Short answers, pulled from the story.
Enteric fermentation is a digestive process in ruminant animals where microbes break down cellulose inside the rumen. Methane gas forms as a byproduct during this chemical reaction when carbohydrates are converted into simple molecules.
The Food and Agriculture Organization estimates that ruminant livestock contribute around 34.5 percent of total anthropogenic methane emissions. This figure represents a significant portion of greenhouse gases produced globally from agricultural sources.
Kangaroos produce 80 percent less methane because their gut microbiota belongs to the family Succinivibrionaceae which produces succinate instead of methane. This metabolic route allows them to utilize other proton acceptors rather than forming large amounts of end-product methane.
Enteric fermentation ranked as the second largest source of methane emissions in the United States between 2000 and 2009. In 2007 these emissions accounted for 2.3 percent of net greenhouse gases produced nationwide with 139 teragrams of carbon dioxide equivalents released.
Asparagopsis taxiformis red seaweed reduces methane emissions when fed to cattle in feedlots. Another compound called 3-nitroxypropanol inhibits the final step of methane synthesis inside the rumen.