Effect of Post-extraction Algal Residue Supplementation on the Therumen Microbiome of Steers Consuming Low-quality Forage

The rumen microbiome is a dynamic environment consisting of bacteria, protist, and fungi responsible for fiber degradation. Advances in molecular techniques have enabled description of bacterial microbiome via pyrosequencing. Cattle consuming low-quality forage are often supplemented with protein to increase forage intake and digestion, but effect on the rumen bacterial community is unknown. Thus, increasing post-extraction algal residue (PEAR) and cottonseed meal (CSM) supplementation was provided to steers consuming oat straw to observe the rumen microbiome within the liquid and solid fraction. Weighted UniFrac analysis indicated different fraction-associated communities with greater similarity across treatments in the solid fraction. Bacteroidetes was the predominant phyla detected in all samples (>65%). Within Bacteroidetes, Prevotella was the most abundant genus. In the liquid fraction, Lachnospiraceae, Ruminococcaceae, and Clostridiaceae increased with PEAR provision (P < 0.05). Similar proportions of bacteria between unsupplemented control and CSM supplemented steers indicate factors other than N supply may impact ruminal bacteria populations. A second experiment evaluated the effect of supplemental CSM or dried distillers? grain (DDG) for Brahman steers consuming rice straw. Total digestible OM intake and total tract OM digestion increased linearly with additional CSM and DDG provision (P < 0.01). Provision of CSM increased ruminal ammonia linearly (P < 0.01), but DDG supplementation resulted in a quadratic response (P = 0.02). Overall, protein supplementation may increase LQF utilization via changes in the rumen microbiome.