaptation followed by a 7-d collection period. Rumen evacuations were performed on d17 and subsamples of rumen fluid (50-ml) were stored at -80◦C until further processing. The DNA extraction was performed using a bead beating method. Sequencing was performed at the SDSU Seeds Laboratory (Brookings, SD) via full length 16S rRNA Gene using Oxford Nanopore long reads. All samples had >100,000 reads. The EMU Implementation was run through SILVA 16s Ver.132 at 97% similarity to classify long read amplification in CLC Genomic Workbench. A Wald test was performed to test for differential abundance in pair comparisons. To make all pair-wise comparisons between the three treatment groups, three contrasts were created as follows: CON vs. CM50, CM50 vs. CM100, and CON vs. CM100. We identified 1,776 unique operational taxonomic units (OTU) throughout all treatment groups. At the genus level, results showed that the most abundant group throughout all treatments was Prevotella, making up ~14% of quality-filtered reads per sample. We found 9 differentially abundant genera in CON vs CM50, 15 in CM50 vs CM100, and 10 in CON vs CM100. At the OTU level, uncultured species affiliated to Erysipelotrichaceae and Kandleria, respectively, were significantly greater (P < 0.001) for CM100 compared to CON. Known members of these taxonomic groups have been reported to ferment a wide range of sugars to produce lactate, which corroborates with our findings that lactate concentrations were greater for CM100 than CON. The abundance of an OTU assigned to Prevotellaceae was also affected by treatments, being greater (P < 0.001) for CON compared to CM100. As members of the Prevotellaceae family are characterized by their versatile metabolic capabilities, these differences may be the result of compounds present in canola meal that specifically affect particular species. The datasets obtained in this study thus revealed significant alterations in the composition of the rumen microbial communities in response to the inclusion of DDGS and canola meal in finishing diets. To complement this data, we are currently evaluating nutrient flow and digestibility to better understand the contribution of rumen microbes to nutrient metabolism in cattle.