The Environmental Protection Agency says landfills were responsible for 17% of U.S. methane emissions in 2018, behind oil and gas emissions (28%) and agriculture (40%). Cattle and other ruminant mammals contribute both through the gas that is a byproduct of their digestive systems and related "manure management," the EPA says.
Over a 100-year period, methane packs 25 times the relative impact of carbon dioxide, making it an important greenhouse gas to monitor for its impact on climate. Globally, cattle are responsible for 75% of animal methane emissions, with other ruminants such as sheep and goals also a factor.