RUMINANT NUTRITION SYMPOSIUM: How to use data on the rumen microbiome to improve our understanding of ruminant nutrition.

Metagenomics and high-throughput sequencing have greatly expanded our knowledge of the rumen microbiome. Surveys of all 4 cellular microbial groups (bacteria, archaea, protozoa, and fungi) reveal profound diversity. Even so, evidence exists for core members to perform key degradative or fermentative roles for the host. Some core members are functionally similar yet taxonomically diverse, and noncore members are particularly diverse and probably vary among diets, animals, and over time after feeding. Gains in functional knowledge are being made and offer much potential not only to improve fiber digestibility, decrease methane emissions, and improve efficiency of nitrogen usage but also to help explain the differences in nutrient digestibility or feed efficiency among animals fed the same diet. Integrated research using metagenomics, bioinformatics, traditional ruminant nutrition, and statistical inferences have provided opportunities for ruminant nutritionists and rumen microbiologists to work synergistically to improve nutrient utilization efficiency while minimizing output of wastes and emissions of methane and ammonia. Examples we highlight include residual feed intake, rumen biohydrogenation of unsaturated fatty acids, and dietary inclusion of ionophores. However, there are still some quantitative limitations in approaches being used. This review addresses knowledge gained and current limitations and challenges that remain.