Determining which animal passes gas the most remains scientifically unproven, though researchers point to hindgut-fermenting herbivores as prime candidates. While livestock produce massive amounts of methane primarily through burping rather than flatulence, exact individual rankings are hindered by the immense difficulty of measuring intestinal gas across the animal kingdom.
Flatology, the study of flatulence, serves as a serious discipline helping biologists understand animal diets and digestion. Creatures ranging from whales to snakes and sloths pass gas, but calculating precise volumes per species presents a formidable challenge, Live Science reported.
Measuring Methane Across Species
“Getting quantitative measurements for farts per animal is pretty difficult,” Nick Caruso, a data scientist and co-author of Does It Fart?: The Definitive Field Guide to Animal Flatulence, told Live Science in an email.
Researchers measure animal methane production by placing subjects inside respiration chambers or inserting stomach capsules that release tracer gases. Alternatively, scientists capture breath samples at feeding and milking stations to track emissions.
Livestock represent major methane emitters, with a recent report placing their total emissions at 117 teragrams per year. Ermias Kebreab, a professor of animal science at the University of California, Davis, explained to Live Science in an email that the vast majority of agricultural livestock methane is actually released via burping rather than flatulence.
Where Gut Fermentation Dictates Gas Release
Herbivores rely on gut microbes to break down plant material through fermentation, releasing gases like methane and carbon dioxide. The specific location of this fermentation within the digestive tract dictates how the gas ultimately exits the animal’s body.
Animals fermenting food near the front of the digestive tract mostly belch out the resulting gas.
“Some of this gas is absorbed into the bloodstream and exhaled, the rest tends to leave by the nearest exit — animals that ferment their food toward the front of the digestive tract mostly burp it out, while those that ferment it toward the back mostly pass it as wind,” Dr. Marcus Clauss, head of research and co-director of the Clinic for Zoo Animals, Exotic Pets and Wildlife at the University of Zurich, told Live Science in an email.
Cows, sheep, goats, and camels ferment food in a rumen located near the front of their digestive system. Matthew Hayek, an associate professor of environmental studies at New York University, noted in an email to Live Science that ruminants consequently discharge the majority of their methane through belching.
| Animal Group | Digestion Type | Primary Gas Exit Method | Annual Emissions / Impact |
|---|---|---|---|
| Ruminants (Cows, Sheep) | Foregut fermenters | Belching | 117 teragrams per year total livestock |
| Horses | Hindgut fermenters | Flatulence | 40 pounds (18 kg) per horse yearly |
| Termites | Hindgut fermenters | Flatulence | 10 teragrams per year globally |
Evaluating Hindgut Fermenters and Termites
Because meat eaters produce far less methane, herbivores stand out as the top contenders for high flatulence. Hindgut fermenters digest plant matter in the large intestine, making them prime suspects for passing wind.
Termites break down wood and grass in their hindguts with an estimated global population of 27 quadrillion individuals. Together, they emit 10 teragrams of methane annually, though soil bacteria consume a large proportion of these emissions.
Per individual animal, horses hold a leading measured title. A 2019 Intergovernmental Panel on Climate Change report notes horses emit around 40 pounds of methane each year.
Clauss remains skeptical of definitive rankings based solely on current metrics. “The ranking of horse as highest is only because it has been measured, but there are so many hindgut fermenters not measured, like rhino… Who knows?” Clauss told Live Science in an email.
When evaluated by body weight, semiaquatic rodents like the nutria generate higher methane emissions than horses.
According to Stefan Arndt, a professor of physiological and ecosystem ecology at the University of Melbourne in Australia, who shared this insight with Live Science via email:
