Effect of postextraction algal residue supplementation on the ruminal microbiome of steers consuming low-quality forage

Cattle consuming low-quality forages (LQF) require protein supplementation to increase forage utilization via ruminal fermentation. Biofuel production from algal biomass results in large quantities of postextraction algal residue (PEAR), which has the potential to elicit LQF utilization responses similar to cottonseed meal (CSM); however, its effect on ruminal bacterial communities is unknown. Five ruminally and duodenally cannulated Angus steers in a 5 × 5 Latin square had ad libitum access to oat straw diets. Treatments were infused ruminally and consisted of an unsupplemented control; PEAR at 50, 100, and 150 mg N/kg BW; and CSM at 100 mg N/kg BW. Ruminal samples were collected 4 h after supplementation on d 14 of each period and separated into solid and liquid fractions. Each sample was extracted for genomic DNA, PCR amplified for the V4 to V6 region of the 16S rRNA, sequenced on the 454 Roche pyrosequencing platform, and analyzed using the QIIME pipeline. Weighted UniFrac analysis and Morisita-Horn index demonstrated different community composition between liquid and solid fractions. Measures of richness including observed operational taxonomic units (OTU) and abundance coverage estimator metric decreased with greater PEAR provision (P ≤ 0.09). There were 42 core microbiome OTU observed in all solid fraction samples while the liquid fraction samples contained 30 core OTU. Bacteroidetes was the predominant phylum followed by Firmicutes in both fractions, which together characterized more than 90% of sequences. Relative abundance of Firmicutes increased with PEAR supplementation in the liquid fraction (linear, P = 0.02). Among Firmicutes, Lachnospiraceae, Ruminococcaceae, and Clostridiaceae families increased in the liquid fraction with greater PEAR supplementation (linear, P ≤ 0.03). Prevotella represented over 25% of sequences in all treatments, and relative abundance decreased in the solid fraction with increasing PEAR provision (linear, P = 0.01). Fibrobacter and Treponema decreased in the liquid fraction with increasing PEAR (linear, P < 0.10). Results suggest PEAR supplementation increased forage utilization by increasing members of Firmicutes within the liquid fraction of the rumen microbiome.