The digestive tracts of ruminant (cud-chewing) animals such as cattle, sheep, and goats convert lignocellulosic plant matter to short-chain fatty acids used for nourishment with unparalleled efficiency, thanks to the activity of symbiotic microbes in the rumen. Rumen microbes play a vital role in allowing ruminant livestock to break down the food they eat, and produce milk, meat and wool which help support the livelihoods and food security of over a billion people worldwide. The process, however, is also the single largest human-influenced source of the greenhouse gas methane (CH4), with these animals releasing approximately 138 million U.S. short tons of CH4 into the atmosphere each year.