Intake of low-quality forage (LQF) in the absence of protein supplementation fails to meet ruminal microbial nitrogen requirements, decreasing forage utilization and animal performance. Supplementation of both protein and starch is used to ameliorate the negative effects of LQF; however, the effect of supplementation on ruminal microbial communities is not well-understood. This experiment evaluated the effect of protein (130 mg N/kg BW) and starch supplementation (2 or 56% starch) on ruminal microbial gene expression in cattle consuming LQF (3.5% CP). Time of sampling, rather than concentration of starch, had a greater effect on microbial expression. At four hours post-supplementation, upregulated methanogenesis pathways were primarily expressed by Thermoplasmatales and downregulated methanogenesis pathways were principally expressed by Methanobrevibacter. Increased starch supplementation resulted in the differential regulation of methanogenesis pathways with upregulated genes mainly expressed by Thermoplasmatales and downregulated genes mostly expressed by Methanomethylophilus alvus. Sampling time affected the number of differentially expressed bacterial carbohydrate active enzymes, but concentration of starch supplementation did not. These results indicate that both time post-feeding and concentration of starch supplementation affect the microbial genes involved in methane and carbohydrate metabolism. Continued research in this area may help develop optimal supplementation strategies for beef cattle.

Read the full article in the Journal of Animal Science.