There are 1.5 billion cows on the planet. They are known producers of methane, but the gas is more likely to be burped out than released from the… other end
Cows have an intricate digestive system and their food makes a complex journey through a four-chambered stomach. A single mouthful of grass can be chewed for up to eight hours, and a cow makes 40,000 jaw movements a day chewing either fresh grass or regurgitated cud. The grass is transferred between the mouth and the stomach all day long, and with this constant regurgitation comes constant burping.
Their stomachs contain over 400 species of bacteria that help break down the food in the gut. These microbes produce methane as a by-product, which builds up in the empty stomach space and is eventually released through the mouth. Domestic cattle emit almost 20 per-cent more gas than global transport.
This is only a problem with domestic cows as they have been bred to produce more milk than their wild ancestors. Wild cows are seasonal breeders, so only produce milk when they have newborns once a year. The increased appetite of farmed cows is what makes them produce so much harmful gas.
Image from flickr.com/photos/pepemczolz