Short answers, pulled from the story.
Enteric fermentation is a digestive process in which microorganisms break down carbohydrates inside an animal's gut. In ruminants, over 200 species of microorganisms carry out fermentation inside the rumen, producing methane as a byproduct; most of it is belched out by the animal.
The Food and Agriculture Organization estimated that ruminant livestock contribute around 34.5 percent of total anthropogenic methane emissions. In the United States in 2007, enteric fermentation produced 139 teragrams of CO2 equivalents, equal to 2.3 percent of the country's net greenhouse gas output that year.
Kangaroos classified as Macropodids produce 80 percent less methane than cows because their digestive systems are dominated by bacteria of the family Succinivibrionaceae. These bacteria produce succinate rather than methane when breaking down lignocellulose, using alternative proton acceptors that bypass methane-forming pathways.
Researchers are exploring microbial engineering to alter the rumen microbiota of high-methane livestock to resemble the Macropodidae microbiota. Diet additives such as Asparagopsis taxiformis (red seaweed) and the compound 3-nitroxypropanol (3-NOP), which blocks the final step of methane synthesis in the rumen, have also shown significant reductions in feedlot cattle.
Methane production represents an energy loss to the animal ranging from 2 to 12 percent of gross energy intake. Reducing that loss without affecting animal production would improve feed conversion efficiency alongside cutting greenhouse gas emissions.
Feedlot emissions represent only around 11 percent of overall cattle emissions, meaning that interventions applied through feedlot feed additives, while measurable, leave the majority of cattle-related enteric methane unaddressed.