The major culprits are the nitrous oxide that comes from the manure created by large livestock operations, and the methane emitted in cow burps and farts. (discovermagazine.com)
Methane, for example, is about 11 percent of greenhouse gas emissions — and no, not from cow farts — actually cow burps. (newhope.com)
In addition, cows burp lots of methane, and their manure also releases this potent greenhouse gas. (sciencedaily.com)